Hi folks!
I don't no if this is the right way to request help regarding op25.
Let me try :).
I am trying Op25 decoder (scope.py) + USRP. Although I can get the air interface signal, the error rate is too high and the voice signal is rarely intelligible.
The radio I have is setup in direct mode in 800MHz (a bit higher than the ones I saw in previous work).
Using the signal analyzer app (osmocom_fft.py) I can detect the signal with a high power level using the same antennae and gain settings.
I have already run the scope.py (osmocom) and got the audio and radio info. It seems that the scope.py+USRP request a high frequency offset (7.5kHz) to tune the carrier and try to decode the air interface signals.
I have: USRP_N210+WBX+tuned_antenna+Ubuntu+GNURADIO-3.6.5.1+OP25_osmocom.
May the higher frequency request another setup I missed?
Am I missing many details? :)
TIA
There are many variables that could affect this - what version of the programs are you running?
The most common possible causes are 1) the USRP RF/IF gain setting(s) must be tuned for optimum reception. Later versions of scope.py have a --gains [-N] parameter - you can use the osmocom_fft application to adjust the gains to find the best values. 2) there is a frequency offset in all USRP's unless you have a GPSDO - the offset must be accounted for when tuning
3) there is a DC offset (at zero IF) which can be "cured" (circumvented) using the -o option (I usually use -o 50e3) 4) Trying to receive LSM/CQPSK in disctap mode
For more help we'll need to know the versions of op25 and gr, the command line typed, and ideally post screen captures of your spectrum, eye, and constellation plots...
Max
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Jacob Blanks