Monday, December 31, 2012

Real time Morse decoder - New Ideas

Below is a link to a video clip from CQ WW WPX ham radio contest. I am using CW Skimmer software to decode 100+ stations in this 24 KHz section of the 7 Mhz radio band.

On the left panel the waterfall display shows about the frequency spectrum on vertical axis - horizontal axis is real time.   Blue color is the background noise level,  yellow / orange shows the received Morse code signals. There is also quite a lot of  noise and interference as shown by yellow/green dots.

On the right panel the Morse decoder attempts to decode the signals in raw text mode. There is some 100+ decoder instances active on this demo video. Noise seems to generate a lot of "false" decodes - visible as lines with many "E" or "I" characters.  In Morse code  a single "dit"  is  letter "E"  so it is quite difficult to determine whether noise spike was a real signal or not.  It seems that CW Skimmer software handles this problem at higher level of the decoder chain with Bayesian algorithms.   You can see how the software corrects decoded characters once additional data becomes available.


As I was studying alternative and new ways to tackle the Morse decoding problem from noisy signals I stumbled across this sparse distributed models of sequence memory - see video recognition example by Dr. Rod Rinkus.

I wonder if  this technology could be used for Morse code recognition in noisy HF bands?  Sequence memory would probably help with random "dits"  problem explained above. Once the system learns typical Morse character sequences,  words and phrases that are used in ham radio communications it should be able to recognize real signals from noise.

The system Dr. Rinkus has developed has many advantages such as:

  • Can learn sequences with a single trial 
  • Use Sparse Distributed Representation for individual sequence items and sequences 
  • Can recall individual sequences as well as recognize novel sequences 
  • Constant  computational time complexity -  O(1)  sequence comparison,  O(1)  learning - may lend well in real time processing? 
  • Recognition of noisy and time-warped sequences  

There is a video in  here where  Dr. Rinkus explains in detail how the system works. See also this paper.

Mauri  AG1LE

Tuesday, December 25, 2012

Simple Elecraft KX3 and PowerSDR configuration

I have played with HDSDR and Elecraft KX3 for a while.  While  HDSDR is an excellent piece of software I am more familiar with PowerSDR as I have used it over 2 years.  I wanted to see how KX3  would work with my Flex3000 / PowerSDR  setup.  This turned out to be a fairly simple configuration - in fact you can run multiple instances of PowerSDR connected to different radios simultaneously.  Note that I am using PowerSDR version v2.4.4 on Windows 7.

The first step was to connect the Elecraft KX3  RX I/Q  interface to a sound card in the computer.  A quick visit to Radio Shack was required as I did not have a 2.5 mm to 3.5 mm stereo Y-adapter (part 274-945).  Using a normal male-to-male  3.5 stereo audio cord I connected KX3 to my home brew computer  Line Interface  (Light Blue connector in ASUS P8Z68-V PRO/GEN3 motherboard as shown in the ASUS P8Z68 Manual ).  See fig 1. below  - don't use the pink microphone input jack.

Fig 1.  ASUS P8Z68-V  audio connectors

Next step was to configure PowerSDR  properly.   When you start PowerSDR  without turning Flex3000 on first it will pop up a window - note the button "Add Legacy Radios" below.

Fig 2. PowerSDR Radio Interfaces

You can add SoftRock 40 legacy radio - no need to add anything on Serial Number field.

Fig 3.  Adding Legacy Radios

You will get back to Fig 2. window  and select  "Use" button on the right. Main window of PowerSDR software should come up.  

Next step is to select  Setup menu from the top and General / Hardware Config.  You can setup the Center Frequency here - see Fig 4. below.

Fig 4.   Set Center Frequency

Next you configure the Audio / Primary settings.  In my case I am using the built-in sound card of the ASUS motherboard which is not on the supported sound cards list. There I selected "Unsupported Card" as shown in Fig 5. below.  Also,  I configured Sample Rate to 192,000 to get maximum frequency coverage from KX3  RX I/Q signals.  I also used "MME" Driver of Windows 7  and selected Input  and Mixer to "Line In High Definition Audio"   and selected Output to my video monitor "EQ276W DP-1 (NVIDIA...)".
Fig 5. Audio Hardware Configuration
Time to  press the "Start" button on  PowerSDR.  You should see some signals on panadapter if evrrything is configured correctly. 

Fig 6.  PowerSDR showing 96 Khz of signal coming from Elecraft KX3

Note that PowerSDR expects the center frequency be at 14.200 MHz   (see Fig 4. above) and
to get the frequency display correct you need to tune KX3  at that frequency.   You can also see that PowerSDR covers approximately  96 kHz  bandwidth centered around 14.2 MHz.  Of course you can change that by just going to Setup menu.  

Fig 7. Elecraft KX3  tuned at 14.200 Mhz

I was running Flex3000 and KX3   in parallel listening some stations while switching the antenna between KX3 and Flex3000.   I did not do any scientific A/B comparison study  but just by  using two instances of the same PowerSDR version connected to different radios I could not really tell much difference between these two radios.  Both picked up the faint  DX stations equally well.  The only difference was really the few kHz noise band around the KX3 center frequency  - outside of that the sensitivity and sound quality was very similar in both of these radios. 

I was also playing with the CAT interface of PowerSDR  - however, it does not recognize Elecraft as an option so I did not spend much time on that.  In comparison HDSDR uses Omnirig  CAT interface which has more choices, including Elecraft K3  that works well with KX3.    If you can figure out a way to get KX3  CAT interface working also with PowerSDR please let me know.

In conclusion I wanted to test if I can make PowerSDR software to use Elecraft KX3  as a receiver.  As you can see above this was a quick and painless configuration effort.

Mauri   AG1LE

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