On 12/07/2018 06:01 PM, cesar wrote:
Hello
Im new in GNUradio and I am trying to build a spectrum analyzer using
a USRP, to sweep the spectrum from 0 to 112 MHz. In order to scan the
total 112 MHz window, I see individual 8 MHz bandwidth windows at a
time. But I see that at 64 MHz the spectrum repeats.
My question is why the spectrum repeats at 64 MHz? and how can I solve
it?
Somebody can help me please?
The features of the USRP are:
ADC sample rate = 64 MS/s
clock frequency = 64 MHz
daughterboard = BasicRX with range 1-250 MHz
I attach the spectrum of the 0-8 MHz and 64-72 MHz windows to example
the case and my flowgraph in GRC.
This presumably is a USRP1, given the 64Msps sample rate.
The Basic_RX card is just a "buffer" between the RF connectors and the
ADC. While it has 250Mhz of *analog* bandwidth, you're still subject
to Nyquist, which means that everyone above 32Mhz will get aliased,
given the 64Msps ADC.
When using the Basic_RX, particularly as a beginner, it's best to put a
stiff 30Mhz low-pass filter in front of it. Once you're comfortable
with that,
you can investigate "bandpass sampling" or "sampling in the 2nd or
3rd Nyquist Zone".
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