Tag: data modes

Using an SDR and VAC to Decode Data Modes

Web SDR receivers allow you to remotely monitor the radio spectrum, and phone (voice) is quite easy you just click and listen. You can also use SDR receivers to decode date modes, be that CW, PSK, RTTY, HF-DL or Olivia.

The principle is the same, you need to route the audio out of the SDR, and into your data modes decoder. This requires a virtual audio cable, you will find quite a few both paid and free version on the web. It is “virtual” because you need to connect the audio from one port on your computer to another with software.

Here you will find some free virtual audio cables (untested) or you can try the most popular (but not free) version virtual audio cable program.

So you have now downloaded your VAC, next find an online SDR like this one, or others are available at sdr.hu.

Start up the web SDR and select the frequency and mode that you want to decode. Here you can see we have centered on an Olivia signal, 16/500 on 5 MHz (5366.5)

Now you need to configure the audio IN and OUT. In my case, it looks like this. Note the WAVE IN set to my sound card, and WAVE OUT set to Virtual Audio Cable

You now need to decide what program do you want to use to decode the data. Fldigi is a good free choice, I used DM780 from Ham Radio Delux but you may also want to check out Sorcerer.

HRD also have an old free version, it is worth considering and can be downloaded here.

You will need to tell the data decode program to use the virtual audio cable as the “input” sometimes called “microphone in”

Here is my sound card setting in DM780. Note the INPUT device is shown as “Line 1 Virtual audio cable”

So we now have VAC running, and our software looking for audio on VAC. Now we need to select the mode to be decoded, here is Olivia 16/500

The signal should now decode, the text should be appearing in the box, and you can see the data signal in the window.

Remember you can decode virtually any mode with the correct software.

CQ WW RTTY Contest

CQ WW RTTY is the perfect excuse (if you need one) to turn on the amplifier and have a play with the big boys. Its never been more popular, no longer do you need a separate room for your RTTY teletype printer just a PC and some logging software should be fine.

I have in the past completed most of the 48 Hrs as part of a team, making thousands or “QSO” but this year was a much more relaxed casual event. The plan was to grab a few hrs operating over the weekend, in between the usual tasks.

The linear would allow 400w RTTY with around 5w drive, to the doublet antenna. The doublet is 10m per leg, and fed with 30 Ohm ribbon it doesnt make a very nice match on 20m ! The alternative antenna is a 8m vertical with an auto ATU at the base. The CG5000 is a 800w PEP remote auto ATU, although I dont use the amp with this antenna and choose to run 200w barefoot from the TS990 in this configuration.

Remote ATU near the base of the antenna are hard to beat if you haven’t got a resonant  antenna, helping to reduce large mismatch in the feeder and the subsequent loss of power. One disadvantage is they need to be powered, the CG5000 requires 12v and isn’t equipped with a bias tee. This requires a separate power cable to be run to the bottom of the garden, fine in my postage stamp but maybe an issue if you own 2 acres !

After spending some time on the bands it was obvious 10m was closed, 15 was a little better but as usual the “easy band” 20m was open and provided some of the best contacts. In total I worked 132 Q in 42 DXCC, using SH5 to analyse the log. The program can be used to check and map many of the stations you work, allowing you to gain a great insight into your operating and in some cases multi operating / radio station.




Here you can see a basic list showing DXCC worked. The mast files contain information on and the location of many of the regular DX stations, and so distances and bearing information can be analysed in tabular and graphical format.




RTTY and logging was provided by the excellent N1MM software, as usual its a real credit to Thomas for a massive free contribution to amateur radio.

FSQ on 5 MHz

FSQ is a Fast Simple Qso chat mode, a bit like chatting by SMS or Skype but of course using RF. The FSQCALL protocol was developed by Murray ZL1BPU with significant input from Con ZL2AFP. Murray suggests all the hard work was done by Con 🙂

FSQ is intended for fixed frequency (channelized) operation, with dedicated calling frequencies. It isn’t intended as a ‘tune around to see what you can find’ mode!

Suggested Frequencies

Region 1 (Africa, Europe , Middle East)
80m 3588 kHz USB (sunset to sunrise)
60m *5367.5 kHz USB local day
40m 7044 kHz USB (sunrise to sunset)
30m 10144 kHz USB (local day, DX night)

*suggested UK freq for 5 MHz.

Region 2 (North and South America)
80m 3594 kHz USB (sunset to sunrise)
40m 7104 kHz USB (sunrise to sunset)
30m 10144 kHz USB (local day, DX night)

Region 3 (Australia and Asia)
80m 3580 kHz USB (sunset to sunrise)
40m 7105 kHz USB (sunrise to sunset)
30m 10149 kHz USB (local day, DX night)

You can read more about FSQ and the way it can generate automatic replies from station monitoring the frequency. You will need to understand how the commands work.

To help you get started have a read at the operating guidelines published here. They establish some rules around callsign format being in lower case and what frequencies to try. One option for inter G is to try 5 MHz, put your dial freq on 5367.5 USB and call CQ.

You can download the software on ZL1BPU website, for some reason we have a USA and rest of the world version. I would suggest you select the rest of the world version (unless your in the USA) as for some strange reason they dont both centre the signal as 1500 Hz (centre of the waterfall) if you try and use the USA version and the other station have the rest of the world version you cant operate on the same dial freq.

FSQ was developed by Con Wassilieff ZL2AFP with the assistance of Murray Greenman ZL1BPU. The first QSO took place between these two on 28th November 2014, and the first Alpha executable release was on 17th December 2014. The source code was released with the Beta version 0.23 on 3rd March 2015. The first US version release (V0.24 RC1 by Bob NW8L) was on 29th March 2015. The first full-package public release was by Bob NW8L on 29 April 2015.

A version of fldigi with full FSQ support was released by Dave W1HKJ on 16 July 2015, and includes support for Linux and Mac platforms.

More information on FSQ and fldigi is available online.

The software requires very little setup, just add your callsign (lower case) and locator. You may need to use VOX to key the radio, much depends on your local setup.

Here you can see a screen grab from a chat with G4VLC Peter, G0VPJ John, G4DAX Dave on 5367.5 MHz USB



73 Dave M0TAZ


Data Modes for all Occasions

I recently completed a talk at LEFARS on data modes for all occasions, the aim of the talk was to explore alternative data modes. We have all received the very popular PSK, most likely on 14.070 but many other data modes exist some offering much greater reliability and alternative uses.

The slides will hopefully get you thinking about other data modes and some of their advantages and disadvantages, how to identify them  and what programs to try.

One such free program HRD can be found online, although if you want support for modern radios and bug fixes why not use the try before you buy option on the paid HRD website.

You can download the slides data modes for all occasions.pptx (1)

73 Dave M0TAZ

© 2015 Dave, M0TAZ