[Elecraft] regarding external ALC

[wayne burdick]

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

> Scanning through the manual I saw that the ALC voltage to be applied 
> on pin
> 15 of the ACC connector needs to be in the 0 - +5V range. This worries 
> me a
> bit because many (if not virtually all) linear amps output a NEGATIVE 
> ALC voltage for
> feedback to the transceiver.
>
> Is the +5V maybe a typo (i.e. should it be -5V) ??
>
> -- Enno, PF5X


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