Human Planet

Ham radio PC interface

Hi all,
As promised in my last post, I have finally finished designing and building a cheap interface to connect ham radios or any other audio device that does not share audio common ground to a PC, including a PTT interface. Price should be around $17 or 60 NIS.  The control is done using a USB interface, so unlike most ham radio hardware that uses serial connections, this one is plug and play in modern PCs. The neat thing is that it uses them same commands as a RigBlaster. So this interface works out of the box with common ham radio programs like Echolink and Svxlink. The interface should also work with soundmodem which can be used for X.25 packet digital communications, without any extra hardware (I am still trying to get this to work). This interface could also be used to connect to other devices that don’t share a common ground. For example like phone lines.

Parts you will need

1. TTL USB Serial interface – The main part is a simple CP2102 $4 controller that can be percussed from ebay. It simulates a serial device, meaning you can still work with older pieces of software with it. Note though you need to solder a cable from the RTS pin on the board, because normally they don’t come with a pre-made pin.
2. Audio line isolation transformer – This can be easily salvaged from any old dial-up modem. That’s how I get mine, it seems to be much easier to get them off old modems than finding them in electronics shops, plus they are so easily identifiable (just make sure not to break the contacts when you take them out, happened to me twice). If you can’t find any old dial-up modems you can get it from ebay.
   
3. 3.5mm stereo and 2.5mm mono earphone connectors – You need one of each, PCs use a 3.5mm stereo jack and the radio’s microphone is usually a mono 2.5mm jack (consult your HT’s manual, they tend to have a schismatic for the mic). I personally like to have two 3.5mm phone plugs on each side and an adapter, so in the future I can use this interface for other things than ham radio.
4. (recommended) Isolated audio cable – Ham radios can produce a lot of interference and using isolated audio cable close to the transformer is a good idea, you won’t need more than half a meter, unless you want to put a larger distance between the radio and the PC.
5. Prototyping Perfboard – So you have what to solder the parts on.
   Now comes the difference between the two circuits, you MUST have either of the two options 6 or 7 below:
6. (option 1) Reed relay – If you manage to find this part number HE722A0510, then you will really get a simple board, with just 3 parts on it. Its also quiet compared to a normal relay.
7. (option 2) 6 pin 5V mechanical relay and two NPN 2N3904 transistors – Adding two more parts to the board and a louder relay, this would be a lesser choice, but still fully functional interface. I am putting this as an option because these parts are so common I doubt anyone would have a problem finding them.
8. (recommended) 14 pin socket – If the relay breaks, it would make it easily replaceable.
9. A 3.5mm audio splitter and a set of cheap earphones – Most sound cards today have a circuit that checks if a device is plugged in to the card, otherwise they would not play anything though it. To overcome this you can split the outgoing audio signal, connect one side to the radio interface, and the other to a set of earphones. This is not needed if you want to plug a device like an MP3 player, where there is no such check.

The Schematics

I am going to supply two schematics, the first is the one I built which uses a reed relay, which is more quiet, faster but slightly less common and costs around $3 more. The second, I built and tested on the breadboard. It uses a normal 8 pin mechanical relay and two NPN 2N3904 bipolar transistors.

The finished interface looks like this:

PTT Interface option 1 using a reed relay and the CP2102 USB to UART controller

And here is the schematic:

PTT Interface1 using a reed relay (click image to enlarge)

Note that the reed relay I used can handle the strange 3.3V to 5V connection used (pin 2 and 6 on the relay). This saves the need for an inverter, since for some reason, the TTL’s logical high is 0V and logical low is 3.3V and not the other way round (still trying to figure out if this is the spec, or the Chinese assemblers fault).

If you can’t find part number HE722A0510, then you could use two NPN 2N3904 transistors and a 8 pin mechanical relay. The NPN transistor on the left inverts the signal, while the transistor on the right amplifies the signal to 5V. This is the schematic:

PTT Interface2 using a normal 8 pin relay (click image to enlarge)

Will build ham radio interfaces for food – If you want I would build you one

I am willing to build these for people  and get paid via paypal, price is negotiable, but I don’t think I’d be willing to build this for under $55 (or 200 NIS). If I find cheaper ways to get parts, I’ll lower the price. This depends on how much call there is, and if I find a cheap way to print PCBs for this project.

I  hope this interface brings use to people.  The one I built I hope to donate to the Jerusalem Amateur Radio Society operations.

Thanks

As usual, I could not have done this alone, thanks to 4Z5UG, Eric, who helped me out with the inverting NPN circuit design, and for 4X1GM for suggesting the reed relay.

That’s it, Looking forwards to hear your thoughts on this post, 4Z7GAI wishing you 73, best regards.

With the dissertation defended I plan on bringing this blog back to life.

I started a post-doc position with the Cornell eRulemaking Initiative (CeRI), based in Cornell Law School. The project runs a very interesting operation called Regulation Room. It offers a platform and, even more importantly, a process for online public participation in the federal government rule-making process (if you don’t know what rule-making is, you are with the majority of people out there and should definitely go to the Regulation Room, because it has all the explanations). I will be working on collaborative drafting of policy input and consensus building around policy issues; aspects that currently are absent from the platform and frankly not sure will be necessarily a standard part of it. I hope to write about this work as I move along.

Yet, even before I started working on my own piece of CeRI research, just learning about the Regulation Room prompted interesting conversations that easily linked to my interest in the digital divide. The result is a paper I co-authored with one of my new colleagues, Rebecca Vernon, which will be presented later this week at the ”New ICTs + New Media = New Democracy? Communications policy and public life in the age of broadband” (CFP) – a workshop organized by the Institute for Information Policy at Penn State University and the New America Foundation.

I am not sure what the policy of the workshop is about publishing the papers, so in the meantime I’ll post the extended abstract. Hope you’ll find the premise interesting. If you are interested in the rest, please email me or just leave a comment.

Between Twitter revolutions and Facebook elections, there is a growing belief that information and communication technologies are changing the way democracy is practiced. But how universal are those effects? In this paper we look into what van Dijk labels “motivational access” in digital divide as an impediment for citizens to actively utilize information and communication technologies for civic engagement. We focus on the Cornell University eRulemaking Initiative as our case and conduct an in-depth investigation into its recent efforts to get the public involved in the Department of Transportation rulemaking process using online tools. Recommendations based on this analysis address both national policy frameworks and agency specific regulations.

The digital divide is viewed as major impediment to information-technology-enhanced democratic processes. But if you build it, will they come? Will making broadband more readily available necessarily increase participation in democratic processes? Will making government information available online motivate citizens to engage with government institutions? Will opening up communication channels necessarily yield productive feedback from people? Are the barriers for meaningful civic participation online primarily technological?

Regulation Room (http://regulationroom.org) is a project of Cornell University eRulemaking Initiative (CeRI). It is an online platform developed to engage the public in the federal agency rulemaking processes. In addition to its technological platform, Regulation Room has developed a set of moderation and outreach techniques to make both the procedures of rulemaking and the content of the rules more accessible to the general public. CeRI works with the Department of Transportation on actual rules the agency is seeking public comment on. As such, it serves as a real-life laboratory to explore uses of technology in democratic processes.

Over the past 15 months, Regulation Room worked on 3 rules that resulted in formal comments submitted to the Department of Transportation. In this paper we unpack what it takes to engage citizens in democratic processes and help them make their participation count. Our analysis suggests that while digital divide defined in terms of physical access and technological literacy may play a role in impeding civic engagement, they may not be the only important factors. In effect, while ensuring that all citizens have broadband access and well-developed technical skills go a long way toward ensuring public participation in democratic governance, it will not result in the desired breadth and depth of participation without further policy changes and investments in new technologies. Practices that evolved around the use of technology on the one hand and the engagement with government processes on the other, play an important role affecting civic online participation.

The paper presents an assortment of lessons and observations from “Regulation Room” and offers policy recommendations that suggest viewing civic online engagement through the lens of socio-technical practice, wherein the technology requirements for citizens to engage effectively in democratic processes are examined in conjunction with the normative assumptions of individuals as they interact with their government through online media.

The Jerusalem Echolink Node (4Z7GAI-R)

Hey all,

I recently got my amateur HAM Radio license from the Israel ministry of communication. My call sign is 4Z7GAI.

I have been working on getting an Echolink node running on the Jerusalem repeater using Linux. Echolink is a closed proprietary software that lets you connect ham radios to one another and key them across the Internet. Luckily someone wrote a FOSS program called Svxlink, which lets you connect to the Echolink network on Linux., A remote radio control with an echolink server, svxlink-server and an Echolink graphical client, Qtel. I am going to explain in this post how to get svxlink compiled and working (compiling is the hard part). I will also giving out here an Ubuntu package for the lazy ones among you.

I will also add a small section on the physical connection to the radio, an old Icom IC-02AT from the 80s (around my age).

Compiling Svxlink For Debian, Ubuntu packaging and Installation

My system is Debian, ubuntu needs a few extra lines and they are supplied in section number 2. If it isn’t, here is a .deb package for Ubuntu.
Note that I am checking out the qt4 branch.

1. sudo apt-get install libqt3-mt-dev libsigc++-1.2-dev tcl-dev libasound2-dev libgsm1-dev libpopt-dev subversion checkinstall
   svn co https://svxlink.svn.sourceforge.net/svnroot/svxlink/branches/qt4 svxlink
   cd svxlink/src
2. Only in Ubuntu (not Debian, these lines are not needed there) type these commands: mkdir -p async/audio/alsa ln -s /usr/include/sys/asoundlib.h async/audio/alsa ln -s /usr/include/gsm.h async/audio/ ln -s /usr/include/popt.h echolib/
3. Then run:make
   sudo checkinstall
4. Then press  2 and type “svxlink” to give the package the right name.You will have a .deb package you can install now with dpkg -i svxlink.deb

Troubleshooting:

If you are getting strange compile errors, don’t panic, its pretty normal for svxlink. Post them here, or search for them in the svxlink message archive. There are quite a few common ones.

Installing the voice files

Svnlink can speak out information on the node, for example callsigns of hams joining in or announce the time. For that you need the freely available sound files from Svxlink.
Download the the heather sound package from the svxlink sound downloads
Extract the contents (including the en_US folder inside) to the path: /usr/share/svxlinks/sounds . You may need to create the sounds folder.

Configuring Svxlink

Svxlink has many options. And detailed man pages of what they all do. The main configuration is in /etc/svxlink/svxlink.conf where you set up your callsign for the station, the RX and TX sound ports and logics. The logics let you decide if you are running a simplex repeater or a full-duplex repeater. Also you can set which modules should be used (including Echolink). Each station is unique so you will need to go over the configuration slowly and figure it out. The svxlink.conf manpage is well documented.

The echolink configuration is located at /etc/svxlink/svxlink.d/ModuleEchoLink.conf . Again, its pretty simple and there is a ModuleEchoLink.conf manpage (if you get stuck on something just comment here).

My custom hardware interface Hardware

The circuit is simply a computer-controls relay switch. Opening and closing the audio connection between the PC sound card output, and radio mic-in.

To interface with the computer, I used my beloved Bumble-b that I posted about before. However the bumble-b is not being made anymore (we don’t know if the maker of the bumble-b, dfletcher, is dead, alive, or neither). I hope to post here later a simpler interface using a $2 usb-serial interface. But for now you can see the general idea: you could use any other computer interface that opens and closes a relay (an LPT port for example), this relay would connect the mic-in of the radio in to the speaker of the computer’s sound card, serving as a Push-To-Talk button.

The radic-mic and PC soundcard are connected to each other via an audio transformer taken off an old modem, as shown in the picture below. You can get these transformers off any old dialup modem, its easy to spot the coil on the modem board too. The transformer goes between the radio and sound card because they don’t have a common ground, if you just plug them together one would fry the other. However the radio’s speaker out and PC’s mic-in are just plugged in directly. That seems to work fine when the sound on the radio is set down low, still, you could use another transformer if you want to, it might give better results for some radios.

Custom PTT Interface for svxlink

Software

For svxlink to key using this custom interface I had to slip a few quick and dirty lines of code in to the files src/svxlink/trx/LocalTx.cpp and src/svxlink/trx/LocalTx.h .

Here is the patch. Its generally useful to look at if you have your own commands to key your custom-built PTT for svxlink. In mine I just echo to /dev/radio ‘y’ and ‘n’ in order to open and close it respectively.

Come to my new Echolink node!

I hope this helps anyone who wants to work with svxlink. You are welcome to come to my echolink node at 4Z7GAI-R that connects to the Jerusalem repeater in Israel (R1).
I connect to it now using the android app for echolink. So I can key my radio from anywhere!

Thanks

Also great thanks to strata who is on the #hamradio channel on freenode, he showed me the program and that its worth doing the painful compiling for it (it was much more painful before this blog post).

Also thanks to Geoffrey Mendelson (4X1GM). Who gave me the radios and antenna to build the repeater, and his help along the way.

Comments are welcome as usual

73 for now