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Re: [Discuss-gnuradio] Bandpass Sampling

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] Bandpass Sampling
Date: Mon, 08 Dec 2014 21:24:52 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0

There's so much Marcus in here ;) so here's my answer: usually, you'd use the USRP+WBX as direct conversion receiver, not an IF one.

Regarding WBX documentation: have you seen the performance measurements [1], and the UHD manual [2]?

Is there some specific information you're missing?

Best regards,

PS: if you'd agree, I'd like to shift this discussion to address@hidden .

[1] http://files.ettus.com/performance_data/wbx/
[2] http://files.ettus.com/manual/page_dboards.html#dboards_wbx

On 12/08/2014 08:57 PM, Richard Bell wrote:
I think Marcus answered my question. Thank you.

On Mon, Dec 8, 2014 at 11:53 AM, Richard Bell <address@hidden>

I'm apologize. I am using a WBX card.

I forgot to mention that I've been looking for a datasheet for the WBX,
but all I can find is the PCB schematic doc on the ettus website which
isn't very useful. So I don't know what the IF frequency coming out of the
WBX is. Does the WBX tune itself given the UHD source settings so that the
IF it produces is proper for the USRP ADC?


On Mon, Dec 8, 2014 at 11:28 AM, <address@hidden> wrote:

 The N2xx series use a fixed sample rate, so there's no "deciding what
sample rate to use based on Fc".

There's also the analog bandwidth of the ADC to consider.  If you aren't
going to use a downconverter card, then the analog bandwidth of the ADC
will start to roll-off at some point, so even if you narrowband filter your
input signal to remove aliasing possibilities, you will end up in the
roll-off skirts of the analog bandwidth of the ADC.

Is there some reason not to use a downconverter card, like the WBX for
your application?

On 2014-12-08 14:23, Richard Bell wrote:

  I have a binary FSK signal centered at 300 MHz with 160 kHz offset
peaks from the center freak. Therefore the lowest signal frequency of
interest is 300-0.16 = 299.84 MHz and the highest is 300.16 MHz.

I know the maximum sampling rate of the USRPN210 ADC is 100 MSPS. If the
USRP uses that sample rate of 100 MSPS, it will alias my signal onto itself
in an unwanted manor.

My question is, how does the USRPN210 decide what sample rate to set the
ADC to? Is it a function of both the center frequency and the sample rate
setting of the UHD source block?


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