[Elecraft] ALC meter response question

[Andreas KU7T]

Very nice writeup, Ron.

I am not able to get a single LED flicker on 10 m although on 40 m there are
3 or 4 LEDs on (SSBA = 4, SSBC = 1). I am thinking about changing the 5.6k
resistor (MH2) to get more gain out.

My question:  Is it a problem if on a lower band the ALC must reduce a lot?
If I get a single LED to flicker on 10 m, I might have 5 to 6 LEDs flicker
on 40. Problem?

Thanks and 73
Andreas, KU7T




Original message:
That's perfectly normal, Andrey.

When you reach full RF output as requested by your setting on the POWER
control, the K2 ALC circuit "turns down" the gain to keep the power from
exceeding that level AND lights the ALC display bars.

So the moment ONE bar flickers, the K2 is putting out all the RF you are
requesting. If you have the POWER control set at 10 watts, it's putting out
its full rated RF power (unless you have the KPA100 working!). The number of
bars that light only indicates how much the ALC must reduce the transmit
gain to hold the power down to the level you request. That's why more bars
light when you reduce the power below 10 watts. 

You did not mention which band you ran the test on. The RF power output in
SSB mode is a function of both the audio gain AND the gain of the RF stages
in the transmitter. The gain of the RF stages in the transmitter is lowest
at 10 meters on most K2s, so I'd suggest you confirm that you get a little
flicker of at least the right hand bar on 10 meter SSB. 

You will also need a little more audio if you run compression. The higher
the compression, the higher the audio needed. So check the output on 10
meters at the highest compression level you are likely to use. If you are
still seeing at least a little flicker of one bar, you have plenty of audio
for full RF output.

With the bar graph in RF mode it shows "peak" SSB power output, so you can
also confirm that you have full RF output by watching the RF output too.
Keep in mind that the peaks of the audio waveform for speech are very brief
unless you use a lot of compression, so if you have the RF POWER set for 10
watts, the 10 watt bar will only flicker very briefly on occasional voice
peaks. That's normal and indicates full RF output. 

Ron AC7AC
K2 # 1289