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

[Hongliang Zhang]

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



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