Strange 25MHz peak in spectrum of USRP2 output signal

Dear all,

In a spectrum of USRP2 output signal, I found a peak of which origin is
unclear.
The frequency of the peak is 25 MHz and the peak is always observed.

The attached png images are the results of FFT of USRP2 output signal in
the case that no signal is fed in RF1 port. One is the result by
uhd_fft.py and the other is the result of FFT of waveform data which is
obtained by uhd_rx_cfile.py. The 25MHz peak is observed in both results,
therefore, I think this peak is true.

In addition, there is a peak with the frequency of 50MHz, although I do
not attach the images of FFT to this e-mail.

Please let me know the origin of the 25MHz and 50MHz peaks.
Did I do what was wrong in installation of UHD or use of firmware/fpga
images?

I use UBUNTU 10.10 and USRP2 with a daughter board BasicRX.
I installed Gnuradio and UHD automatically by using the script supplied
by Mr. Leech and use firmware/fpga images in /usr/local/share/uhd/images
folder. In the installation of UHD, I think there had been no error
message.

Best regards,
Nakajo T.

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