How To - Build a Cross-Band Full-Duplex AllStar Node Using a Mobile Radio
by David Gleason, NR9V

Introduction

AllStarLink Nodes can be built in many ways with various tradeoffs between cost, features, ease of construction, portability, audio quality and RF performance. Most nodes now available are small, simple nodes that support only half-duplex operation and often have low audio quality. Or another common design is to use old Motorola or similar radios, but these require special programming software and do not support cross-band full-duplex thus 2 radios and a duplexer would be required.

This guide shows how to build a node with a dual-band mobile radio that supports Cross-Band Full-Duplex operation while also being a full-featured radio that supports QSOs on analog FM repeaters, VFO and memory scanning, and simple front panel configuration. My other How-To Guide covers how to do this using 2 low-cost HTs, which is generally a more cost-effective way to go, but mobile radios can be a better option for base station use with an outdoor antenna or where maximum range is required.

AllScan ANF200 (w/Dell Wyse 3040, R1-ASL URI, and Kenwood TM-V71A)


Mobile Radios vs. HTs for use in a Full-Duplex AllStar Node

An ANF101 node with HTs can be built for well under $200, whereas an ANF200 mobile-radio node will typically be closer to $500, with the radio itself being $250+, an antenna and coax adding another ~$50+, and the MiniPC and USB Radio Interface (URI) adding another ~$100-150. A mobile-radio node with good outdoor antenna can have a range of ~50 miles depending on terrain and antenna height. HT-based nodes can also be used with an outdoor antenna by adding a ~$50 duplexer, in which case an HT-based node is still about half the price of a mobile-radio node but can give ~10-20 miles range. Thus mobile-radio nodes are more suited to applications that need 25+ Watts of output power, that can operate from an RV or parked vehicle, or where a modular, easy-to-build design is preferred.

Mobile-radio nodes are very easy to build if using a high-quality dual-band mobile such as a Kenwood TM-V71A or Yaesu FT-8800R. No mods are needed to the radio and no enclosure or other mounting hardware is needed. The mounting bracket that comes with most mobiles works great for attaching the MiniPC and URI, and the entire node can be assembled and wired in 1-2 hours. In contrast it can take 4-8 hours to make a full-duplex HT-based node that's properly optimized for RFI and noise. Mobile radios have less chance of RFI issues due to using an outdoor antenna that is typically at least 10-20 feet away from the node electronics. A higher-end mobile radio should also have better overall circuit design and power supply and I/O filtering than inexpensive HTs.

Mobile-radio nodes are typically used as Base-Station nodes at a home QTH, in an RV, or at a field day site for example, rather than actually "mobile". This is an important point to consider before going with a mobile, which are significantly more expensive and less power-efficient than HTs. Thus I only recommend going with a mobile-radio for a node radio if you need a lot of range (>~10 miles), already have a good outdoor antenna and 12V 15+Amp power supply/batteries, and if you would not generally take the node mobile or portable.

Table of Contents

Introduction
Overview
  History
  Node Components
Parts List and Component Options
  Main Components
  Mobile Radio
  USB Radio Interface
Setup Steps
  Debian & ASL Installation
  ASL Configuration
  Wiring Notes
  Radio Interface Wiring
Setup Steps (continued)
  Radio Settings
  Ferrite Filters
  Signal-To-Noise Ratio (SNR) Optimization
  Node Management
  WiFi Support, Portability
Full-Duplex Communication Benefits
FAQs
Node Notes / Instructions
Troubleshooting
Conclusion, Contact

Overview

Quick Demo Video of an ANF200 using a Yaesu FT-8800R and URI100


ANF200-8800R Back View showing Cables and Ferrite Filters


This uses a 5-16VDC Dell 3040 powered from the radio power cord with added PowerPole connectors.

Demo Video and Slideshow of an ANF200 using an Alinco DR-735T


History

AllStarLink (ASL) has been used for controlling repeater systems for 15+ years, supporting a high-precision multiplexing receiver system that precisely time-aligns audio feeds from any number of receivers, even with unpredictable delays that occur over various IP and wireless links. It's based on Asterisk, a powerful open-source PBX system that supports numerous features including full-duplex communications, conference calling, autopatch, integration with VOIP systems and equipment, voicemail, voice detection, support for a wide range of codecs, and extensive control and monitoring capabilities via web and IP interfaces, DTMF commands, scripting and macros.

An AllStar node is part of a comprehensive system of GigaBytes of software and millions of lines of code that make up Linux, Asterisk, ASL, Apache, PHP, SQLite, and 1,000's of other utilities and programs that come with Linux. Linux, Asterisk and ASL are 100% open-source and free, meaning that not only is it free but that anyone can look at the source code, see how it works, modify it or improve it.

Node Components

There are several main pieces to an AllStar node:

  1. A computing device. This can be a Raspberry Pi, any Intel/AMD PC or Mini/Thin-Client PC, or a "cloud" Linux server such as a linode.com VM. In the case of a cloud server an RTCM interface can be used which connects to a router and then to your radio (but which cost almost $300). RPis, the Dell Wyse 3040 and some other mini PCs use only about 5 Watts of power.
  2. A radio/audio/GPIO interface. This usually consists of a small PC Board with a C-Media CM108 or CM119 IC that interfaces to a USB port and provides an audio input, audio output(s), and GPIO lines for PTT, COS, and status LED(s). This is usually referred to as a URI (USB Radio Interface), or in the case of a radio-less node a UCI (USB Communications Interface).
  3. A node radio*. This is often built-in to Off-the-Shelf nodes as a small simplex radio module. However these modules may not have very good audio quality or RF specs. Real radios are definitely preferable, and are easier to configure and monitor through their front panel display, keyboard and LEDs.
  4. Last, some other radio is needed to then talk to the node with. It could be an HT, mobile rig or base rig. With cross-band full-duplex the node radio could for example Tx on ~431 MHz and Rx on ~147 MHz, and your other radio would Rx on ~431 and Tx on ~147.

*There are also radio-less nodes, which use just a speaker and mic, but don't give you the flexibility of being able to walk around your yard or neighborhood with an HT.

Smartphone/PC IAX apps such as DVSwitch Mobile (DVSM), iaxRpt and DroidStar can easily connect to a node. The DVSM 2.x Android app supports IAX client, Web-Transceiver, and Node modes. DVSM in Node Mode is a true AllStar node with its own ASL node number but with some major limitations. VOIP phones (such as any model supported by Hamshack Hotline) can be convenient and usually have a speakerphone feature, and SIP phone apps such as Linphone can also be used. Because VOIP phones don't have a PTT button however it is necessary to dial *99 to key up and then # to unkey, which is not nearly as convenient as a real radio or PTT mic. See this excellent article on how to set up VOIP phones/apps on AllStar nodes. This also covers using ASL's autopatch feature, enabling calls to VOIP phones to be made from a radio. This does require port 5060 to be open in the node's iptables (firewall) configuration and forwarded to the node in your router settings.

There are many cross-band full-duplex HTs and mobiles that are easy to find used for ~$150 or so.

Parts List and Component Options

Mobile-radio nodes are easy to build – only a MiniPC/RPi, URI, Radio, and a couple cables are needed. Recommended main components:

Dell Wyse 3040 MiniPCs have been used in probably 1,000+ AllStar nodes and work great due to their wide availability, low cost, simple set up, and reliable operation. Many have built-in WiFi cards and dual antennas, which work very well, though personally I prefer wired Ethernet whenever possible for maximum performance and less potential RFI. Many 3040's run on 5V 3A, but more recent "12V" versions will run on 5-16V. I've also seen new 3040's on ebay for a little bit more (~$60) which is a small price difference for new vs. used. But even a used 3-5+ year old 3040 should run very well for many years. The design is well thought-out with excellent thermal management and no fan to pull dust inside. If getting one that's more than a few years old I recommend checking the small backup battery and replacing it if below 3V. CR2032 batteries are available with solder tabs for as little as $1 ea. The case pops open with no tools needed and you can then also confirm if it has built-in WiFi. Many 3040's have the internal WiFi card and antennas even though many ebay sellers don't mention it. I usually have numerous 3040's with and without WiFi in stock that I can provide with new backup battery and ASL preinstalled at a reasonable price. I can also provide fully assembled and tested nodes.

Since the radio runs on ~12V, ideally the newer 3040 version that supports 12V input should be used. That way the 3040 can be powered from the radio's power cable and no AC Adapter or DC-DC converter is needed. The 3040 bottom label will say either 5V or 12V. The "12V" versions actually support 5-16VDC input.

For base-station or fixed location use ideally wired internet will be available and the 3040 will not need to support WiFi. Use of wired ethernet results in simpler configuration and higher reliability. WiFi may be needed in some cases though in which case the Dell OEM internal WiFi module works very well, or a USB WiFi adapter can be added which are anywhere from $5~$25 depending on range and performance.

Mobile Radio

Kenwood TM-V71A or Yaesu FT-8800 or 8900 mobile radios are the best options I know of for overall price, performance and features. These are often available on ebay, QRZ.com, eham.net, etc. for as little as $250 used to $400-450 new or near new. The hand mic supplied with the 8800R is not very good so for that reason I prefer the V71A, but that's a minor difference, and during normal node operation the mic is not needed.

Other radios can be used if they support Cross-Band Full-Duplex (CBFD) and have a "data" jack that provides unfiltered discriminator audio output and direct FM modulator audio input. However, many such radios do not support cross-band operation on the data jack, in which case the Mic jack can be used for Tx audio and PTT on one band with Rx audio obtained from the data jack, but this limits the use of the mic, ie. to switch between node operation and normal radio operation a mic switch would be needed, and, it does not support flat Tx audio where ASL's USBRadio driver can be used to provide CTCSS encoding and Squelch Tail Elimination (STE).

The Alinco DR-735T is the only current-production radio I know of that supports cross-band full-duplex, has a Mini-DIN-6 jack, has ≥ 4 stars average reviews on eham.net, and is easy to use and program via the front panel with no programming software needed, but it only supports the B band on the Mini-DIN jack thus for cross-band full-duplex the mic input needs to be used for A band node Tx on 2m, while the Mini-DIN provides unfiltered "9600" Rx audio on 70cm.

Radios such as the Kenwood TM-V71A and Yaesu FT-8800/8900 are much better options because their Mini-DIN-6 jacks fully support cross-band full-duplex thus with a single cable you have a finished node with proper STE in both directions as well as full use of the mic jack when needed.

When powered from 12V the fans on the 8800R and V71A run every time you key up (regardless of power level or transmit duration) and can be distracting in a quiet environment. If using the 735T on low power in a cool environment the lowest fan setting can be used (where the fan typically stays totally off if transmitting Low power), but the heatsink temperature should be monitored. A radio could be mounted inside a small case or Go Box with acoustic foam to reduce the fan noise and make the node more portable (with some openings at front and back to allow sufficient airflow).

Running radios on a lower voltage greatly reduces heat dissipation and fan noise. Many HTs will run very hot if powered from 9-12V but barely even get warm on 6-7V. Similarly, running a mobile radio closer to its minimum specified operating voltage results in much cooler operating temperatures and much less fan usage. The FT-8800R works great at only 8V, and at that voltage can transmit ~4-5 Watts for hours at 100% duty-cycle yet barely gets warm and the fan runs very slowly at most and is extremely quiet. This subtle detail enables very high quality nodes to be built that are also extremely energy efficient and quiet, simply by using a variable power supply or if using 12V batteries a step-down converter or voltage regulator. And when a radio or other electronic product runs at an optimal voltage resulting in near-zero heat dissipation it will last much longer and much less dust will be pulled in due to a fan running at high speeds. Very few hams are aware of how much of a difference in power dissipation and long-term reliability can be achieved simply by reducing power supply voltage.

If it was desired to build this node design in the most compact way possible, it can be powered from a ~$10 9V 3A AC adapter if the radio will used only in the Low (5W) power setting. Newer "12V" Dell Wyse 3040's also run fine on lower voltages and require well under 1A of current thus an ANF200 can be built using only a single small AC/DC adapter, MiniPC, the mobile radio and an HT antenna. Such a node would be almost as compact as the ANF101 design but with significant additional features. Use of an HT antenna can result in very high SWR if not properly set up and thus an SWR meter and solid ground plane would be advisable. A 1U steel rack shelf could provide an ideal chassis to mount everything to, including a small SWR meter and small mag-mount or bracket-mount antenna.

The DR-735T, TM-V71A and FT-8800R all support "9600" unfiltered ("flat") audio out which then enables the use of ASL's USBRadio driver DSP mode. This is easy to set up and provides high quality CTCSS/squelch detection and no squelch tails. I therefore recommend using only the 9600 output. This also simplifies the cabling and configuration because no COS line is needed.

The DR-735T Mini-DIN-6 audio input does not support flat audio however, thus the 735T has to do CTCSS encode rather than USBRadio. This works fine but means that USBRadio's notone setting cannot be used, which drops CTCSS prior to unkeying thereby preventing squelch tails on node transmits. Because of these limitations a TM-V71A or FT-8800R is highly preferable.

While there are many Chinese mobile radios available, as far as I know none of them provide a data jack with unfiltered audio or properly support cross-band full-duplex. (Some support cross-band repeat, but that's not the same thing.)

Cheap single-band radios such as old Motorola radios could be used but this doesn't really save much money, takes up more space, requires a duplexer or separate antennas, is more difficult to set up and configure, and does not provide nearly as many features as a good cross-band full-duplex mobile radio.

A Yaesu FT-8900R should also work fine, they have lower review ratings than the 8800R apparently due to some diodes often failing but they should be fine if used on lower power settings and at a reduced supply voltage. There are various other mobile radio models that should work well also such as a Kenwood TM-D710A or even a TS-2000, but these are more expensive and probably overkill for an AllStar node. And there are a number vintage/older radios that could work well but you'd want to carefully review the manual to confirm they have a Mini-DIN-6 jack that fully supports cross-band full-duplex operation.

USB Radio Interface

A number of URIs are available that use high-quality C-Media USB Audio I/O Controller ICs:

The recently introduced AllScan URI100 incorporates more thorough RFI filtering than any of the above URIs, with separated USB/Digital/Analog grounds and power, ferrite beads and bypass caps on all radio I/Os, optocouplers on the PTT & COS lines, and a 10Ω–500uF RC filter on the 5V Analog supply. The URI100 PCB measures only ~2"x2" in size - not much larger than a CM108 sound FOB but with far superior RFI performance and with all I/O lines available on through-hole pads in addition to K1 and 3.5mm TRRS audio jacks. The URI200 adds audio isolation transformers and extensive DIP switch configuration options supporting just about any possible grounding configuration with any types of radio(s), but the URI100 works extremely well with mobile radios and is a perfect match to their ~10KΩ audio output impedance.


AllScan URI100

Modified CM108AH on Left, RIM-LiteV2 on Right

AllScan URIs deliver unmatched audio quality, RFI-rejection and cost-effectiveness. Comprehensive LEDs show USB host Status, COS, ADC Clip, and PTT state. The URI100 is very easy to connect - when using USBRadio DSP mode only a TRRS to Mini-DIN-6 cable is needed which can be easily soldered together in about 5-10 minutes, or just cut a Mini-DIN-6 cable to your desired length and solder it to the URI100 internal 6-pin radio I/O header. For most radios using flat audio I/Os the TxAdj trim pot on the URI100 should be set to max (100% clockwise), and the RxAdj trimmer should be set to about 25% CW. Both SW1 DIP switches should be off.

After 100s of hours of testing with numerous URIs and radios over the past 2 years I am happy to report that the UCI100 has exceeded all my expectations, and is not only the best performing URI available for full-duplex mobile radio nodes (by a significant margin), but is also the most compact and cost-effective. At only $49 including a shielded enclosure and cables its value and performance cannot be beat. URI100 Schematic Diagram

The CM1xx-series ~45dB mixer gain range supports a wide range of audio levels while retaining the full dynamic range of the 16-bit converters. The ASL channel drivers set these gain settings in the IC based on the rxmixerset, txmixaset and txmixbset config settings.

RFI/Noise Optimization

Fobs or URIs that do not come with a metal case should be put inside a small aluminum enclosure to improve RFI resistance, protect the PCB from possible damage, and simplify the node appearance. A mobile radio transmitting as much as 50 Watts from a nearby antenna, or an HT used to talk to the node transmitting 1+ Watts from 5 or 10 feet away, can make for a challenging RFI situation – particularly with full-duplex nodes. Small opening(s) should be provided so the status LED(s) are visible, or mount standard 5mm LEDs on the enclosure and wire to the LED output lines on the URI.

All cables should be as short as possible, and the URI case should be grounded, which can be done by attaching a small (eg. #4 or M3) nut, bolt, washer, and star washer to the case and the radio's metal mounting bracket.

Setup Steps

Dell Wyse 3040 MiniPC

Installing ASL3 on a Dell 3040, other Mini PC, or Laptop/Netbook is not hard if you're experienced in building/maintaining PCs. The 3040's have a UEFI-only BIOS that needs a boot file in a specific place. Making a UEFI USB drive is simple: Download the amd64 ISO from debian.org/CD/netinst/, then format the USB drive as FAT32 and unzip the ISO into the root folder (7-Zip is a good program for unzipping ISOs). Do not try to make the USB drive "legacy bootable".

There have been rare cases reported where people were not able to properly copy ISO files to a USB drive but were finally able to get it working using "Rufus", a free program that can create UEFI USBs. It's probably not going to do anything that 7-Zip wouldn't but maybe it has fewer options and thus is more resistant to user error.

To initially set up a 3040 requires a USB keyboard and a monitor/TV with a DisplayPort cable. Plug in the keyboard and DisplayPort cable, and plug in the Debian 12 USB drive. Power up the 3040 and when you see the Dell logo hit F2 to enter BIOS setup. Some 3040's may have a BIOS password which defaults to "Fireport". This can be cleared in the Security section or if some other password was set can be cleared with a button on the PCB. Recommended BIOS settings: 

System Configuration
→ UEFI Network Stack: Disabled
→ Integrated NIC: Enabled (NOT w/PXE)
→ USB Configuration: Enable all checkboxes
Secure Boot: Disabled
Power Management
→ AC Recovery: Last Power State
→ USB Wake Support: Disabled
→ Wake on LAN: Disabled
POST Behavior
→ Keyboard Errors: Disabled
→ Fastboot: Thorough
Virtualization Support: Disabled

Nothing should need to be changed on the boot order page or any other pages. Once you have confirmed the BIOS settings, save and exit, and then when you see the Dell logo hit F12 for the boot menu, then select the USB drive. The Debian installer menu will then appear.

The Debian net install image is intended to boot on a removable device and install Debian on an internal storage device (or on a separate removable USB drive / SD Card). This differs from the RPi "appliance" image which goes on an SD Card, into the RPi, and the install is done. The Debian install takes about 20 minutes to complete. The default options should be fine but if there is anything you are not sure about, do a web search from another computer and try to clarify any questions you have.

The ASL2 image did not have the boot file where 3040's need it to be (/boot/efi/...), requiring an extra step to copy the boot file, but fortunately the Debian 12 installer provides this option.

I recommend the "high-contrast", "advanced" install option as it seems to better explain each step and not skip any potentially important details.

Installing on other Thin Client models or on a Netbook or Laptop should be even easier. (Note however that Chromebooks should be avoided, as ChromeOS is a closed and encumbered platform.)

A Desktop Environment such as MATE is a nice addition if you have a monitor, TV, or remote desktop app. This will greatly simplify wifi and wired network management but does require a 16GB 3040 version to fit everything.

GMKtek NucBox5 MiniPC

Installing Debian on a GMKtek NucBox is simple. First, make a UEFI USB drive by downloading the amd64 ISO from debian.org/CD/netinst/, then format the USB drive as FAT32 and unzip the ISO into the root folder (7-Zip is a good program for unzipping ISOs). Do not try to make the USB drive "legacy bootable".

Plug in a USB keyboard and a monitor/TV with HDMI cable into the MiniPC. The NucBox5 includes Windows 11. If you want to keep Windows you will want to let it boot and update itself (which can take over an hour) and then use the Windows Disk Management tool to shrink the C drive by 65,535KB, thereby leaving 64GB of unallocated space on the 128GB SSD. When setting up Win11 I recommend during the first time setup specifying that the PC will be used for "work". There is no need to create a Microsoft account. In reality it is unlikely you'd ever have any need for Windows on a node MiniPC, and with the 1+ hours of time it takes a new Win 11 install to update itself, keeping Windows is probably not worth the time and hassle.

Power off the MiniPC, plug in the Debian 12 USB drive, press the power button and you will see the Debian installer menu. (No changes should be needed to the MiniPC BIOS.) The Debian install takes about 10 minutes to complete. The default options should be fine but if there is anything you are not sure about do a web search from another computer and try to clarify any questions. I recommend the "high-contrast", "advanced" install option.

ASL3 Install

When the Debian install completes you will be prompted to remove the USB drive and power cycle the PC. Make sure it boots OK into Debian. The "hostname --all-ip-addresses" command can then be used to get the node's LAN IP address. You can then SSH into the node, proceed with the ASL3 install as described in the ASL3 Manual, and provision it on the allstarlink.org Web Portal.

ASL Configuration

ASL3 was released in July 2024 and is a major release that brings Debian and Asterisk up to the latest versions and makes other significant improvements. Asl-menu can be used to make some of the initial node configuration settings but the .conf files still need to be manually reviewed and edited as described below.

This node design can use hardware COS or USBRadio's carrierfrom=dsp mode. I highly recommend DSP mode to ensure the highest audio quality and eliminate squelch tails. While a short burst of loud white noise at the end of every transmission can give an "old-school" analog FM sound, squelch tails are in fact unnecessary noise that thereby decreases average signal-to-noise ratio. Any technique that reduces noise improves clarity and interactivity. There may be a tradeoff of a small delay (rxsquelchdelay in usbradio.conf which defaults to 30mS) in eliminating squelch tails but with this set to 10mS I still get no squelch tails and 10mS is a very short delay that should not result in perceptible outgoing IAX audio latency.

While most other node designs support only half-duplex operation often with a noisy RF module, no easy front panel programmability, closed-source software, overpriced RPi hardware, and/or limited features and configurability, AllScan node designs leverage the full capabilities of AllStar including advanced Digital Signal Processing, and only the best available amateur radio transceivers to deliver professional-level audio quality and a full feature set.

Mobile radios that provide COS eg. on a Mini-DIN-6 connector should have a cfg setting allowing the line to properly follow Tone Squelch rather than just Rx Busy, and most such radios should provide unfiltered discriminator audio out that supports Rx Carrier Detect and CTCSS decode in ASL. Be sure to only use a radio that supports at least one of these features, otherwise the node could get keyed up by QRM/QRN.

Tests I ran on a 3040 doing a full-duplex parrot test showed that the SimpleUSB driver and USBRadio driver in various carrierfrom modes all use about 10% total CPU, thus there should be plenty of headroom on a 3040 and no significant difference in CPU use between SimpleUSB and USBRadio.

rpt.conf Recommended Settings

rxchannel = Radio/[node#] ; Comment out all other rxchannel lines*
duplex = 3 ; Full-duplex, do not repeat Rx audio to Tx audio
hangtime = 100
althangtime = 100
;linkunkeyct = ct8 ; Comment out to prevent courtesy tones when connected
holdofftelem = 1
telemdefault = 0   ; Prevent "node X connected to node Y" messages
parrotmode = 1     ; 1 = Parrot On Command
;Uncomment following lines:
921 = cop,21 ; Enable Parrot Mode
922 = cop,22 ; Disable Parrot Mode

*In ASL3 there may be 2 rxchannel lines, one with dahdi/pseudo and the 2nd with Radio/[node#]. Those lines should not need to be manually edited. The ASL Menu Utility (run "sudo asl-menu" on the command line) should be used for initial node setup to set your node#, node password, IAX port number, AMI password, and channel driver (USBRadio).

usbradio.conf Recommended Settings

rxboost = 0
;Enter your desired Rx & Tx CTCSS Tone frequencies below
txctcssdefault = 127.3
rxctcssfreqs = 127.3
txctcssfreqs = 127.3
rxctcssoverride = 0
carrierfrom = dsp
ctcssfrom = dsp                 ; no,usb,usbinvert,dsp
rxdemod = flat                  ; input type from radio: no,speaker,flat
rxsquelchdelay = 10             ; delayline in ms carrier squelch tail eliminator
txboost = 0
txprelim = yes                  ; Audio processing on left output channel: no,yes
txlimonly = no                  ; Audio limiting with no pre-emphasis on output channel: no,yes
txtoctype = notone              ; Transmit tone control type: no,phase,notone
txmixa = composite              ; Left channel output: no,voice,tone,composite,auxvoice
txmixb = no
rxlpf = 2
rxhpf = 1
txlpf = 1
txhpf = 1
duplex = 1

NOTE: For radios such as the Alinco DR-735T that do not have a direct modulator (9600) audio input, use the following settings: 

txprelim = no                   ; Audio processing on left output channel: no,yes
txmixa = voice                  ; Left channel output: no,voice,tone,composite,auxvoice

Once you have set up your node and made the above settings you will want to run sudo /usr/sbin/radio-tune-menu and run these steps in the following order:

Some fine-tuning of these settings may be needed over time if you run into any issues where the node does not always reliably detect when you are keyed up. Refer to the allstarlink.org wiki or forums for more details on these settings. These settings are not well documented anywhere that I know of and there may be a better process for calibrating them than described above.

simpleusb.conf Recommended Settings

SimpleUSB is not recommended, but if you prefer a slightly "simpler" configuration or have issues with USBRadio, and have the COS line from the radio connected, the SimpleUSB driver can be used with the following settings: 

rxboost = 0
carrierfrom = usbinvert
ctcssfrom = no
deemphasis = yes                ; yes if using "9600" discriminator output, no otherwise
plfilter = yes                  ; yes if using "9600" discriminator output, no otherwise
txmixa = voice
txmixb = no
preemphasis = 1                 ; 1 if using "9600" modulator input, 0 otherwise
duplex = 1*

*In ASL3 the duplex parameter is not used in simpleusb.conf since it already exists in rpt.conf.

Audio Levels

Consistent audio levels and dynamics are important on any communication network, otherwise users have to make frequent volume adjustments to properly hear everyone. This is an issue on AllStar and I recommend that any time you hear someone who is significantly quieter or louder than average – let them know! Audio levels are easy to adjust on AllStar and there is no good reason anyone should have improper levels that require everyone else to ride their volume controls or put up with distorted, clipped, crackly audio.

Asterisk provides an AGC function that can be enabled in extensions.conf and this could be helpful if you find that nodes, repeaters, or nets you listen to have a lot of volume variation between different users.

Updating ASL

Be sure to review the ASL3 Manual and follow the recommended steps to periodically update Debian and ASL. After setting up any node I recommend checking the system logfile (in Debian 12 use "sudo journalctl", otherwise use "sudo tail -n 500 /var/log/syslog") periodically to make sure there are no error messages shown during system boot and normal operation. If you see an error (for which a web search of the message does not reveal a simple fix) check the ASL Forum to see if it has been reported, and if not I suggest making a new post.

Compiling ASL3 from source can help ensure you have the latest features and fixes and is a good way to learn more about how ASL3 works. This should not be attempted unless you have good Linux proficiency and experience with compiling C software.

Backups

When I build nodes I use Clonezilla to restore an image with the latest ASL, AllScan and various other utilities already set up. I then update everything and make a backup copy of the node before shipping. For instructions on how to backup and restore a node using Clonezilla see this post.

Wiring Notes

If powered from AC ideally a variable 12V 15+Amp DC power supply should be used, but if used only on the Low Tx power setting many mobile radios will be fine with as little as 9V 3A, and will then run much cooler and with much less fan noise. Ideally a "12V" Dell 3040 version should be used (which work fine on as little as 5V).

Power cords should be as short as possible and no more than one fuse should be used. Mobile radios often have power cables with 2-3 separate fuses, then another fuse inside the radio, and yet more fuses in the PowerPole distribution box/outlet. This results in as many as 5 fuses and 10+ feet of power wire, which over time often causes unreliable power connectivity and voltage drops. Therefore I try to keep radio power cords no more than 6 feet in length, with no more than one fuse in the cable (in addition to fuses I have in my power distribution box).

I recommend PowerPole connections for everything as these are easy to use and reliable. A PowerPole connector kit with crimp tool, insertion/removal tool, and various sets of connectors for different wire sizes can be a little pricey but are a good investment. Note that in addition to crimping, terminals should be soldered to each wire, otherwise wires can easily slip out of the terminals.

The above details will result in a nicely-integrated compact node with a single power cord.

If you happen to have only a 5V 3040, an LM2596 DC-DC converter or similar module can be used to reduce the 12V supply to 5V. In some cases though a few 1,000μF of added filter capacitance and possibly an RC filter may also needed to reduce switching-noise RFI.

Radio Interface Wiring

Kenwood TM-V71A, Yaesu FT-8800R, and Similar Models

High-quality radios such as the V71A or 8800R plug into a URI100 with a 3.5mm TRRS to Mini-DIN-6 (aka PS/2) cable, which are easy to make simply by cutting a cable to the desired length (12-16" should be fine) and soldering on a TRRS plug.

Wiring - URI100 to Kenwood TM-V71A or Yaesu FT-8x00 
TRRS Tip ------ Mini-DIN-6 pin 4 (9600 Rx Audio)
TRRS R1 ------- Mini-DIN-6 pin 1 (Tx Audio)
TRRS R2 ------- Mini-DIN-6 Pin 3 (PTT)
TRRS Sleeve --- Mini-DIN-6 Pin 2 (Ground)

Alinco DR-735T and Similar Models

The 735T and probably many older radios do not support cross-band full-duplex operation on the Mini-DIN-6 jack, thus the Mic jack has to be used for Tx audio & PTT on 2m while the Mini-DIN-6 supplies the 70cm Rx audio.

Wiring - URI100 to Alinco DR-735T 
TRRS Tip ------ Mini-DIN-6 pin 4 (9600 Rx Audio)
TRRS R1 ------- Mic Jack pin 6 (Tx Audio)
TRRS R2 ------- Mic Jack pin 4 (PTT)
TRRS Sleeve --- Mic Jack pin 7 (Ground) --- Ferrite Bead --- Mic Jack pin 5 (Mic Ground)

Other Radios/URIs

There are many other older radios that could work well but which can have a variety of different connectors and config settings. With the possible number of combinations of radios and URIs I can't cover them all here but it's usually easy to figure out from the radio manual and URI documentation.

Radio-Less Node Notes

See my other How-To Guide for details on building a high-quality full-duplex Radio-less node, which can be built with just a Dell 3040, CM108 interface and a half-dozen small parts.

With mobile-radio nodes that connect to the URI through a Mini-DIN-6 type of jack the radio's speaker and mic are still usable for normal radio use. The mic audio will only go out on the Tx RF (not into ASL), and only RF Rx audio will be output on the speaker (not audio from ASL). Thus the radio can be used as a normal radio any time (be sure you are not connected to any nodes if doing this, or turn off the 3040), but the mic and built-in speaker are not able to be used with AllStar. It would not be hard however to add a switch box that would switch the mic and internal speaker between normal operation and radio-less node operation, where the mic and speaker would connect to the URI instead of the radio. This could be complicated to set up depending on the specific radio, but could work well on Alinco radios since Alinco mics output regular DTMF rather than serial data. (I can do custom nodes with this and many other custom features, email me for details.) In the case of the 735T which requires the Mic jack to be used due to the data jack not supporting dual-band operation, a switch box could allow the mic and speaker to be switched between normal radio mode, node mode, and radio-less node mode. One ~6P3T rotary switch could be used to route all necessary lines.

Radio Settings

Be sure to set up the node with CTCSS Tone Squelch enabled, to prevent possible QRM/QRN from keying the node. And enabling Tone Squelch on your other radios will then shorten/eliminate squelch tails. Also check your local 2m and 70cm band plans (eg. in Southern California TASMA.org and SCRRBA.org) to find simplex frequencies specifically intended for analog FM hotspots so you won't possibly interfere with repeaters or calling frequencies.

Comments re. Frequency Coordination from Jim NO1PC: "...Hotspots are a 'new niche' not fully encompassed amid the more well-known realms of ATV, SSB, EME, repeaters, simplex, etc. Some regions have specifically addressed this, some not yet. "The ARRL Band Plan" is wholly inadequate in addressing this, but then they vacated much of the issue a decade or so ago. ... There are 53 repeater coordinating/spectrum management organizations in the United States. Links to them are provided by at least the following two web sites: https://w2xq.com/bm-repeaters.html, https://repeaters.us/"

When picking your node frequencies be sure to consult the above sources, and verify the frequencies are not being used by other nearby users or systems.

Alinco DR-735T Settings

Recommended settings for use with the 9600 audio output and USBRadio DSP mode

Kenwood TM-V71A Settings

Recommended settings for use with the 9600 audio I/Os and USBRadio DSP mode

Yaesu FT-8800R Settings

Recommended settings for use with the 9600 audio I/Os and USBRadio DSP mode

You should of course thoroughly read the radio manual and be familiar with all other menu settings and how to configure, store and recall memory channels.

Important Note: Nodes can run at a 100% Tx duty cycle during nets or long QSOs. Many radios are not designed for long-term 100% duty-cycle operation at Medium to High power and this could damage the radio. I suggest using Low power settings generally and only use Medium or High power if the radio has plenty of airflow and is in a cool environment. After first setting up any node the heatsink temperature should be monitored closely to establish what temperatures it reaches under various conditions ie. duty-cycle, Tx power setting, ambient air temperature, supply voltage, etc. If it gets hot to the touch an additional cooling fan and/or lower power setting is advised.

Ferrite Filters, RF Notes

Clip-on ferrite cores or ferrite beads are inexpensive and should be used on the audio cable(s), USB and ethernet cables. Laird 28A2029-0A2 work well and have enough room to allow cables to be wrapped 2 or 3 times. They are less than $1.50 ea. in Qty's of 10, and often come in handy for other things around the shack. One may be helpful on the power cable also depending on your specific setup and RF environment. Or you may be fine with no ferrites if your antennas are far enough away from the node. Ferrite kits can be found on amazon eg. with 50 pieces of various sizes 3.5–13mm for about $20. These are great for any ham shack and accommodate all common cable sizes.

Ferrite filters should generally be used with any DC power supply, with the cord wrapped around the ferrite a few times at the side of the cord closest to the power supply. Without that there can be significant buzz that comes through onto the node audio. This is a common issue caused by RF induced on the power cord causing 60Hz harmonics when the diodes in the power supply are near their zero-crossing points where they can be modulated by induced RF. This results in a broadbanded buzz on 60Hz and its harmonics that gets louder and quieter as you move antennas or cables around or move around with your HT that you're talking to the node with. This is not likely to be an issue on a high-quality mobile radio and power supply, but if it ever is, ferrite filters can reduce this by 99+%.

A ferrite filter is most likely needed on any ethernet cable going to the node, placed as close to the node as possible. A ferrite filter was needed with my RPi node on the USB cable, but on my Dell 3040 nodes no ferrite is usually needed there. This is good news as it confirms that the FCC-certified Dell puts out much less EMI/RFI than an RPi4. This is another advantage of the Dell 3040 (which has about 15 different certification logos on the bottom) over RPi's. But I often put a ferrite on the USB cable anyway just to reduce any possible chance of noise.

Everyone's RFI/EMI environment can be different. As with with any product or project, you may run into issues and need to do some debugging. You might need to add some extra ferrites on certain cables, or move some things around on your desk or in your shack. Any time a receiver is amplifying signals in the < 1μV range it's easy for interference to occur if you have a noisy power supply nearby, or you're too close to a cell tower, wifi devices, power lines, or other possible EMI sources. Keeping the node antenna as far as possible from other electronic devices is also generally a good idea.

Be sure to use a proper mobile or base antenna with large solid ground-plane and at least 25 feet of coax. HT-type antennas should never be used with a mobile-radio. They can cause RFI issues, have a high SWR, poor performance, and can overheat.

The antenna is the most important part of any ham radio system. If not properly installed and tested it could have a high SWR which over time could damage the radio or cause RFI and noise. Nano VNA analyzers are a great tool for checking antenna SWR plots and are easy to find for <$50 – which is quite a deal because 10 or 20 years ago the same thing would have cost easily 10 times as much. Or SWR meters can be found for as little as ~$25. Some nicer VHF/UHF radios even have a SWR meter function built-in. SWR should be periodically rechecked, especially with outdoor antennas that often corrode over time with exposure to the elements. And be sure to disconnect any outdoor antennas prior to possible lightning storms.

An important test to do after setting up any node is a sensitivity test where you transmit to it with low power from about a mile away, and using parrot mode confirm that your audio is clearly received. Also make sure your 70cm frequency is not a multiple of your 2m frequency. ie. if the node transmits on 145 MHz and receives on 435 MHz, it's not going to work. The 70cm frequency should be at least a couple MHz away from the 3rd harmonic of the 2m frequency.

Signal-To-Noise Ratio (SNR) Optimization

When building or optimizing a node it's important to measure the Signal-to-Noise Ratio of both the receive and transmit audio paths. This can be done by connecting the speaker output of any radio or receiver to a PC audio interface / sound card, recording the node's output audio, then normalizing the file to 0dB and looking at the noise level in the quiet parts. Note that SDRs are not recommended for this as they often have inconsistent results due to the numerous settings options they have with gain, bandwidth, and filter parameters, and they may have higher noise due to being USB-connected devices. A good quality analog radio is better for test purposes, and ideally should be run on battery power with no connections to any equipment other than the audio recording interface.

When you first assemble a node it might have perfect audio quality and no noise on both transmit and receive, in which case you don't need to test anything, but things are not always that simple. Consistently getting 55+dB SNR through the whole Rx + Tx signal chain on a node is not easy – especially on a full-duplex node. But once proper testing and optimization have been done the result can be indistinguishable from even the best Analog FM repeater systems. Mobile-radio nodes tend to have less noise/RFI than HT-based nodes since mobile radios typically use an outdoor antenna, and a $300+ mobile radio will probably have a better overall RF design than a $25 HT. Though HT nodes can sound just as good once properly optimized.

In having done extensive audio quality testing and seeing SNR's of anywhere from 40–60dB in various scenarios it was necessary to fully investigate all possible noise sources and optimize the design to ensure consistent results as close to 60dB SNR as practical in all cases. After weeks of testing, including building audio interfaces using various combinations of CM108B and CM108AH USB fobs, Repeater-Builder RIM-Lite V2's, audio isolation transformers, termination resistors, optocouplers, etc. I have things now pretty well optimized and consistently delivering 60dB transmit SNR (node transmit only) and 54dB round-trip full-duplex SNR (node and other radio simultaneously transmitting).

Full-duplex nodes are more of a challenge to minimize noise on because 5+ Watts are being transmitted (on 2m) while receiving on the same antenna (on 70cm), all while you're also transmitting into the node on another radio on 70cm. The following graphic illustrates SNR measurement results on a variety of nodes, radios and radio interfaces, along with S-Unit equivalents, and comparisons to typical audio equipment quality levels. Note that SNR is not the only important measurement of noise performance, as the type of noise and spectral distribution and randomness are also important, but SNR is one of the first things that should be tested in order to quantify overall clarity.

Measured Signal-To-Noise Ratios of various Nodes and Radios

60dB SNR on a node is a clean, clear, and professional-sounding result, easily on par with typical end-to-end Analog FM SNR's on even the best repeater systems. 60dB in real terms means that the noise is literally 1 million times lower in acoustic power than the signal, which equates to essentially zero discernible noise in typical listening conditions. (I will soon update the above table with SNR measurements on various mobile radios.)

For these measurements I record the node's transmit audio from the audio output of a high quality VHF/UHF base radio into a 24-bit audio interface, normalize the levels such that open squelch gives 0dB (max) signal level and no clipping on the interface, and then look at the signal and noise levels and noise spectral analysis in a wave editor (see Screenshot showing 60dB SNR during transmit hangtime after RXCD drop from an ANF101). In that case the ANF101 RT85's are capable of 60dB SNR thus we know that if the resultant SNR through the node is any less than that there is room for improvement.

Once the SNR is consistently above 50-55dB with the node operating Full-Duplex it will sound very clear, with no background noise audible unless you are in a quiet room and turn the volume up fairly loud. At that point there can in some cases still be some faint digital noise, usually comprised of harmonics of 60Hz and 1KHz from power supply and USB connections. Even at a low level this can be somewhat distracting/annoying, even more so than quiet broadband white-noise that might be 10+dB louder. Thus whenever building a node I ensure all such noise is properly fixed, which can require a lot of testing and optimization but becomes easier once the SNRs, gains, and source and load impedances of the node components have been properly measured and characterized. If you usually use a node in a mobile or loud environment you would probably be just fine with a 30-40dB SNR, but for quieter home/office environments closer to 60dB is definitely preferable.

Node Management

Installing AllMon and then AllScan is highly recommended. AllScan provides a Favorites Dashboard with integrated ASL Stats scanning. This makes it easy to add favorite nodes and see their Tx & Rx activity and Connected Link Count stats in real-time (typically 1-minute resolution). These apps can be used in any web browser.

AllScan Favorites Management & Dashboard Web App

Wi-Fi Support, Portability

Wired-internet is more reliable and easier to set up but for a portable node wireless connectivity is essential. USB WiFi adapters are inexpensive and fairly easy to set up if you have basic familiarity with Linux.

Many 3040's come with an internal WiFi card and antennas that work well. Otherwise a cheap USB WiFi adapter should work for short-range communication but I would recommend a reputable brand that's known to work well on Debian Linux and that has a proper antenna. With WiFi frequencies starting at 2.4GHz, a 1/4λ vertical antenna should be 3cm in length or for some gain you'd want 1/2λ or 5/8λ ie. 6-7cm antenna length. Any adapter that's smaller than that is probably not going to have good performance. The TP-Link "Archer T2U Plus AC600" look good and are < $20. I would suggest testing a few different models and seeing how their signal strength, jitter, packet loss, etc. are at different distances from your WiFi router.

AllStar and other VOIP / communication applications require low-latency, reliable IP connectivity, and extra care is required to ensure any WiFi devices and networks used are properly set up. If you ever experience audio issues, dropouts, jitter, etc., it is much more likely to be an issue with your network configuration than with ASL or the node itself.

If you use WiFi on a node you should have basic familiarity with Linux and configuring the various settings. Eventually some setting or driver may need to be updated or debugged. Like anything with computers this is not hard to do, just do a web search for what you want or what issue you're seeing and dozens of web pages with plenty of answers will usually come up.

Wi-Fi Setup for nodes with no Desktop GUI (Command-line Only)

This Article has detailed instructions on how to set up WiFi on Debian. This process does require knowing the node's IP address (which can usually be found on your router management page) and initially connecting to the node through ethernet with an SSH app. This may not be easy to do on networks that you do not manage but there are ways to make that easier, for example you can set up a command in ASL to say the node's IP address in response to a DTMF command. On all nodes I ship I have DTMF commands *690 and *691 set up to say the node's LAN and WAN IP addresses. See the AllScan FaceBook Group for details on how to set up these commands, plus many other tips and updates.

Before configuring WiFi as described in the above article you may need to run the following steps: "sudo su", "apt install wireless-tools net-tools wpasupplicant", then run "iwconfig" and confirm a wireless interface is listed. On a Dell 3040 with internal WiFi module this shows a wireless interface named "mlan0". You may then need to run "ifconfig mlan0 up" to start the interface. "iw mlan0 scan" should then list the available networks, or run "iw mlan0 scan | grep SSID" to see just the names.

After first setting up WiFi on a 3040 I was seeing a lot of jitter and audio dropouts but after disconnecting the ethernet cable, restarting my WiFi router and restarting the node, everything worked perfectly.

Another way to set up WiFi on Debian is with iwd, which may be slightly simpler vs. the article above. See this Article for details.

Wi-Fi Setup for nodes with a Desktop GUI

To simplify WiFi network management a Desktop Environment (DE) can be set up on the node such as MATE along with a small LCD monitor and USB keyboard/trackpad – or use an inexpensive Netbook or small Laptop instead of a MiniPC. Connecting is then as simple as clicking on the network icon and selecting the WiFi network. The DE should then be configured for auto-login so that WiFi will auto-connect after bootup without needing to turn on a monitor and manually log in with a keyboard.

Some DE's may be able to automatically connect WiFi only if ethernet is not available, but it seems MATE does not have that option. This Post shows how to set up a Network Manager script that automatically turns Wifi off or on when ethernet is or is not available, which should help ensure WiFi is not left on when not needed.

If you often travel and connect to various WiFi networks, using a small laptop or netbook for the node computer rather than a 3040 can make things much easier to manage. These are available for around the same price as 3040's which is a quite a deal considering they include an LCD, keyboard, trackpad and battery. I have used a small Asus netbook that came with Linux Mint preinstalled (was only $50 on ebay) and it works perfectly. This makes for an innovative node product that in addition to being an AllStar node works as a regular laptop and runs 1,000's of free programs available on Linux. Small laptops are slightly more expensive but still < $100, and have a nicer keyboard, more I/Os, and better performance.

For my ANR100-LT nodes I use Dell E7440 laptops, which are easy to find for < $100, with 256GB SSD, charger and Win 10 Pro. They are nice compact laptops with backlit keyboard, full HD LCD, and decent battery life. I shrink the C drive by 65,535 MB and install Debian 12 on the blank partition which then sets it up to dual-boot either OS with Debian and ASL3 as the default. ANR100-LT Demo Video

Full-Duplex Communication Benefits

All AllScan nodes and products support full-duplex communication, which provides powerful advantages over half-duplex nodes. This requires setting the "duplex" parameter to 3 in rpt.conf and to 1 in simpleusb.conf/usbradio.conf. If you do not do this you will not hear Rx audio when keyed up and will be much more likely to experience doubling and other issues.

In The Beginning...

In the beginning...there was CW. Most HF/CW/All-mode transceivers support full or semi break-in keying, meaning that the receiver is on between symbols/letters/words sent. Thus if someone is transmitting on a decent radio and making a reasonable attempt to monitor the frequency between characters or words, anyone can easily break in. Thus CW supports interactive, fluid conversation, and allows others to join a QSO or reply to a CQ at any time. CW can be considered semi-duplex because each dit and dash is only a couple 100mS and good radios can switch between Tx and Rx very quickly. Thus the receiver is never off for a significant time and it's easy to hear responses and other activity on the frequency.

And then there was AM, and soon after SSB which is much more energy-efficient and more widely used. Because SSB has no carrier there is no energy transmitted (or very little) during quiet parts ie. between words or during pauses. Experienced hams take advantage of this by briefly unkeying here and there, during pauses or maybe every other sentence, for enhanced awareness of the channel. This is a subtle technique that many aren't aware of. Some operators will just key up and talk for minutes straight, whereas more experienced OMs tend to keep things shorter and more interactive – just like in-person conversations. When you talk to someone in person you don't just talk for 3+ minutes straight at a time without ever pausing to allow someone to comment, acknowledge, reply, etc. And there's usually no good reason to do this on the ham bands, with some exceptions such as on nets. Thus while SSB is not generally full-duplex, experienced hams use it in an interactive way where they pay attention to what's happening on the frequency (as well as plus or minus a few KHz where there might be QRM or QRN that needs to be worked around), and as a result QSOs tend to be more dynamic and interesting.

And Then There Was FM

Next there was FM. FM sounds better than AM because of its better noise resistance, but it is less energy efficient than SSB due to having a constant power regardless of modulation level. And unlike SSB where you can unkey briefly with no audible effect, if you unkey on FM it results in squelch drops for listeners (unless their radio has unusually good squelch or they have tone squelch properly set up), thus there is a slight disincentive on FM to pay attention to the channel while you're transmitting.

Due to the FM capture effect, multiple people can't transmit at the same time or the signals interfere destructively or one covers up the other. With SSB that's not an issue and multiple signals combine linearly. One might be louder than the other or you might not be able to follow what either is saying very well but at least you'll be able to tell that there are 2 people talking, vs. FM doubling which can sound like a train wreck. Thus when FM first started being used on repeaters 60+ years ago it sounded great but also had some limitations that earlier modes did not.

As a side note, repeaters don't need to only use FM (or PSK digital equivalents). They could also support SSB without a huge amount of effort. Squelch would be a little more complicated because you don't have a constant carrier to reference, but DSP, signal analysis, noise reduction and AGC techniques have come a long way since the days of the first FM repeaters. It would not be hard to set up a repeater with separate FM and SSB inputs and repeat the audio on separate FM and SSB outputs. This would for the first time (that I know of) enable the advantages of SSB to be achieved on a repeater, namely SSB's inherent resistance to destructive interference and thus the ability to support multiple signals on a single frequency, and SSB's greater power efficiency that would reduce battery use for portable users or give more range with the same average power.

Before the Above There Was The Telephone

Originally repeaters and radios only supported half-duplex (from the user perspective). If you receive at the same time you're transmitting, from a repeater that has only one FM receiver, you're generally just going to hear yourself, or maybe a bunch of noise if someone doubles with you. Technically a repeater is full-duplex because it can transmit at the same time it's receiving, but that doesn't do you a lot of good (beyond the basic advantages that repeaters provide) if no more than 1 repeater user can transmit at the same time. Prior to ASL, only rarely did repeaters actually support true multi-user full-duplex communications. This is in contrast to phones which are multi-user full-duplex and always have been, which is much more natural and intuitive. Even the very oldest telephones from the 1800's were full-duplex. Apparently Thomas Edison and whoever else contributed to the early development of telephones figured out that it would be easier to just let people talk whenever they want with no limitations on how many people can talk at a time. This is easier to do on a pair of wires than over RF, but can be easily done on RF by using multiple bands/frequencies.

Multi-User Full-Duplex Repeaters

Most repeaters have only one FM receiver, which due to the FM capture effect can only properly receive one signal at a time, thus there was really no such thing as a repeater where any number of people could talk at any time while also hearing everyone else. To support that without ASL currently requires a repeater to have multiple receivers. Such systems do exist and work well for trivia nets or other scenarios with quick-witted hams jumping in with quick comments. San Diego's W6ZN repeater does this and there are numerous interlinked repeater systems with multiple inputs such as the SoCal DARN or PAPA systems where you can listen to one repeater on one mountain and transmit into a linked repeater on another mountain. ASL now makes it much easier for repeaters to support true multi-user full-duplex, as connected (radio-based) user nodes in fact extend the repeater with additional receivers and user-specific link monitoring transmitters (ie. that do not repeat local Rx audio).

And Then There Was The Internet

The Internet is essentially an extension of public telephone systems that had existed for a century before, with the major difference being packet-switching vs. circuit-switching. They both work for getting audio from one place to another regardless of if it's half-duplex or multi-user full-duplex. The internet does this in a general way with no limitations on the application layer which is a big improvement over the closed and proprietary phone system networks that have now become mostly obsolete.

And Finally There Was Asterisk and Then AllStarLink

Because ASL is based on Asterisk – a phone system, it supports full-duplex perfectly and makes it very simple. Even repeaters that have only one RF input, that would not ordinarily support multi-user full-duplex, if ASL-linked now support this capability by default for all AllStar users. I have tested this on many repeaters and it works just like a full-duplex phone call on a speakerphone. You talk just like you would on a simplex node but if someone else keys up you hear them and if someone doubles you hear it right away. Because you always hear the remote system, and if someone starts to double or there's echoes, timeouts, interference, etc. you can simply unkey until the repeater (or node / hub / bridge / etc.) is clear. This is a powerful feature that greatly improves the interactivity, efficiency and flexibility of amateur radio repeater communications. And it's an essential feature in emergency comms scenarios.

For those who have not used a full-duplex radio or node, or who do not intuitively understand how much of a difference it makes, a simple analogy is to consider what it would be like if the phone system was only half-duplex. Imagine that when calling a friend, relative, or business if only one person could talk at a time, no one could speak until the other person or people on the call unkeyed, and if when you then did key up to speak you couldn't be sure someone else hadn't keyed up at the same time. This would result in awkward and inefficient conversation because it would no longer be like real in-person communication. In contrast, full-duplex enables natural, smooth, effortless communication just like when you're standing right next to someone.

True Multi-User Full-Duplex

Although most people may not know it (even repeater owners), ASL-linked repeaters by default do support true Multi-User Full-Duplex. This is a subtle detail that can be hard to fully appreciate until you've tried it yourself. The repeater itself on analog will not support more than one analog RF input at a time if the repeater has only one RF receiver, but generally will support any number of simultaneous ASL full-duplex users and at least one analog RF input. There are a small number of improperly set up repeaters that don't support multi-user full-duplex but I only know of a few.

By default when a repeater links to ASL it will be with a node whose audio output gets mixed with the RF receiver audio input(s). Some repeaters may prioritize one over the other and only allow one audio channel at a time, or ASL may be linked through some intermediary interface, but even then multiple connected AllStar users can still be full-duplex and talk and hear each other fine, as that's a core feature of Asterisk's architecture. Audio streams from each connected node are always routed to all other connected nodes, no different than a VOIP conference call.

Some repeater system admins may opt to give RF Rx audio priority over AllStar Rx audio but there is no advantage to this and it only causes issues. For example if an RF user and an AllStar user key up at the same time the RF users on the repeater will hear only the RF user while AllStar users hear only the AllStar user, thus resulting in 2 separate conversations, which makes for quite a dysfunctional system. Such a phenomenon could be called "halfing" rather than "doubling", as it results in the communications topology being split into separate halves while both users are keyed up. Fortunately only a small number of repeaters seem to have this issue. If you should encounter such a system I suggest letting the admins know there is a better approach, ie. combine (mix) the Rx audio inputs rather than prioritize one over another.

Amateur vs. Professional

Go on any repeater net that has more than a half dozen or so users and you'll frequently hear doubles, quick-keying, and other issues, which can waste minutes of everyone's time, result in inefficient communication, and could even be described as "amateurish". Full-duplex solves these issues and gives you full situational awareness. This goes back to the definitions of "amateur" vs. "professional". Amateur just means it's not for-profit – not that we can't communicate well. Full-duplex enables communicating as if you were standing right next to everyone in the QSO, and AllStar makes this so easy to do that there's no reason not to.

Situational Awareness

Another nice detail about full-duplex is that once you start transmitting from your cross-band full-duplex HT it's nice to see your node transmitting back to you right away. I can be over a mile away on an HT and start transmitting, its red Tx LED lights up, and then ~25mS later you see the green Rx LED light up which confirms that you're in range, the node is receiving you and transmitting back to you, no one is doubling with you, and you hear if there is any path noise. This is another example of how Full-Duplex improves overall situational awareness.

Radio Compatibility

Cross-band full-duplex nodes are fully compatible with half-duplex radios if they are dual-band dual-receive. For example a Kenwood TH-D74 I used to have won't do full-duplex but I had the node's 70cm Rx frequency on one memory channel and the 2m Tx frequency on the next memory channel, with dual-watch on and when I transmit the D74 will not receive at the same time but once you unkey you hear the node transmitter just fine. Thus any dual-band dual-receive radio can be used, which pretty much all modern HTs are.

Full-duplex nodes provide powerful benefits even if your other radios are only half-duplex. You can key up any time without having to wait for the node to unkey first, and if during a transmit you quickly unkey on a half-duplex radio you'll immediately hear what's on the remote system and can confirm that the channel is clear and no one is doubling with you then key up again. This is essentially the same technique mentioned above used by savvier hams on CW and SSB since the dawn of those modes, and makes checking into larger nets more efficient and enables large QSOs and nets to run more smoothly and interactively.

Full-Duplex Nodes vs. Repeaters

A Cross-Band Full-Duplex personal node (ie. that has duplex=3 in rpt.conf) does not repeat receive audio into the transmit audio. This is an important distinction and I do not recommend that this node design be used as a repeater or in a commercial application. A common misconception is that a full-duplex node is a repeater. This is not a valid assumption, and building a repeater is not the subject of this guide.

A full-duplex personal node can be used as a repeater (by setting duplex to 2 or 4 in rpt.conf), but that defeats one of the main benefits of a full-duplex personal AllStar node – the ability to hear audio from other connected nodes at all times without your own outgoing audio being repeated back, and thus no need to use a headset or headphones. This gives much better situational awareness and flexibility than a simplex node because if someone else keys up while you're talking you hear it right away and can then unkey thereby preventing a double, or you can both continue talking. In that case the conversation can work just like a good quality speakerphone. ASL is based on Asterisk – an enterprise-grade phone switch system that supports full-duplex by default for all users, thus anyone can key up with a quick comment or break any time. There are applications where a small low-cost portable repeater is useful though, such as if traveling with other hams to a remote area or field day site. For occasional repeater use this node design works well and provides all of ASL's features at a very reasonable cost.

Because the Tx audio is not repeated a personal node is generally limited to one RF user, in contrast to a repeater which can be shared by numerous users, but a personal node can be used by multiple RF users if they are all within simplex range of each other and thus can all hear each other's transmit audio. Cross-Band Full-Duplex (CBFD) radios also support dual-receive, thus when receiving you can monitor the node input and output frequencies at the same time. Thus if you have 10 ham friends within a few miles who all have CBFD radios, you can all use one CBFD personal node and hear all local RF users on the node input frequency and all ASL users on the node output frequency. This will not prevent doubles if 2 RF users key up at the same time, but that shouldn't be an issue if you use the node at different times or have only a few people using it at the same time who are careful to avoid doubles.

(Ideally a radio supporting CBFD could be set up with echo-cancellation DSP functionality, in which case any number of users could share a CBFD repeater node and each radio could subtract its transmit audio from the receive audio. Echo-cancellation is used in telephone and VOIP systems to help prevent echoing/feedback. No such radios currently exist, but it wouldn't be hard to build one. Maybe someday an open-source Linux-based HT product will be created that supports CDFD and runs GNU Radio or other SDR programs enabling DSP capabilities. This could be a very popular product as it could then also support other analog and digital modes and anyone could create their own software, DSP algorithms, codecs, etc. or even whole new analog, digital or hybrid modes.)

Repeaters are therefore full-duplex in a different way than full-duplex personal nodes – a Full-Duplex personal node supports one or a small number of nearby users, whereas a Repeater supports multiple users over a much larger area who usually have only half-duplex radios. A full-duplex radio (or 2 half-duplex radios) are commonly used with repeaters, particularly by net controllers, however in that case because the Tx audio is echoed back a headset or headphones usually need to be used to prevent feedback/echoing, and there also can be a delay in the repeated audio on some linked repeater systems which makes the full-duplex aspect from a user perspective not as user friendly as full-duplex on a speakerphone or full-duplex personal node.

Building a half-duplex node is slightly simpler and less expensive, but even if you do not yet fully understand or appreciate the advantages of full-duplex there is no disadvantage to supporting full-duplex and you will then have a higher-quality node that will be a better long-term investment.

Summary

There are no disadvantages to full-duplex other than slightly increased cost, which is a small price for all the above advantages. This node could be used half-duplex if desired though, just select the B band as the Main band on the radio and change the duplex settings in rpt.conf and usbradio.conf.

Kenwood TS-2000's are excellent All-Band All-Mode radios supporting Cross-Band Full-Duplex


Demo Video & Shootout with 7 Different Cross-Band Full-Duplex Radios


FAQs

Q: I like the idea of Full-Duplex but I have to wonder wouldn't I get a lot of feedback? When I use Full Duplex on satellites I need earbuds.

A: The great thing about Full-duplex on AllStar (with duplex=3 in rpt.conf, not 2 or 4 which is a repeater), is that it does NOT repeat your Tx audio into the Rx audio that goes back to you. Thus it's no different than talking on a speakerphone – you hear the other people on the call but it doesn't feed back your own audio. Because of this, Full-Duplex is actually much easier to use on AllStar than it is on satellites or non-ASL-linked repeaters.

Node Notes / Instructions

I provide the following notes with nodes I build and have included them here as they are useful notes regarding the general operation of any AllStar node.

  1. When you first plug in the node and connect an ethernet cable, it should be assigned a DHCP address by your router. If you look on the router's web admin page it should show a list of connected devices and the IP Address assigned to the node. You should then 'reserve' that address for the node there so the IP Address does not change later. The *690 DTMF command can also be used to have the node say its LAN IP address, or *691 for the WAN address.
  2. You'll also need to then forward port 4569 UDP&TCP in the router to the node. If this is not done you may get jittery audio or dropouts. (This assumes you do not already have another node on port 4569. Otherwise subsequent port#s should be used ie. 4570, 71...)
  3. If you will want to use AllMon/Supermon/AllScan from external networks you'll also need to forward port 80 TCP in the router to the node, or for portable nodes use a Dynamic DNS service.
  4. To access the node by SSH enter the node's IP Address in your SSH client, username=______ and password=______. This password should be changed. To do this, log into the node by SSH and type "passwd" and you will be prompted for a new password. Make sure not to lose that as there is no easy way to recover or reset it.
  5. AllScan and AllMon are installed and have the same login: username=______ password=______, and can be accessed by entering the node's IP or DDNS Address in your browser. To update the AllScan password go to the Users page link. To update an AllMon3 password see this link. To update an AllMon2 password see this link. To update a Supermon password see this link.
  6. If the Dell 3040 has not been connected to power for awhile sometimes the power button has to be held in for 5-10 seconds and it may take a minute to then start up. Usually though a single click is all that's needed to turn it on or off.
  7. AllStar nodes can take several minutes after first being turned on to register with the ASL Network and for connections to remote nodes to then be accepted.
  8. The radio is set up to RX on 431.18 MHz and TX on 147.48 MHz, with a 127 Hz PL. This can be easily changed on the radio. Be sure to confirm that the frequencies are not being used by any repeaters or other reserved frequencies in your area.
  9. The mobile radio can be left off if using IAX/SIP apps instead of a radio.
  10. Because 5+ Watts of RF is a significant amount of RF power that can easily induce EMI/RFI on nearby electronics, it is highly recommended to use only a high-quality outdoor antenna that is at least 25 feet above ground, and at least 25 feet away from the node, from any other electronic devices, and from people and pets. This will also greatly increase range.
  11. RX and TX level adjustments can be made in the asl radio tune settings, by logging in by SSH and running "sudo /usr/sbin/simpleusb-tune-menu" if using simpleusb driver or "sudo /usr/sbin/radio-tune-menu" if using usbradio driver, then follow the prompts to adjust the level settings.
  12. You can check your audio using Parrot mode: Enter DTMF command *921 to enable, *922 to disable. (Be sure you're not connected to any other nodes when doing any testing.) N2DYI's Parrot Test Node 55553 can also be used. When setting levels keep in mind that it's better to be a little on the low side than to have too much gain and possible clipping and distortion.
  13. The audio levels on the node have been adjusted to good general levels, however your voice and your radio(s) you use may be louder or quieter than average and you may need to adjust the Rx gain accordingly. You can also adjust the Tx gain to your personal preference or to better match its audio levels with local FM repeaters.
  14. An extra ferrite filter is included in case you get noise/RFI on the node or in any other devices. This should not be needed but if you do get any noise try putting it on different cables to filter out noise and help locate the source(s).
  15. For nodes with wifi, it is generally recommended to use wired ethernet when available for best performance. In this case the wifi module should be turned off with the SSH command "ifconfig mlan0 down" or DTMF command *692, and can later be turned back on with the command "ifconfig mlan0 up" or DTMF command *693. The wifi will default to on when the node is next powered on or rebooted, unless this is changed in the networking settings.
  16. If you have questions on the node or settings be sure to review this guide, which is frequently updated.

Troubleshooting

If there is any noise on the node's transmit or receive audio these are some simple solutions:

  1. Check the power supply ripple, try different power supplies, and added ferrite filters. A snap-on ferrite core filter with 3-4 turns of the DC power cable around it is often helpful – as close to the power supply as possible.
  2. To prevent any possible ground loops, keep all wiring as short as possible and always run power and audio wires/cables in straight lines and next to each other rather than spread apart or in any shape resembling a loop. Also be sure to use only a star-ground configuration such that there is no more than one ground path between any 2 node components.

If you get distorted audio or stuttering/dropouts, or inbound connection attempts to your node do not work, make sure all your port settings match on the ASL site for both the server and the node, and that those match the port settings in iax.conf (bindport), rpt.conf ([node#] = radio@ip:port), in the node's firewall (iptables) configuration, and in the router/cable modem. This is 6 different places the port has to be set. If it's your first node then you probably have the default of 4569 and didn't need to change anything, but if it's not your first node then a different port number is required (eg. 4570, 4571, ...), and all 6 of those places need to have the same setting. The node can still appear to be working fine if those settings don't match but the audio will be more likely to have stuttering/dropouts.

Conclusion

My goal has been to find the simplest and most cost-effective ways to build a full-duplex node using only high-quality off-the-shelf components. I also build and sell fully assembled, configured and tested nodes. For more info see the Products page.

Contact

For any questions, feedback or other enquiries email david at allscan.info.

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