[Amps] alpha 87a and Pro II question

[Paul Christensen]

> The problem is setting gain/drive up too high and letting the
> ALC loop control everything.  This HAS to result in overshoot
> since there is a time constant in any feedback loop.  Proper
> selection of component time constants can reduce this but
> not eliminate the problem.

Unless a separate "Drive" control is accessible to the operator, it takes a 
dual-speed ALC loop to completely address the problem.  The trick is 
designing ALC to respond fast enough to inhibit leading edge power spikes, 
while preserving the RF waveform.  The effect is most noticeable on 
transceivers with inferior ALC design when operating CW.  The cheap fix for 
the manufacturer to eliminate the power spike issue is to drive ALC harder 
and use a faster response time.  But this results in waveform distortion.

I am now a firm believer in rigs with a separate Drive control.   On rigs 
with the control, or on rigs with no Drive control when using SSB, I never 
drive the radio into the ALC range -- rather, I find the ALC threshold and 
then just slightly advance for a slight indication of ALC activity.  On CW, 
this will often result is a very clean waveform (notwithstanding other 
factors as in the FT-1KMP) and thermal drift shouldn't become problematic.

I could never understand the rationale behind a manufacturer's instructions 
where they recommend ALC "anywhere within the red zone" for example.  On 
many rigs, the upper edge of the red zone results in extreme pre-PA gain and 
a lot of RF limiting.  Outside of maintaining constant power as a result of 
thermal drift, for what other reason is it necessary to drive the ALC so 
hard?

-Paul, W9AC