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Re: [Discuss-gnuradio] Problem of using UHD blocks as Tx & Rx

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Problem of using UHD blocks as Tx & Rx
Date: Wed, 27 Oct 2010 14:32:33 -0400
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On 10/27/2010 02:11 PM, Hongliang Zhang wrote:
> Hi everyone,
> I made a test for UHD blocks today, and I found a problem as follows:
> I take two USRP2 boards for my test. One is used as transmiter and the other
> board is set to be receiver.And I use UHD Simple Sink and UHD Simple Source
> blocks for transmiting and receiving respectively. 
> sampling frequency = 195.312K (which is the minimum sampling frequncy of the
> system). 
> gain=0
> The transmitted signal is a AM modulated sine signal. 
> The frequency of orignal sine wave (the message signal) is 10K Hz.
> The frequency of carrier signal (center frequency for modulation at
> transmitter board) is 2.42 GHz, and I use the same frequency at the receiver
> board for demodulation.
> Amplitude of transmitted signal is 0.05.
> I connect the two boards together, and I add a scope to observe the period
> of the received demodulated signal. The problem is the period is about
> 0.000045, which means the frequency of the signal I received is not 10 KHz,
> but about 2.2 KHz.
> I have used the same external reference clock and PPS signal for both of the
> boards, so I think they are set up correctly. Why do I get a received signal
> with different frequency from what I transmit? 
> Does anyone meet the similar problem before? How may I solve the problem?
> Thanks so much for every help and suggestions in advance.
> Best regards,
> Hongliang
What daughterboards are you using?

Can you share your (GRC) flow-graphs with us--makes it easier to spot

I hope that you're using an attenuator between the transmitter side and
receiver side.

My guess is that there's a sample-rate issue somewhere on the receive
side, like the scope sink
  hasn't been told the correct sample rate, so it's displaying
incorrectly, etc.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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