[1000mp] ALC

[Tom McDermott]

Mike,

	You can run a fair amount of ALC on digital modes that only transmit
a single carrier at any instant in time - such as RTTY, MFSK, and CW. =
You
should not have any significant ALC on modes that transmit multiple =
carriers
simulataneously, or that shift the carrier phase suddenly - such as PSK,
Digtrx, MT63, etc.

	The reason is that ALC causes compression of the waveform. When
multiple tones are present, the compression will cause generation of
intermod products between the tones. If these IMD products fall in the =
audio
range they cause your signal to broaden a lot. What you get is more =
power
going into your interference products, and less power into your desired
signal.

	On phase-shifted signals, compression causes spectral regrowth,
which is seen on PSK as a really broad signal. The worst possible IMD on =
PSK
caused by ALC is -13 db - you see that a lot on the air.

	Some pointers on interfacing a soundcard to a transmitter:
http://www.tapr.org/~n5eg/index_files/page0005.html

	-- Tom, N5EG



> Picked up a Field exactly one week ago. The question
> I have concerns ALC action on CW and RTTY. I've read
> the manual and if it's in there I'm blind. Should the
> ALC just be ignored in these modes?
> =20
> Previous rigs I would turn up power till ALC was=20
> tickled and then back it down a bit.=20
> =20
> 73
> Mike WA2E