DSD Troubleshooting

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bcradio

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Hi Folks!

Wondering if you could help me out. I've been having problems getting a decent decode with DSD, with both versions 1.2 and 1.3. I'm trying to monitor my local Smartzone digital voice traffic. It's unencrypted C4FM, and my best decode rates are about 4-5%, mostly choppy and garbled audio.

I've tried different input settings, and sliding the signal input up and down but the best I can do is 4-5%. Running Ubuntu 10.04 on a Pentium 4 3.2 gigahertz processor, 1 gig of ram.

The soundcard is a Soundblaster Live 24bit card.. I've tried using both that and the onboard internal sound card, but have no improvement using either.

One thing I'm wondering is that my discriminator tap is not up to snuff. It works just fine for Unitrunker/Trunker/Trunk88 etc., but maybe isn't good enough for realtime decoding of digital voice?

I've attached a screenshot of DSD in action, perhaps there is a clue in it?

Any suggestions?

Thanks in advance.
 

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MattSR

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This is most lively down to an audio level problem - the fact that it works perfectly with 2FSK (Unitrunker/Trunker/Trunk88 - which are all 2 level FSK) and it then falls over with ASTRO/P25 voice tells me that its an impedance mismatch or level problem.

As Rick has previously mentioned, perhaps an buffer (unity gain) amplifier inline might help..
 

SCPD

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Here we go again :)

Run a software oscilloscope to see the waveform. Adjust signal level as needed.
 

bcradio

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I guess I assumed that the waveform was good because it worked so well with the trunker programs. I'll check out and find a linux oscilloscope and give it a whirl.
 
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