27 January 2013

PSKmail with the KX3

I've been dabbling with PSKmail over the past few weeks, using my KX3 and a variety of antennas, operating on 10.148MHz as G0HWW-5.

The new jPSKmail client 2.0.x has an embedded modem, but I like to run fldigi in waterfall only mode too, as I get better awareness of what is going on around the PSKmail frequency and how the rigs filters are set up.  I'm also using Xastir to plot stations heard.

So far I've managed to add mail records to 4 servers, DL4OAH-8, SM0RWO, OE5RTL and DL9YCS-3.

This map shows the PSKmail servers that I've connected to and configured my mail settings with.

I've been using an indoor Alex Loop Walkham mag loop and more recently an indoor NORCAL doublet, with the KX3 running at a massive 8W.

This map shows all/most/some of the PSKmail server's and clients that have gated my beacons to the APRS-IS, and of course PA0R, Rein's last reported position.

26 January 2013

Strange filter artifact in KX3

I've just discovered a strange filter artifact in my KX3's filtering.  Whilst fiddling with freedv, and adjusting the PBT high cut frequency with the rig in LSB mode (not DATA-A), as I adjust the PBT-II function downwards, a notch appears at 1500Hz, as soon as FL2 activates.  I have the optional roofing filters fitted, as shipped from Waters and Stanton, and have performed no calibrations myself, yet.

Just to prove that its no artifact of freedv, the same effect can be seen in fldigi.

Has anyone noticed this?

Update: Yes they have. It is explained here.

25 January 2013

FreeDV with pulse audio

I downloaded  the source for freedv yesterday and built it without issues on Ubuntu 12.10 x86_64.  It took a little while to get the sound cards configured to my liking; I wanted both radio I/O and headset I/O to use the pulse audio device, so that I could continue to run fldigi from the with radio whilst running freedv.

There were two minor issues I had to overcome to get this configuration as I wanted.  The first was that I couldn't configure both ins and both outs to use the pulse device, as freedv insisted that the same device couldn't be used for both the radio and headset connections.  I worked around this by choosing the default device for the headset in and out, and the pulse device for the radio in and out.

Two issues remain. The first is that I have to reassign all ins and outs in pavucontrol when i restart freedv, as pulse isn't able to distinguish between the radio and headset streams.

The final issue is that I have yet to find someone to talk to on air.  I'll be using my KX3 at, I guess, 5W power.

There's a QSO Finder for FreeDV here.

2 January 2013

Cheap and nasty USB Soundcards for SDR work

This post is a work in progress.

This pic is the spectrum of the Griffin iMic with no input source connected.

This pic has a stereo pair from the  KX3's I/Q output connected to the Griffin iMic, but with no antenna connected to the radio. The iMic is in line input mode.
In this pic the iMic is in Mic input mode.
Note that in the latter two scenarios with the receiver connected to the soundcard, I'm using a cheap stereo line isolator to ensure there are no ground loops, as I also have a serial connection between the laptop and the radio which gave major problems without the isolation in the I/Q path.


So, I've received the Behringer UCA202 I ordered the other day.  This gave very poor image rejection when immediately hooked up to my KX3's I/Q output.  After some dabbling in gnuradio-cmpanion (grc), I used the UCA202 line output to feed a complex signal into its line input with a 5kHz tone.  I'm only getting about 35dB image rejection when asking the UCA202 to eat its own dog food.
The image rejection gets worse, as expected, when the I and Q signals are independently disconnected or swapped.  This confirms that the signals are wired correctly. In the screen shot above, the peak hold value shows the image peak with only one of the I/Q pair connected.

Some comparitive tests between the Griffin iMic (white model) and the Behringer UCA202, whereby both are forced to consume their own dog food.

The  first test uses a loopback cable to feed the line in from the line out.  No signal is sent to the line out of the soundcard.

Here is the Griffin iMic
and here is the UCA202
Now for test 2. In this test, a 5kHz sinewave at (-20dB full scale) is fed as a complex I/Q signal into the soundcard's line output, via the loopback cable and into its line input.

Here's the Griffin iMic (white)
 and here is the UCA202.