[Elecraft] K2/100 power-out change

[W3FPR - Don Wilhelm]

OK Folks,

I found the info that Tom was referring to - it is in a reflector posting 
from Wayne Burdick dated 8/5/1999.  I have appended the text to the bottom 
of this reply.

73,
Don W3FPR

----- Original Message ----- 

> It IS in the software ALC... reflects the ALC's attempting (at about a 
> 1-seconds rate) to 'stabilize the output at the requested power level...
>
> Seems I recall there being a fairly simply remedy to this problem... at 
> least to remedy MOST, if not all, of it.
>
----------------------------------------------------------------------
8/5/1999 post by Wayne Burdick:

THIS APPLIES TO ALL K2s.

Background
----------

When pressing TUNE, the power displayed typically varies over a range of
about +/- 0.5 W at the 5 W level. The actual variance depends on power
level, band, load, and supply voltage. The varieance is generally wider on
40 and 30 meters.

There are two reasons for the power not staying at exactly the level you
specify. First, some heating of the final transistors occurs that may cause
power to drift upwards a small amount during TUNE; this is normal. Second,
power is controlled by an 8-bit D-to-A converter, which has limited
resolution. In other words, each DAC step may translate to as much as a few
tenths of a watt on some bands at 5W.

This small variance in TUNE power level is not significant in terms of
actual radiated signal. The difference between 4.5 W and 5 W, for example,
is less than 0.5 dB. However, it may be possible on a particular K2 to
reduce the variance with a simple component change.


What to do
----------

NOTE: This change is completely OPTIONAL! It may result in a reduction of
the maximum power that you can put out on the higest bands, especially
under high-SWR conditions.

1. Test TUNE at 5 W working into a 50-ohm dummy load on 40 m. If pressing
TUNE repeatedly results in a power output reasonably close to 5 W each
time, there's no need to do anything.

2. If you have a Field-test K2 (S/N 1-100), the next step is to replace R99
on the RF board with 270 ohms (if you haven't already done so). This
resistor was 470 ohms on the field-test units.

3. Temporarily insert a 1K potentiometer at R98 (use leads of 1" or less).
Set the pot to mid-range (500 ohms).

4. Switch to 10 meters and set power for 10 W (or your desired maximum
power output on 10 meters).

5. Your goal is to find the largest value of R98 (up to 1 K) that allows
for the desired maximum power output on 10 meters using TUNE. Try various
R98 settings until you find this value.

6. Once you've found the highest usable value for R98, switch back to 40 m
and see if this has improved power-setting resolution using TUNE at 2 W, 5
W, etc.

7. Replace the pot at R98 with a fixed resistor. Use a standard resistance
value that is equal to or lower than your final pot value.