[Discuss-gnuradio] Flummoxed!

[liverpudd]

Working on  the GNURADIO gr-rds to try and find out why it appears to be finicky with what source drives it.

 

Set up three sources. USRP1, RTL Dongle(NooElec Blue with 0.5ppm TXCO ) and the HackRF.

 

Plugged a decent antenna and tuned to R2 (88.3MHz) a nice strong signal. Whilst the radio works OK with all three sources, the RDS decoding would  only work with the RTL Dongle.

 

Checked the input IQ level from the RTL dongle and adjusted the input level to be the same from the USRP1 and the HackRF. No joy – no change with either the USRP or HackRF decoding the RDS!

 

Adjusted the Rx frequency 88.3MHz +/- 200KHz. The RDS decoder packed in beyond +/- 100KHz on the RTL dongle. No joy with either the USRP or HackRF, no matter what frequency offset I dialled in.

 

Next adjusted the 1Msps sample rate using a Polyphase Arbitrary Respampler.  Adjusted it from 1Msps to +/- 50Ksps in small increments. RTL dongle packed in the RDS decode a few Ksps either side of the nominal centre of 1Msps. No joy from the USRP or HackRF no matter what sample rate I set it to!!!

 

Grasping at straws now, I put a phase rotator in line (can’t say I know what exactly this block does!) but in any case I adjusted the phase by +/- 5 degs. The RTL dongle packed in the RDS decode at about +/- 0.2 degs. No joy with the USRP or HackRF, no matter what phase value I set it to!!!

 

So current situation is I do not know what is going on. I have adjusted all that I can to no avail. Any ideas?

 

Alistair