Unexpected peaks in spectral analysis I am doing the spectral analysis of some antenna recorded signals by computing PSD (logarithmic absolute value of the FFT) and the spectrogram of the signal. The problem is that I get some unexpected spikes in the signal that appear through all the signal, as it can be seen in the next figure:



The two peaks that appear are the spikes I am speaking about, and they are the same in all the signal. The center spike is not located in $0\textrm{ Hz}$, so it is not a DC offset of the signal. This is giving me some problems, so I would like to know what can they be or how can they be removed (maybe I am not computing the spectral analysis correctly). 

I have also performed Welch PSD estimations, and the peaks still appear. I have been told that it can be some internal interference form the electronics recording the data or some issue with ADCs.
The large spike at ~9MHz could be some form of interference from electronics near the receiver or internal to the receiver (maybe from using a poorly conditioned power source).  My best guess for the spike at DC is a DC bias from quantization.  If the digitizer truncates instead rounds, the resulting digital signal will have a non-zero mean and therefore a DC offset.  We had this happen in an FPGA downcoverter implementation at a previous job.  Once they changed the FPGA to round, the DC offset went away.  If you have ever used an Ettus USRP radio, you see the same DC offset in many of those boxes.