FMP24 vs SDR#

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Eric61

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I'm using DSD+ Fastlane v2.39 and FMP24 v2.19 to trunk-track a 4 frequency Cap+ system. Voice channel tuning/reception is with a NooElec SDR dongle. Everything works great with one exception; I don't get very good voice decode- probably about 80%. However, if I park SDR# on one of the same voice channels and route the signal to DSD+ through VB Audio cable, voice decode is near 100%. I have tried adjusting gain and bandwidth in FMP24 with no improvement. Also tried minimizing FMP24 (as was suggested in another post) with no change, but I doubt CPU processing power is the issue.

Since the dongle is tuning the voice channel in both instances, shouldn't the decode ability/rate be the same? The only other factor is the use of a scanner to monitor the control channel and tell FMP24 the frequency to tune, but once tuned, shouldn't the voice decode be comparible to using SDR sharp to feed DSDplus?

I have also performed fine tuning of DSD+ and found the defaults give the best decode rate. At this point I'm not sure what else to try and am open to any suggestions.

Thanks,

Eric
 

Eric61

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CORRECTION
This is a Connect Plus system rather than a Capacity Plus system as originally indicated although I don't believe this changes anything relative to my question.

Eric
 

mtindor

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Is there any chance that you don't have FMP24 set up to adjust for the drift of the dongle [if there is any neglible drift]? In SDR#, you almost certainly would since it's easy to see when you are off freq and the controls are right there.

I'm asking because i'm thinking that perhaps FMP24 is actually tuning off freq. EVen if you have something directing the dongle to tune to 464.3875, for instance, if FMP24 isn't set up to account for the proper drift, you might actually be tuning to 464.37 or something like that. Of course, I thought FMP24 will autotune if it's close to a sig.

Still, make sure you have adjusted for any drift if you don't have one of those < 1 ppm TCXO dongles. The dongles that are very old [at this point] have a lot of drift that needs to be accounted for.

Otherwise, I would not think that FMP24 would do worse on a dongle than SDR#. They should provide pretty much the same. Of course, if you are using a dongle in SDR# and have it set to some really low sample rate, it's going to be more immune to overload, whereas FPM24 is going to actual use the 2.4 msps or whatever sample rate and thus could suffer from more overload.

Mike
 

Eric61

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According to the zoomed spectrum display in FMP24, tuning is spot on and the dongle is supposed to be stable to within 1ppm. SDR# is using 2.4 MSPS- same as FMP24.
 

mtindor

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According to the zoomed spectrum display in FMP24, tuning is spot on and the dongle is supposed to be stable to within 1ppm. SDR# is using 2.4 MSPS- same as FMP24.
I don't have an answer for you then. My FMP24 has always worked better than piping data out of SDR#, assuming I have the proper filter selected.

Mike
 

M105

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One thought that comes to mind is the bandwidth setting in FMP24. Does it match what you are using in SDR#?
 

Eric61

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Bandwidth in SDR# is 12.5 kHz. Bandwidth in FMP24 is auto-selected at 7.6. The latest version was supposed to have enabled the bandwidth locking command line option (using -b<bw>), but it doesn't work. Changing the bandwidth in SDR# to 7.6 to match FMP24 doesn't degrade decoding.
 
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