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How to Decode Digital Modes Reliably

Posted: Sun Jan 01, 2017 9:42 am
by MarkHirst
I used my RSP2 Pro in anger for the first time yesterday to receive and record a digital modes broadcast consisting of MFSK32 text, images and Olivia modes.

The result from the human ear perspective was good although with periodic audio stutters.

For computer decoding however, the recording was almost completely useless with extremely high error rates.

I tried changing the speed of the recording to compensate for slanted images, but realised that the degree of slant was continually changing so there wasn't a consistent way to fix the audio.

I'm wondering how I can resolve this. The host PC CPU was running at around 30-40% (although not a fast processor admittedly), does it need a lot more horsepower ?

By comparison, a later recording I made from my computer's line out using a web SDR has come out with excellent images - with all the latency and uncertainty of an internet connection, I'm wondering why that worked better.


Re: How to Decode Digital Modes Reliably

Posted: Sun Jan 01, 2017 5:00 pm
by MarkHirst
Some additional information.

I set up my own short range experiment using a dummy load, and tried different different decimation values.

Images were largely upright except decimation 1 which had some very odd distortions. 2 looked pretty close, but 4 and 8 had some odd slants.

Of course there was no noise at all so any extra CPU work load coping with noise reduction wasn't part of the test.

HDSDR images were fine and undistorted, although noise affected them quality wise - I was just using default settings as the interface is rather more arcane.