[Elecraft] [KX3] Solid state amps and KX3 negative ALC

[Rick Tavan N6XI]

Good explanation as usual, Don. I think there may also be an another factor
in play: Back in the day, rigs had manual controls (e.g. drive, power, tube
amp plate/load controls, etc.) and it was pretty easy for a busy or
distracted operator to position them incorrectly and overdrive an external
amplifier, especially when changing bands or making long QSYs. Maybe
protective ALC was justified in those cases, although I never used it and
never got into trouble. Modern, solid state rigs such as the KX3 and K3
don't have manual tuning controls to mis-set and can memorize desired
output levels on a per-band basis. It is far less likely today to make the
kinds of mistakes that used to suggest a need for ALC protection. So now,
more than ever, it seems unnecessary and possibly inadvisable to use
external ALC. It has always been best to adjust output appropriately to
prevent over-driving an external amp. Now it's easy, too.

/Rick

On Sat, Jan 5, 2013 at 5:47 AM, Don Wilhelm <w3fpr at embarqmail.com> wrote:

> 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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-- 
Rick Tavan N6XI
Truckee, CA