Re: [Discuss-gnuradio] Synthesizable Frequencies for WBX?

[Jason Abele]

Yahia Tachwali,

If you send me your actual .grc or .py file, it will be easier to help
you, because I think you may have different sample rates set on
different blocks.

Also, are you cabling TX directly into RX?

Do you have any screen shots of the good and bad scenarios?

Jason


On Fri, Apr 08, 2011 at 07:28:05PM +0000, Tachwali, Yahia wrote:
> Hello Jason,
> 
> Thank you for the instant reply. Here are the responses to your question:
> 
> The transceiver set-up is really basic:
> 
> TX
> ----
> 
> Random src --> DQPSK MOD --> Pulse Shape --> UHD SINK
> 
> RX
> ----
> UHD SOURCE --> FFT block
> 
> so,
> 
> Signal amplitude? 1
> Gain setting? 0dB at TX and RX sides
> Antenna port? TX: TX/RX  RX: RX2
> 
> I believe it is a mis-sampling mismatch. I am using 4 samples per symbol. I 
> should add that this problem appears to be ONLY at the TX side. I am able to 
> see a clean signal when the TX is at 900MHz and RX is 900.050MHz. But not the 
> other way around. 
> 
> Also, as far as the parameters go: if I want to access 900.05MHz I pass to  
> tune_request_t : 
> target frequency = 900M
> LO freq = 50K
> 
> However, the result is: bad signal (i can see the peak at the center 
> frequency expected (900.05MHz) but the bandwidth is wide in the same manner 
> as if I set the center frequency manually at 900.05 rather than using  
> tune_request_t. 
> 
> I am pretty sure that the upsampling in FPGA is messed up or the upconversion 
> setting in the transmitter has to be done in different way.  Any advice 
> please?
> 
> Kind regards,
> Yahia Tachwali
> ________________________________________
> From: Jason Abele address@hidden
> Sent: Friday, April 08, 2011 12:45 PM
> To: Tachwali, Yahia
> Cc: address@hidden
> Subject: Re: [Discuss-gnuradio] Synthesizable Frequencies for WBX?
> 
> On Fri, Apr 8, 2011 at 10:22 AM, Tachwali, Yahia <address@hidden> wrote:
> > Hello Guys,
> >
> > I am experiencing some problems in transmitting/receiving at frequencies
> > around 900MHz for WBX board. While, I am able to do so cleanly at
> > 900MHz, other center frequencies are not.
> >
> > The signal bandwidth : 50 KHz
> > The sampling frequency: 200 KHz
> 
> What signal amplitude?
> What gain setting?
> Which antenna port?
> 
> >
> > I have tried 901MHz , 900.1MHz, 910MHz and many others but the received
> > signal appears to be wider than it should be. The signal level is higher 
> > than
> > -40dbm over the total 200 KHz range when these frequencies are used.
> 
> This usually indicates a sample rate mismatch in your flowgraph, if
> you post an example to replicate your problem, it will be easier to
> help you.
> 
> >
> > The only frequencies I was able to use with no problems are 900MHz,
> > 1.8 GHz , 890MHz, 880MHz.
> >
> > What could be the problem? I have tried to use "tune_request_t" in the 
> > target
> > frequency paramter but it gave similar bad results . Any pointers?
> 
> What parameters did you give to the tune_request_t?
> 
> Have you looked at the tune_result_t returned by set_center_freq?
> 
> Jason