After running my USRP2 with the GRC software I got some results that I didn't expect. My configuration was is simple as an USRP2 source followed by a FFT sink to see the spectrum (around MHz with a 75cm antenna), but:
1) I can only see the sprectrum up to 100MHz. I thought that the LTC2284 ADC had a dynamic range of 575MHz....Why can I only see the spectrum lower than 100 MHz? (When I say that I can not see the spectrum I mean that at 100MHz I get a mirror of the spectrum between 0-100MHz).
2)The spectrum I can see is much more clear around 98MHz, where I can see a lot of carriers corresponding to FM radio stations that I cannot see for instance around 90Mhz.
3) What is the minimum decimation I can set in the USRP2 block? Experimentally I saw it is 5 but I don't understand why.
My specific configuration of GRC is: USRP Source block: Decimation=5, Frequency=(tunable to cover FM band) FFT sink: sample rate=21MHz (105M/5), fft size: 512
In fact when I run my FM receiver (also made in GRC), I can only listen to 89MHz and 108MHz radio stations. I expected to receive the whole FM spectrum.
If some of you have a answers to my questions I will be very glad because I want to understand USRP2 and GNU Radio as soon as possible to became an active member of this community!