[Elecraft] K2/100 low power

Sat Apr 24 14:07:17 2004

Hi

This is usually caused by a miss adjustment of R26 on the KPA100. This =
adjustment is critical to the proper operation of the KPA100 and it is a =
little strange in its operation. You must bring the power up to 50 or so =
watts on the external watt meter then adjust R26 in tiny increments to =
make the display on the K2 display agree. Each time you make an =
adjustment you must move the power pot on the K2 a little one way or the =
other to make the K2 reread the ALC circuit. I usually just drop the =
reading a few watts and reset it to 50 watts. After I have it working at =
50 watts I check it at 100 watts and make a very tiny adjustment to R26 =
if required. I then check to see how it tracks up and down the scale at =
several points. R27 the reflected power adjustment should be set about =
20% higher than the forward pot. Just turn off the K2 and measure the =
resistance from ground to the wiper of R26 and set the wiper of R27 20% =
higher this should make the SWR meter work fairly close.

You can set the reflected pot better if you will make up two dummy loads =
of 25 and 100 ohms. I used 2 51 ohm 3 watt MOS resistors in parallel =
mounted in a pl259 for the 25 ohm and a 100 ohm 5 watt MOS resistor =
mounted in a pl259. Adjust the balance trimmer cap so you get the same =
SWR reading with either resistor then set R27 so the K2 displays 2:1 =
with either resistor. This should be done with about 5-10 watts and done =
quickly so you do not overheat the resistors.

Watt meters are notoriously inaccurate. I have the same meter you have =
and it is fairly accurate. I have several others as well (2 TenTecs, a =
OHR WM-2 and a HP 432B power meter) but I always use a 300 watt 40 db =
attenuator and a scope to set this calibration. This is the only method =
I trust. Most of the inexpensive wattmeters have an internal calibration =
pot and you never know if it is right or not unless you have a way to =
check it against a known accurate meter or other standard. Also just =
because it is "factory" made is no guarantee it is calibrated right. I =
have also been fooled because the battery was low on my OHR WM-2 and it =
was reading low. A battery test and power indicator LED would have been =
nice on this meter. I am always forgetting to turn it off running down =
the battery.

The Autek is a good meter except I never figured the reason for the =
reverse polarity on the power plug from just about everything else out =
there. Be careful with your K2 power plug and don't mix them up. They =
use the same plug but reverse polarity. I removed the power socket on my =
WM-1 and installed a pigtail with a powerpole connector on it so I can =
plug it into my RigRunner

Don Brown
KD5NDB

  ----- Original Message -----=20
  From: Andy Bullington<mailto:[email protected]>=20
  To: [email protected]<mailto:[email protected]>=20
  Sent: Saturday, April 24, 2004 11:35 AM
  Subject: [Elecraft] K2/100 low power

  I just got a new SWR/watt meter from Autek to use with the balanced =
antenna
  tuner I just built. It confirms my unease about my K2. It reads 100 =
watts
  out for my Omni V, 140 watts out for my Drake T4XB and a maximum of 75 =
watts
  on the K2/100. Not only that but the power jumps back and forth =
between 65
  and 75 watts. I use the K2/100 every day and get great reports on tone =
etc
  and have had no other problems. Any ideas? Thanks.

                   Andy W1AWB

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