[Elecraft] K3 Mic Gain vs ALC

Don Ehrlich ehrlich at clallambroadband.com
Sun Apr 6 18:37:58 EDT 2008


I know I'm going to figure this out only *after* I break down and ask for 
help ... but I gotta ask anyway I suppose.

I have the K3/100 and an MH2 microphone and I am measuring output power with 
a calibrated scope across a dummy load.
I have been setting up audio gain and compression as instructed (With comp 
off set mic gain for 5 bars, then increase comp to fill in the waveform...). 
I have always before observed that, with compression set to zero the peaks 
of output come up to the power that I have set (or nearly so) but with 
relatively little in between the peaks.  With compression added the waveform 
filled in at, more or less, the commanded output power.  This is what I have 
always expected but today it is not happening that way.

Today, for the first time in quite a while, I notice that what I had been 
accoustomed to seeing no longer occurs.  With compression off I can adjust 
the mic gain for 5 to 6 bars ALC as usual but the peak rf envelope never 
gets close to the commanded output of 100 watts.  If I press TUNE the full 
100 watt carrier appears but I cannot get peaks to rise much past 50 watts 
with input from the mic.  With compression the waveform fills in with RF but 
the level is stuck at about 50 watts and ALC is still reading 5 bars or 
more.  It does not matter whether I have the audio chain set to High or Low 
gain .. most of my testing has been with the usual "FP.L bias" setting but I 
have tried High and also tried other microphones.

I notice that, after not speaking for a few seconds, if I make a sudden 
sharp noise the output does spike up to 100 watts but is quickly clamped 
down by ALC so that furthur loud sounds into the mic produce only about 50 
watts.  To make a long story shorter ... When SSB output is set for 100 
watts I only get about half that even though the ALC is showing 5 or 6 bars. 
The same is true with a setting of 50 watts or 12 watts where peak output is 
about half of the setting and I am seeing 5 or 6 bars ALC.  The audio sounds 
fine in the monitor and signal reports are good.   All of this occurs on all 
bands and I see the full 5 or 6 bars ALC even in Test mode with no RF 
output.

I'm running the latest 1.78/1.58  firmware which I downloaded last week.












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