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
---
http://www.elecraft.com
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