[Discuss-gnuradio] Problems of lost of BINS

[Milo Wong]

Hi folks,

I have implemented a multi sub-carriers AM transmitter and here I still 
have a strange problem: I plotted the FFT of the modulated signal at 
baseband (as attached) and the number of the bins (spikes) I have on the 
plot was exactly the same as the number of the sub-carriers as I set in 
the program. This is correct so far as I know. But after the signal was 
tuned to 2.45GHz by USRP, the number of the bins(spikes) on my spectrum 
analyzer was not the same, which is only 4 or 6. While I have 20 
sub-carriers at different frequencies and it seems that I lost most of 
them after the signal was tuned to RF. Is there anybody who knows the 
reason behind that? I have been stuck at here for a long time. Any helps 
or suggestions will be greatly appreciated.

Thanks,

Milo