Forum: GNU Radio Quadrature rate question

A recent post by Markus Gonser had me intrigued and so I experimented
with his grc code. The resulting FM receiver does work but it doesn't
quite sound right. My guess is that the quadrature rate is not correct
at 705.6kHz. Is this the correct rate and if it's not what should it be?

A Google search didn't turn up anything that I could plug into my 
receiver.

On Mon, Dec 10, 2012 at 09:44:29PM +1000, Phil wrote:
> A recent post by Markus Gonser had me intrigued and so I
> experimented with his grc code. The resulting FM receiver does work
> but it doesn't quite sound right. My guess is that the quadrature
> rate is not correct at 705.6kHz. Is this the correct rate and if
> it's not what should it be?

That depends. The quadrature rate is the rate of the incoming I/Q sample
stream. 705.6 kSps seems unusual, though.

MB

--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

On Mon, Dec 10, 2012 at 01:05:13PM +0100, Martin Braun (CEL) wrote:
> On Mon, Dec 10, 2012 at 09:44:29PM +1000, Phil wrote:
> > A recent post by Markus Gonser had me intrigued and so I
> > experimented with his grc code. The resulting FM receiver does work
> > but it doesn't quite sound right. My guess is that the quadrature
> > rate is not correct at 705.6kHz. Is this the correct rate and if
> > it's not what should it be?
>
> That depends. The quadrature rate is the rate of the incoming I/Q sample
> stream. 705.6 kSps seems unusual, though.

Actually, it's 16*44.1kSps, which isn't that unusual. Still, you need to
get that rate at the input.

MB
--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

On Mon, Dec 10, 2012 at 7:40 AM, Martin Braun (CEL) 
<martin.braun@kit.edu>wrote:

>
> Actually, it's 16*44.1kSps, which isn't that unusual. Still, you need to
> get that rate at the input.
>
> MB
>

Yeah, if you're using a UHD device, you'll ask it for a specific rate. 
If
it can get that rate, everything's fine. If you are asking it for a rate
that it cannot achieve, it will give you a warning that you asked for 
rate
X but it was actually set to rate Y. If that's the case, you'll have a
sample rate mismatch between the two devices. You'll need to do some
resampling to get them to match.

Tom