You might also want to check out Jeff Long's presentation on sampling
rate at the GRCon15 Intro Day:
http://www.trondeau.com/grcon15-presentations#monday_Long_Sampling
Video: https://www.youtube.com/watch?v=AmY7fCGTKs4
Tom
On Wed, Sep 16, 2015 at 5:57 AM, Marcus Müller <marcus.muel...@ettus.com
<mailto:marcus.muel...@ettus.com>> wrote:
Hi Gerome,
I hope the subject I've added suits the topic of your mail well; if
not, feel free to change it when replying)! It's kind of important
to have a proper subject line, as it'll allow people to directly
address your mails.
What does the sampling rate in this usrp block does?
It sets the sampling rate of the stream of samples coming from the
USRP.
Is this the one that samples the IF from my TVRX2 daughterboard?
It's the sampling rate that the 100MS/s from the ADC get decimated
to. For example, you can set a 10MS/s sampling rate, and the USRP
will internally take the 100MS/s from the ADC, and filter them down
to 10MHz and decimate to 1/10th of the original rate.
The TVRX2 is a bit special compared to all other daughterboards
because it actually uses a real IF, all other daughterboards are
direct converters that give complex baseband. The samples that the
USRP sends to the host are all "pseudo-complex", ie. (sample_value +
j*0).
Or is this the bandwidth that is displayed on the QT Sink?
No, not inherently: You can configure any "sampling rate" parameter
in the QT Sinks, and that will do nothing but change the numbers on
the frequency axis. It doesn't have an effect on the signal, just on
the labeling.
I'm asking this because whenver I set it to say 400 kHz in
sampling rate, it give me a bandwidth of 400 kHz.
Not quite sure about that: As the TVRX2 is a 2x real IF device, the
USRP's FPGA is configured to give you a real sample stream --
meaning that the 400kS/s are real samples, and that the bandwidth
would be 200kHz.
For all IQ-demodulating direct conversion daughterboards (ie.
everything but TVRX, TVRX2, BasicRX/TX and LFRX/TX) you get complex
sampling, where f_sample == b_nyquist, but for real signals, Nyquist
dictates that the representable bandwidth is half the sampling rate,
remember?
If this sets the sampling rate in the usrp, it should only make
the plot nicier, not increase its bandwidth. If I am not mistaken.
Thanks in advance.
I don't understand -- obviously, increasing the sampling rate will
increase the bandwidth of a digital signal. That's the mathematical
effect of sampling.
However, the TVRX2 is among the very few daughterboards with
adjustable analog bandwidth -- you can select between 1.7 MHz, 6
MHz, 7 MHz, 8 MHz and 10 MHz of analog filter bandwidth.
Best regards,
Marcus
On 15.09.2015 18:11, Gerome Jan L wrote:
Hi guys,
What does the sampling rate in this usrp block does?i'm talking
about the uhd:usrp source block. Is this the one that samples the
IF from my TVRX2 daughterboard? Or is this the bandwidth that is
displayed on the QT Sink? Or is this the bandwidth that needs to
be sample. As far as I know, sampling rate is fixed at 100 MSps by
the ADC.
I'm asking this because whenver I set it to say 400 kHz in
sampling rate, it give me a bandwidth of 400 kHz. If I increase
does, it increases the bandwidth too. If this sets the sampling
rate in the usrp, it should only make the plot nicier, not
increase its bandwidth. If I am not mistaken.
Thanks in advance.
--
Best,
*Gerome Jan M. Llames *
Aspiring Technopreneur | Tech Savvy | Curious
Mobile: +639271525124 <tel:%2B639271525124>
Email: <mailto:geromejanlla...@gmail.com>geromejanlla...@gmail.com
<mailto:geromejanlla...@gmail.com>
"/Because the people who are crazy enough to think they can change
the world, are the ones who do./" - Steve Jobs
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