Re: K3 ALC Interface

Eric Swartz - WA6HHQ, Elecraft

Hi Guys,

I apologize for any confusion regarding external, negative going, ALC
usage with the K3. I'll try to clarify a bit here. (I would have
replied earlier, but I only get the time to read this list once every
2-3 weeks or so. I mainly focus on the Elecraft email list that we
host. - We're pretty busy at
Elecraft HQ getting K3s out the door these days. ;-)

While we, and many linear amplifier manufacturers, do not recommend
connecting the ALC line between the AMP and rig, for those that feel
the need to still use ALC on their K3 to AMP connection, we'll provide
a simple K3 mod to allow negative going ALC to be used. (It looks like
a couple of resistors and one diode will do it.)

I'll personally take the blame and apologize for this one. I'm not a
believer in ALC usage between unmatched amplifier-rig combinations as
it can create more problems than it solves. The ALC input on many rigs
is a vestige for possible use with -matched- amplifiers provided by
the same manufacturer.

We did not provide ALC input on the K2 and were not aware of a major
need for it as we have not had any complaints about it with over 6,500
K2s shipped. We really only added the ALC line on the K3 ACC connector
for possible future use with a matched Elecraft amplifier that might
be offered by us in the future. (No, this is -not- a product
announcement. :-) In that case it was planned only for use to reduce
the power to the AMP when the auto-tuner in the amp needed retuning.
Hence the non-standard +5V range.

I guess that since there are connections for ALC on many amplifiers
and rigs, many hams feel the need to connect them, even though it is
not necessary or recommended in most cases. To be honest though, using
the ALC signal from a random amplifier (not made by the -same- radio
manufacturer) to control a radio's output is fraught with severe
potential problems. Because each different amplifier's ALC control
voltage generation circuitry has totally different gain and time
response characteristics, is it impossible to guarantee an accurate or
fast enough power reduction response from the radio to ALC voltage
input. In most cases using ALC feedback with the drive power turned up
above the minimum needed level for the amplifier results in power
overshoot and clicks on CW and splatter on SSB. Personally I have not
used the ALC line from amplifier to rig for the past 30 years and have
had no problems.

That said, I can see that there are cases where -careful- usage of ALC
might be beneficial for some users who are careful to check for and
avoid external ALC loop feedback problems. We'll make sure we
accommodate you. Sorry about that!

73, Eric WA6HHQ

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