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

[Tachwali, Yahia]

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