[Elecraft] Power too high in PSK31 / S

[Richard Ferch]

Well, I'll be doggoned!

Thanks, Joe - I seem to recall reading that somewhere, but I hadn't really
taken it in, and I was still using the procedure that worked with my
previous radio.

If I set the K3's requested power to 100 watts, then with 0 bars ALC I get
IMD well below -30 dB, but with even 1 bar it rises to -26 dB, and gets
worse with more bars. At the same time, the average transmitted power rises
above 50 watts - clearly the peaks are getting into compression.

However, if I set the requested power to 50 watts, I can push the ALC right
up to 4 or 5 bars while the average transmitted power stays at 50 watts on a
two-tone signal and the IMD stays below -30 dB. That's a safer and easier
way to operate.

So now to remember: in modes like CW and RTTY set the requested power to
100w, but in PSK and other similar modes cut it back to 50w. I can probably
figure out a way for my digital-mode software to remember this for me and do
it by software control.

Actually, I think I'll set it to some other number, such as 40w, to lessen
the risk of inadvertently recalibrating TX gain by hitting the TUNE button.

Thanks again, Joe.

73,
Rich VE3KI / VE3IAY
K3 #1595


> > So, no bars equals more noise and IMD or even one bar causes 
> > more IMD? 
> 
> My information comes directly from Lyle - I don't remember if 
> it was on the reflector or in a direct e-mail during testing 
> of some beta ALC code. 
> 
> > FWIW, I leave my K3's power control set at 100 watts, but I 
> > adjust the mic gain control to a setting which ensures I get 
> > zero ALC reading (even one bar causes a noticeable increase 
> > in IMD as measured on a PSKmeter)."
> 
> Setting the power out to 100 watts in PSK will guarantee that 
> the final is being driven into compression on peaks if you see 
> ALC (enough drive to reach 100 watts).  
> 
> I measure no difference in IMD with no ALC (just below the 
> point at which the first bar shows) vs. five solid bars if 
> the power level is kept below about 60 watts.  Put another 
> way, if the peak (CW equivalent) power level is kept below 
> about 60 watts to prevent compression (and the onset of IMD 
> generation) in the K3's finals, there is no difference with 
> ALC just below the level of the first bar and five solid bars. 
> If the mic/line gain is open just enough to get power output 
> the PSK has more noise, has about 1 dB more IMD, and power 
> output is less stable than with five bars of ALC.   
>   
> What Rich's procedure does accomplish is assure that the power 
> output does not exceed the 50/60 watt level.