[RTTY] K3 AFSK power and ALC?

[Richard Ferch]

Steve,

Not to worry on several counts:

1. The K3's "ALC" meter is unusual in that the first 4-5 bars are not 
measuring ALC at all. That part of the meter range is more like a VU 
meter, and ALC only kicks in at higher readings.

2. The K3's ALC is slow-acting, and it does not have the same impact on 
quality of signal as a fast-acting ALC would. Actually, the K3's power 
control works better with a few bars showing on the ALC meter. With no 
bars showing, the power control is not as stable.

3. Even in PSK31, which is very sensitive to IMD and requires good 
linearity, the K3's output is clean even with 5 bars of ALC showing on 
the meter. The critical adjustment on the K3 for PSK31 is not the mic 
gain, it is the transmitter power. You have to keep the power below 
about 50-60 watts in PSK31; higher powers can result in clipping and 
therefore IMD, regardless of the ALC meter reading.

4. RTTY does not require linearity. Like CW, you can run RTTY with a 
Class C (non-linear) amplifier. The main issue with RTTY is not 
linearity, it is keying transients at the frequency shifts (the RTTY 
equivalent to key clicks). In AFSK, keying transients are controlled by 
the software or hardware that generates the audio, not by the radio.

5. I have done a test with spectrum analyzer software on the output from 
my K3 using MMTTY. At 100 watts output, with 5-6 bars of ALC in AFSK, I 
found that my K3's transmitted signal in AFSK was actually cleaner than 
it was in FSK.

73,
Rich VE3KI


> Wow, the big news is I have a K3 -- I bought one of Doug's (ZP6CW). Now
> to get ready for the big contest! I won't have the FSK working in time,
> so will be running AFSK.
>
> The usual instructions are to advance the mike gain to JUST BEFORE there
> is any ALC indication -- worked fine with my FT757. But the technical
> notes for PSK on the Elecraft site say to set power level to whatever
> (20-30 watts) and advance the mike gain to where "3 or 4 bars of ALC"
> are indicated. This will result in a very clean signal. No special
> instructions for AFSK RTTY are given.
>
> Can a K3 user help me? Would this work (actually, it does work but I
> don't know how clean the signal is): Set the power to 75 watts, fire up
> a CQ macro into a dummy load, and adjust the mike gain to "3 or 4 bars"
> of ALC reading?
>
> With a little more power available I hope to go high and call CQ, for
> once! See you in the test.

Steve ZP9EH wrote: