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

From: Hongliang Zhang
Subject: Re: [Discuss-gnuradio] Problem of using UHD blocks as Tx & Rx
Date: Thu, 28 Oct 2010 07:22:59 -0700 (PDT)

Dear Marcus Leech,

Thanks very much for your response.

I use RFX2400 daughterboards and their TX/RX ports.

A attenuator is added between the transmitter and receiver boards now. And
to simplify the test, I use a constant source at the transmitter side.

Here is my GRC flow graph:


And here are the results I've observed from the scope:


Why do I receive a sine wave when I transmit a constant?

Best wishes,

Marcus D. Leech wrote:
> 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
> problems.
> 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
> http://www.sbrac.org
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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