Re: [Discuss-gnuradio] Sampling rate / frequency issue

[Ellie White]

Hi,

Sorry, just realized that decreased bandwidth = decreased signal to noise. Had a memory slip on that one! But I am still interested in the main part of the question.

Thanks in advance!

Ellie

On Sat, Jul 15, 2017 at 11:13 AM, Ellie White <address@hidden> wrote:

Hello!

 

I have a quick question to ask, related to sampling rate and observed frequency on the waterfall sink. I’ve been testing an antenna (connected to an SDR dongle) with both GNU Radio and SDR#, and have noticed something kind of odd. In SDR#, I can see some strong signals at ~125040 kHz (125 is my LO frequency, so the actual signal is at 40 kHz). In GNU Radio, if I set the sampling rate to 2M, everything matches up with the SDR# display, but if I set it to a lower sampling rate, say 800k, the same strong signal shows up at 125031 kHz. Why is that?

 

The reason I would like to know is that I want to use a smaller bandwidth for this flowgraph, to increase S/N. Is there a way to decrease sampling rate – and thus bandwidth – without distorting the placement of the signals?

 

I’ve included my flowgraph, in case that would be of any use. Thanks so much – have a good day!

 

Ellie

 

p.s. Hopefully this doesn’t post more than once – it wouldn’t deliver from my other email address, so I sent it from this one.