Understanding the limitations of USRP1

GNU Radio
1

I am using a USRP1, and I’m trying to receive FM radio. I’m using a
BasicRX
daughterboard with a 0-250MHz range. The USRP itself has a LO frequency
of
64MHz. Does this limit my frequency range to 0-32MHz, or can I get into
the
100MHz range by somehow multiplying that Local Oscillator frequency?

I get the following error:

– Opening a USRP1 device…
– Using FPGA clock rate of 64.000000MHz…
– Tune Request: 102.900000 MHz
– The RF LO does not support the requested frequency:
– Requested LO Frequency: 102.900000 MHz
– RF LO Result: 0.000000 MHz
– Attempted to use the DSP to reach the requested frequency:
– Desired DSP Frequency: -102.900000 MHz
– DSP Result: 25.100000 MHz
– Successfully tuned to -25.100000 MHz

2

On 02/11/2015 06:15 PM, Tommy T. wrote:

– Tune Request: 102.900000 MHz
Sincerely,
Tommy James Tracy II
Ph.D Candidate
Computer Engineering
University of Virginia

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You might be better off getting a TVRX2 card for it.

You’re limited on the USRP1 to 64Msps, and since the BASIC_RX does no
downconversion–it’s just an ADC “buffer”, you’d be limited to <= 32MHz
in the
first Nyquist zone.

You could put a very stiff FM-band-only filter and some gain in front
of the BASIC_RX, and calculate the appropriate “Nyquist folding” for
your desired
frequencies, and tune to those frequencies in the DC-32Mhz region.

3

Aliasing on purpose?

4

Aliasing on purpose?

Yes, it’s called “bandpass sampling”.

Cheers,

Sylvain

5

On 02/12/2015 09:04 AM, Sylvain M. wrote:

Aliasing on purpose?

Yes, it’s called “bandpass sampling”.

…and it’s a common technique. You can easily demod FM radio this way,
even without a filter (although it’ll be pretty noisy) and I’ve seen
people demod DVB-T this way (probably with filters, though), which is in
one of the higher-order Nyquist zones.

M