Hello, I have build an PMR446 Receiver in GNU Radio Companion. I can detect the channel and also demodulate it, but the quality of the receiver is not that much good. I want to amplify my received signal, Anyone have suggestion how to do it. Best Regards, SAJJAD SAFDAR MSc Communication Engineering
on 2012-12-20 18:54
on 2012-12-20 19:25
On 12/20/2012 12:52 PM, Sajjad Safdar wrote: > MSc Communication Engineering > > > _______________________________________________ > Discuss-gnuradio mailing list > Discussemail@example.com > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio You don't say what type of USRP you're using -- is a sample rate of 256k supported on your USRP of choice? Also, your RF is set to 0, perhaps increase this some and see if things improve?
on 2012-12-20 22:59
On 20/12/12 17:52, Sajjad Safdar wrote: > I have build an PMR446 Receiver in GNU Radio Companion. I can detect the > channel and also demodulate it, but the quality of the receiver is not > that much good. I want to amplify my received signal, Anyone have > suggestion how to do it. If I read your flowgraph correctly. Your sample rates are not aligned You have 256k coming out of your USRP [See Martin's reply on this] You then decimate that by 5, which gives 51.2k, but your NBFM receive is expecting 44k1. You then feed that 44k1 out to a standard squelch that is expecting to be fed at 32k, which you then send onto an audio sink expecting 44k1, and a EX GUI FFT sink expecting 256k And as Martin mentioned, you have 0 db Gain. Increase that to 20 or 25 for testing. I'm actually surprised that it managed to detect and demodulate anything with those values, although your basic flowgraph is fine. Do you not get lots of underflows and overflows, as well as a slowly updating FFT ? If it were me, I'd grab 250k of B/W off the USRP, Use a LPF instead of a BPF, Decimate by 5 (to 50k), then use a rational resampler to get to 44k1 (or just get the rational resampler to go from 250k to 44k1), then do the NBFM receive Note NBFM receive block can do *some* resampling, but it has to have the quadrature rate divisible by the audio rate (eg 88k2 and 44k1 are fine, but 44k1 and 250k are not), so you might want a rational resampler block that will do just about any two B/Ws, although takes more CPU Iain