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

[Enno J. Korma, PF5X]

Hi gang,
 
Apart from the fundamental discussion "do you really need ALC yes/no", I
have raised this issue already quite some time ago. I have an SPE 1K-FA and
K3 on order, and I want to work both full power barefoot as well as with the
amp, but do not want to run the risk to accidentally overdrive it.  A very
quick response from Wayne gave the following info. Sufficient to cool the
discussion for a while I would say ...
 
-- Enno, PF5X
<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.

External amplifiers vary widely in their loop gain, causing problems with
distortion. Many amplifiers, like the Alpha 87a, specifically say not to use
external ALC. A properly operating, internally ALC controlled rig like the
K3 does not need external ALC input to connect to an external amp. In
general, external ALC should -not- be used as a way to control rig power.

As for the voltage range, this is not a typo: the ALC input handles 0 to +5
V. Once ALC is working to our satisfaction, we'll provide simple interfacing
information that will allow the use of negative control voltages (probably a
resistive divider pulled up to a positive supply, or at most an op-amp
circuit).

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

73,

Wayne

N6KR

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