# Understanding the limitations of USRP1

**URL:** <https://www.ruby-forum.com/t/understanding-the-limitations-of-usrp1/234169>\
**Category:** GNU Radio\
**Created:** [February 12, 2015, 12:17am UTC](https://www.ruby-forum.com/t/understanding-the-limitations-of-usrp1/234169 "2015-02-12T00:17:06Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [February 12, 2015, 12:17am UTC](https://www.ruby-forum.com/t/understanding-the-limitations-of-usrp1/234169/1 "2015-02-12T00:17:06Z")

</div>

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

---

<div class="post-metadata">

**Author:** ![tommyjmu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tommyjmu](https://www.ruby-forum.com/u/tommyjmu)\
**Post date:** [February 12, 2015, 1:26am UTC](https://www.ruby-forum.com/t/understanding-the-limitations-of-usrp1/234169/2 "2015-02-12T01:26:34Z")

</div>

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
> 
> * * *
> 
> Discuss-gnuradio mailing list  
> [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
> [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)  
> 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.

---

<div class="post-metadata">

**Author:** ![tommyjmu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tommyjmu](https://www.ruby-forum.com/u/tommyjmu)\
**Post date:** [February 12, 2015, 8:37am UTC](https://www.ruby-forum.com/t/understanding-the-limitations-of-usrp1/234169/3 "2015-02-12T08:37:13Z")

</div>

Aliasing on purpose?

---

<div class="post-metadata">

**Author:** ![tommyjmu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tommyjmu](https://www.ruby-forum.com/u/tommyjmu)\
**Post date:** [February 12, 2015, 9:06am UTC](https://www.ruby-forum.com/t/understanding-the-limitations-of-usrp1/234169/4 "2015-02-12T09:06:27Z")

</div>

> Aliasing on purpose?

Yes, it’s called “bandpass sampling”.

Cheers,

Sylvain

---

<div class="post-metadata">

**Author:** ![tommyjmu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tommyjmu](https://www.ruby-forum.com/u/tommyjmu)\
**Post date:** [February 12, 2015, 10:11am UTC](https://www.ruby-forum.com/t/understanding-the-limitations-of-usrp1/234169/5 "2015-02-12T10:11:08Z")

</div>

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