Forth Estuary Experimental Data Network

Network Map
Status 2 day
Status 30 day
Technical Info
Contact Information
Feednet Services


Downloadable PI Image


Most of what can be achieved via FEEDNET is courtesy of open source software. The sheer hard work, altruism and inventiveness of all open source authors is gratefully acknowledged here.




USBtran - RoIP Remote VHF (UHF) Base Station.

Bernie McIntosh, GM4WZG - March 2016.

What is USBtran ?

USBtran is a VHF FM transceiver that has a USB port which plugs into a computer, such as a Raspberry PI or a PC.  Using the Asterisk VoIP system, the VHF channel can be linked to other similar units on the other end of a network connection.  This connection could be an independent one implemented by radio amateurs such as  FEEDNET or it could be a standard Internet connection point.

VHF users can talk to other VHF users or to VoIP telephone users.

USBtran provides, in one unit, a replacement for both the standard soundcard/PTT interface and the transceiver itself in a typical Allstar Node. It partly came about because the supply of the commonest hardware interface for these nodes has dried up and partly because the DRA818V module looks pretty neat and is worth trying out.  I am not disappointed with the results.

See below for details on how to make your allstar node into a wifi access point.

What does it do ?

  • Using a small and simple antenna you can provide a VHF point of access around the house/grounds which allows you to access other similarly equipped Asterisk nodes, some of which may be on the end of an internet connection in another continent, others which may be on the end of a FEEDNET wifi link.

  • Just like in (1) above but if you use an effective external antenna and maybe an amplifier you will have a system where technically, everything works the same way as described above, but now you have extended the range to cover more distant places and amateurs other than yourself. You may need a NoV to use it like this.

  • Use USBtran to allow one or more mobile telephone users to access VHF radio when they run VoIP apps on their Android or Apple devices.

  • Make use of the DTMF capabilities of an Asterisk server to provide  remote control either from the radio channel or from the VoIP telephone channel.  DTMF is used to run programs. Programs can do things on the PI itself, on relay boards connected to it or even over the internet,

  • Use the USBtran as a remote listening receiver to record everything it hears on the channel

  • In addition to recording the channel, you can stream the audio  to several listeners. Include a delay if you want - this will facilitate the trapping of accidentally sent confidential information during an emergency support incident.



  • 130-174Mhz transceiver based on Dorj DRA818V.  

  • Transceiver is programmable via the USB connection.

  • 27dBm or 30dBm switchable power out.

  • Additional 7 pole Butterworth low pass filter for clean output.

  • CTCSS on both send and receive can be programmed.

  • USB 2.0 port for connection to computer.

  • Powered by the USB bus - no other power required.

  • Protected by resettable fuse.

  • Audio amplifier and high level 8 ohm speaker connector for local channel monitoring

  • Isolated (diode protected)  PTT out connector for triggering external amplifier change-over relay.

  • Switching and breakout of signal paths to connect Rig PTT , COS, low-level audio in, low level audio out to an external transceiver.  In other words, you don't have to use the built in transceiver, you can just use the USBtran as a standard Asterisk aptRpt soundcard interface.

  • CM119 or CM108 Sound Chip. Designed to be plug and play with Asterisk Apt-Rpt.

  • Half Size Eurocard. Slots into a standard case.

  • On board LED status indicators. TX, SQ, TxD, RxD, Soundcard active.



It is possible to substitute the VHF module for a UHF module in this transceiver. The Low Pass filter would need to be substituted also.

Are these boards available for sale ?

I've already been asked if these transceivers are available for others to purchase.  It kind of looks like a "product".  Right now the answer is no.  This was a fun project and I happen to like making things look like a decent product -  nothing more!

But if enough folk really were interested I could get a local PCB assembler to to make up a batch of boards - maybe 100 or so, with a view to folk paying cost price plus a small amount for contingency. An alternative could be to just make some bare PCBs available.   Write to me if you are interested in either option. There are other products out there and its quite easy to modify a soundcard, or even make a board like this, but if there is sufficient interest I will let you know and put an update here.

How do I find out about the software ?

I thoroughly recommend Doug Crompton's web site. Doug, and many others, have given huge amounts of their time and effort in the production of software and images that are easy to use just by following instructions.  Inspirational, and a perfect demonstration of the true spirit of Ham Radio.

How to put a WiFi access point on Doug Crompton's PI 2/3 Image.

This allows you to connect a mobile telephone, for example,  to the PI to operate Asterisk and the USBtran. I'm not too familiar with ArchLinux but after figuring a few things out and going down a few blind alleys this wasn't too hard. Maybe I can make someone else's journey a little quicker. I used Doug's v1.02

First login as root.

Make sure you do a full system back up using whatever method you prefer and have confidence in.  Your system may be different to mine and you may lose any or all of your working system.

There  are a few packages need to be installed:

First - iw, a tool to show / manipulate wireless devices and their configuration

# pacman -S iw

Now wpa_supplicant - a tool that allows you to use authentication on wifi networks

# pacman -S wpa_supplicant

hostapd is a software access point daemon

# pacman -S hostapd

We use dnsmasq to provide dhcp services to the access point. Without this you can't issue a device connecting to your access point with an ip address/.

# pacman -S dnsmasq

Nettle seems to be needed. I don't know much about it - seems to be a cryptographic library.

#  pacman -S nettle

Here is a wonderful access point tool that can save you hours of configuration work.   Download and install it.

# git clone https://github.com/oblique/create_ap

# cd create_ap

# make install

 That's it. A reboot might be sensible although probably not needed.

To create an access point once, from the command line

# create_ap -n wlan0 myaccesspoint mypassword


If you check with a wifi enable device you should see the wifi ssid myaccesspoint. Connect to it and give it the password mypassword.

Any error messages will appear on the screen.


Read the documentation for create_ap at   https://github.com/oblique/create_ap

You can use systemctl to enable your access point on every reboot. First edit your service file to configure it the way you want it.


#cd /usr/lib/systemd/system

# vi create_ap.service

#systemctl start create_ap

# systemctl enable create_ap

There are lots and lots of options - you can have the PI connected to two subnets simultaneously for example.  You can bridge or NAT the interfaces.

Things to do

When we make a few more of these I will be including a small 20mm x 20mm fan on the Dorj module. The rear heatsink of the module is soldered onto the board which helps to dissipate heat.  I think for long term continuous duty cycle use it might be reassuring to have just a touch of air movement to help with cooling.


Folk often say that SMD work requires too much specialist equipment and are dissuaded from trying it.  Don't be! This board was created using free Designspark PCB software. Etched by Eurocircuits. Assembled by hand with nothing but a Weller soldering iron that I have had since 1979, and a cheap Atten 858D hot air station. I do use a hot plate at times made from a slab of aluminum which is handy for keeping the board at 100  deg C. This makes the final reflow with the hot air happen very quickly. But really, just the iron and the hot air is more than enough.


73, Bernie


2016 - GM4WZG


Comment Box is loading comments...