An ALC won't introduce any more sidebands to PSK-31 signal than the amount
of sidebands it would add to a CW signal in the form of additional key
clicks over and above those caused by the initial generation of the pulse.
While this is a problem on radios like the older FT-1000 MKV's, it has never
been reported as a problem with TT and specifically with Orions. In fact,
the Orions seem to have just the opposite problem: a fairly slow-acting ALC.
Ron N6IE
www.N6IE.com
(Formerly N6AHA)
----- Original Message -----
From: "Merle Bone" <merlebone@charter.net>
To: <tentec@contesting.com>
Sent: Friday, December 29, 2006 5:40 PM
Subject: Re: [TenTec] TX EQ = -14 dB for PSK31
> Ron Castro (N6IE) said:
> "Since PSK-31 works by shifting phase, the amplitude variations caused by
> ALC
> shouldn't have any significant effect on either the IMD or readability of
> this signal."
> ------------------------------------------------------------------------------------------------------------------------
> Ron, we are going to have to disagree on this one. Anytime you introduce a
> nonlinearity into the system producing PSK31 signals you will generate
> unintended sidebands. You may do that by overdriving the audio stage or
> the PA , or you can do that by introducing any nonlinearity into the RF
> amplifiers, including the final stage. Certainly, massively overdriving
> the signal, as you described, is one way to cause a problem. Of course,
> using speech processing - which introduces distortion into the signal, -
> will also cause serious sideband distortion and excessively wide signals.
> The problems caused by ALC making the final non-linear is probably a
> function of how much ALC action is invoked. But I think any distortion
> isn't helpful in this mode and creates a wide signal that isn't
> appreciated by other users.
>
> This is a pretty good presentation on PSK and tuning a rig (Worth looking
> at) http://kk7uq.com/html/download/IMD%20Presentation.pdf . I think you
> will always find that papers on this mode recommend low, or if possible,
> NO ALC action.
> 73. Merle - W0EWM
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>
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