SDRTrunk Issues decoding P25 simulcast

[OH-SIGINT]

We are trying to receive the Columbus Simulcast portion of the Ohio MARCS-IP System and are continually running into reception and/or decoding errors.

We've tried every configuration tweak we -- adjusting gain, rate, etc. but to no success.

Here's our current config:
- v0.5.0-alpha6
- 6x R820T Dongles
- Playlist channel configs for each control channel
- Sample Rate 2.880
- Gain 495

 

[AJAT]

Did you try clicking LSM on the playlist editor?

 

[rlmurray56]

Your "gain" setting is maxed out, anything over 40 usually just raises the noise floor. I have mine set at 39 and monitor a simulcast system with very few issues. Not saying that's the answer but it works here.

 

[dave3825]

The frequencies span 9.825 MHz for that site. 6 dongles at 2.4 covers 14.4 MHz and 6 dongles at 2.88 covers 17.28 MHz What other sample rates have you tried? When trying to decode, what is your ppm showing in the tuners tab?

These are simulcast systems that I listen to and I have one config for each system with cc and alts and it works good. I set the frequency rotation delay to 950 ms.

 

[OH-SIGINT]

What other sample rates have you tried? When trying to decode, what is your ppm showing in the tuners tab?

Literally every sample rate. PPM with other non-Columbus Simulcast MARCS sites, which we can clearly decode without issues, is usually around -0.3 or so when on auto correction

 

[OH-SIGINT]

Alright, I seem to have it working again after discovering an antenna issue

Anybody have suggestions to optimize settings for the site?

 

[AM909]

I haven't found anything higher than 2.4 MSPS to be reliable on the RTL-SDR.com v2 or NooElec TCXO dongle, and usually use 2.048 to make the spurs/images noticeably off-channel to help identify them as such (I think). USB cable/hub/port performance may be a factor (SDR# hangs on shutdown much of the time, and sometimes fails to tune the dongle when I try to change freq).

No improvement in S/N beyond about 30 dB RF gain on the the RTL-SDR.com dongle (set to 29.7 normally) and maybe a few dB higher on the NooElec. Anything higher than those produces a bunch of spurs with no better S/N. I'm in a "medium-strong" RF area with a major comm site a few miles away (and 4000' up) and no strong sources nearby. I'm using a CATV amplified splitter with a poor indoor antenna. An outside antenna with different amp/splitter/filtering/cable may require even less RF gain on the dongles.