Keith,
With the power output limited to 12 watts, there should be no need to
connect anything to the ALC on your amplifier. That is just not
available on the KX3, nor is it available on any other QRP transceiver
that I know about.
Amplifiers historically provided ALC to throttle the power output from
the transmitter back when a given level of drive was received. That
worked fine in the old AM and CW days where non-linearity in the
transmit path could be tolerated, but with the advent of SSB where
linearity had to be maintained in the transmit path, this method became
a recipe to create distortion and splatter on the air. Consider that
there is a finite time delay between detection of an overdrive condition
and that ALC signal back to the transmitter to reduce its power level.
In other words, the overdrive condition had to already be present before
the ALC could do anything about it.
There is one manufacturer who claims his ALC action is so fast that
there will be no distortion or splatter, but I have great doubts about
that - he would have to predict an overdrive situation before it
actually happened, and I am not sure how that would be accomplished.
Recently, some solid state amplifiers added a new twist. They have
incorporated sensing circuits to indicate a fault condition such as a
high SWR condition, then the use the ALC line to reduce the transmitter
power to a safe level. While that is a noble goal, I often wonder why
any amplifier with that complexity would want to depend on some external
driver to protect itself. I guess cost is the answer, but depending on
something external to "do the right thing" always has puzzled me. If
the amplifier has enough smarts to detect fault conditions and considers
those faults to be worthy of protecting the amp, then why do they not
include circuits to dump the drive power into a dummy load instead of
the amplifier input - and eliminate the requirement for ALC - the KPA500
goes to standby when it detects a fault and I do not understand why
other manufacturers do not do the same.
OK, that ends my occasional rant on ALC.
Happy New Year
73,
Don W3FPR
On 1/5/2013 8:10 AM, Keith Heimbold wrote:
Please excuse me for my newbieness in asking this question but it has been on
my mind for awhile now. I am the proud owner of KX3 847 and am curious about
the need for Negative ALC capability and interface for the KX3 as I connect it
to my solid state amplifiers.
I have been looking at the manual and thinking about interfacing the KX3 with
my two solid state amplifiers, THP HL450 and the yaesu Quadra. Both recommend
use of negative ALC connection from the transceiver. For my K3, the negative
ALC mod satisfies the Quadra in this respect.
I am looking for reference of negative ALC for the KX3 and cannot seem to
locate such a capability and interface. If it is in the manual my apologies for
taking up reflector space please let me know which page I am overlooking. If
not, then my assumption is that because of the low level of power output 12W
max, it was deemed not necessary to have this in the KX3.
Please let me know if I am on the right track so I can finally feel comfortable
interfacing the KX3 with my amps.
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