[Elecraft] ALC: issues raised almost 2 month ago + answer from Elecraft

[Jerry Flanders]

At 02:59 PM 12/3/2007, Enno, PF5X wrote:
>Hi gang,
>
><SNIP> A very
>quick response from Wayne gave the following info. Sufficient to cool the
>discussion for a while I would say ...
>

Not so - Wayne's comments seem directed at those who might want to 
use ALC as if it were a substitute for the mike gain control.

It worries me when I see the discussion wander away from amplifier 
safety in an antenna catastrophe situation, which is my main concern. 
I once blew up the output circuit of an AL1200 due to an intermittent 
in an antenna coax while running full power on RTTY.

Please see my other in-line comments below.

>--
><quote>
>
>From: wayne burdick n6kr at elecraft.com
>
>Date: Fri, 12 Oct 2007 14:12:24 -0700
>
>To: elecraft at mailman.qth.net, cw at dx.nl
>
>Subject: regarding external ALC
>
>
>
>Hi Enno,
>
>Transmit power control via the ALC input (AUX I/O pin 15) is planned, but
>not finalized. We're mindful of the negative impact ALC can have on transmit
>signal purity, a subject of recent debate within testing organizations.

Speaking only for myself, I do not intend to adjust the ALC to 
provide normal level control - only a crisis shutdown function. 
Quoting from my Quadra's manual p4.:

"The ALC cable must be connected between
the transceiver and VL-1000 to
prevent overdrive of the amplifier, and especially
to facilitate the proper operation of the
protection circuitry if sudden antenna system
problems should cause the SWR to rise to dangerous
levels."

Rightly or wrongly, Yaesu (and probably ICOM) engineers have presumed 
the ALC would be functional and could cut back exciter drive in the 
event of an antenna catastrophe. Other main-line rigs that I am 
familiar with are compatible. I think it is reasonable to assume the 
world-class K3 would have provided for this also.

BTW - It is worrisome that ALC was only planned, but still not 
finalized, as of Oct 12.

<snip>
>  Once ALC is working to our satisfaction, we'll provide simple interfacing
>information that will allow the use of negative control voltages ...

I, and perhaps other Solid State amp users, would prefer a definite 
calendar commitment, if that is possible. If not possible, please 
state so. I would hope for a working, properly engineered 
negative-going ALC fix within a few months.

>Meanwhile, the K3's DSP-based early-stage ALC is very effective at
>preventing amplifier overdrive, and should suffice in nearly all cases.

I repeat -  my concern is amplifier safety, not a substitute for a 
mike gain control. Sooner or later, the antenna will fail, but we 
don't know when,  and we probably cannot manually cut back drive 
quickly enough to protect those expensive SS finals when it occurs.

>73,
>
>Wayne
>
>N6KR


Jerry W4UK