[Hackrf-dev] FM Receiver and offsetting frequency

[Jordan Kagan]

Exactly what I was looking for.  Thank you!

-Jordan

On Thu, Aug 20, 2015 at 3:05 PM, Dominic Spill <dominicgs at gmail.com> wrote:

> On 20 August 2015 at 15:42, Jordan Kagan <jrkagan2 at gmail.com> wrote:
> >
> > So in short I am wondering why one wouldn't just choose the center
> frequency
> > to be the FM channel frequency or a frequency in the range of interest.
>
> A great question and one that causes confusion for many people.  It's
> discussed in the HackRF FAQ, but from a different angle (i.e. "how do
> I solve problem X?"  "offset the centre frequency").
>
> If you start gqrx or any other tool that shows an FFT of the received
> data, you will notice a large spike in the centre of the display.
> This is the 0Hz component of the received signal, also known as the DC
> offset or DC bias.  It's a side effect of the quadrature sampling
> technique and is just something that we have to live with.  This is
> discussed here:
>
> https://github.com/mossmann/hackrf/wiki/FAQ#what-is-this-big-spike-in-the-center-of-my-received-spectrum
>
> The following FAQ question is about how to deal with it:
>
> https://github.com/mossmann/hackrf/wiki/FAQ#how-do-i-deal-with-the-dc-offset
>
> The tl;dr of that question is: offset the centre frequency of the
> radio and then shift it back in software.  This is what those
> flowgraphs are doing.
>
> I hope that answers the question, although if you would like more
> detail, I'm sure someone on this list can answer it better than I can.
>
> Thanks,
>   Dominic
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://pairlist9.pair.net/pipermail/hackrf-dev/attachments/20150820/5f242b28/attachment.html>