On 11/11/2010 10:21 AM, dave wrote:
Kevin Alfred Strom wrote:


There's a growing number of amateur operators, experimenters really,
using the AM mode on shortwave, too. You can find them on
3700-3735 kHz,
3860-3890 kHz, 7285-7295 kHz, and a few other spots too.

What's interesting about them is that some are real experimenters and
run transmitters with superb fidelity, some sounding better than
commercial broadcast stations.


With all good wishes,


Kevin, WB4AIO.

What's experimental about A3 emission?



That's like asking "What's experimental about audio?" The answer is:
an almost infinite number of things.

Some things with which I or my friends have been personally involved
that relate to AM experimentation:

1. Building new kinds of AM/DSB detectors, including ultra-low
distortion detectors, synchronous detectors, stereo (I/Q and U/L)
synchronous detectors, autocorrelation detectors, et cetera.

2. Refining and extending the state of the art in AM transmission,
including Class E and Class D transmitters, pulse-duration
modulation, multiphase pulse duration modulation, I/Q multichannel
modulation, outphasing modulation, use of mathematical transforms
for AM/DSB generation, et cetera.

3. Study of the effectiveness of wider-bandwidth modes with varying
degrees of information redundancy in varying communications
conditions, including AM/DSB versus SSB (the late John Costas,
W2CRR, an amateur AM operator and experimenter, was the pioneer
here, with his "Poisson, Shannon, and the Radio Amateur" in
_Proceedings of the IRE_).

4. Experimentation with audio processing, including multiband AGC,
compressors, distortion-cancelled clipping, audio phase rotators, et
cetera (one of the pioneers in this field, Mike Dorrough, is an
amateur AM operator).

I am sure there are many more examples of AM experimentation than I
am even aware of. It's a mode that seems to attract those with an
experimental bent. Very few AM hams are running stock commercial
gear; usually, at the very least, it is modified for better quality
audio.

Hearing the best of these operators on a receiver with superb audio
-- say, an SP-600 in the 13 kHz bandwidth, with the detector output
fed into a high-fidelity amplifier driving a pair of AR-3ax speakers
-- brings you the true magic of radio in a way that must be heard to
be believed.


With all good wishes,


Kevin.
--
http://nationalvanguard.org/
http://kevinalfredstrom.com/