AM Stereo TX? (Motorola C-QUAM)

GNU Radio
1

I have been Googling a good deal and have not come up with much. I have
done numerous projects with GNURadio, but while I can throw together a
wideband AM transmitter, I cannot figure out the stereo portion. Based
on
what I know; it is some kind of phase-modulated information.

Anyone know how to get started on a flowgraph, or maybe some code
examples?

Thanks. :slight_smile:

2

On 03/24/2014 07:59 PM, Jordan J. wrote:

Discuss-gnuradio mailing list
[email protected]
Discuss-gnuradio Info Page
I don’t think I’ve ever heard of anyone making this query before. You
should probably start with whatever public documents describe the
Motorola system, and go from there.

3

Marcus,
Here’s what I found, with a google image search, there are some
interesting images and discussions of the modulation techniques there
with both block and flow diagrams.

This one seems very interesting and probably makes it similar to what
might have to be done with gnuradio.
http://jsgil.mylinuxisp.com/AM-Stereo/QuadMod-4Way.gif

http://www.morpheustechnology.com/ebooks/Wireless/03%20Amplitude%20Modulation.htm

The basic idea behind the C-Quam modulator is actually quite simple. The
output stage is an ordinary AM modulator however; the carrier signal has
been replaced by an amplitude limited vector modulator. Therefore, the
limiter output is really a phase-modulated signal.

A standard AM receiver will detect the amplitude variations as L+R. A
stereo receiver will also detect the phase variations and to extract
L‑R. It will then process these signals to separate the left and right
channels.

To enable the stereo decoder, a 25 Hz pilot tone is added to the L‑R
channel.

Hope this helps.
Bruce

From: Marcus D. Leech [email protected]
To: [email protected]
Sent: Monday, March 24, 2014 5:11 PM
Subject: Re: [Discuss-gnuradio] AM Stereo TX? (Motorola C-QUAM)

On 03/24/2014 07:59 PM, Jordan J. wrote:
I have been Googling a good deal and have not come up with much. I have
done numerous projects with GNURadio, but while I can throw together a
wideband AM transmitter, I cannot figure out the stereo portion. Based
on what I know; it is some kind of phase-modulated information.

Anyone know how to get started on a flowgraph, or maybe some code
examples?

Thanks. :slight_smile:

Discuss-gnuradio mailing list [email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
I don’t think I’ve ever heard of anyone making this query before. You
should probably start with whatever public documents describe the
Motorola system, and go from there.

–
Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium