[Elecraft] KPA100 power question..

Wed Dec 11 16:25:03 2002

Hi

This is a tricky adjustment. You need to slightly re-adjust the power
control after each very small adjustment of R26 or you can go out of and
into tune after each adjustment. By doing this you make the firmware
readjust the ALC. The idea is to set 50 watts on the external wattmeter and
then move R26 in small steps so the K2 display reads the same as the
external wattmeter. Check it at 100 and 10 watts also.

The external wattmeter needs to be accurate and many are not, so if you have
a scope you can check the wattmeter by reading the peak to peak voltage
across the dummy load. 10 watts will be 63.3 volts across the 50 ohm load 50
watts will be 141.4 volts across the 50 ohm load or 100 watts will be 200.0
volts across the 50 ohm load. Of course the dummy load needs to be accurate
also for this to work.

One very accurate meter I use is the OHR WM-2 QRP meter with a modified OHR
100 watt dummy load to change it to a 100 watt 20 db attenuator. One watt
full scale on the meter is 100 watts out. I described the modifications on
an earlier post but if anyone is interested I will repost it. It only
requires one resistor and a BNC connector.

Don Brown
KD5NDB

----- Original Message -----
From: "Jay & Jac" <[email protected]>
To: <[email protected]>
Sent: Wednesday, December 11, 2002 2:04 PM
Subject: [Elecraft] KPA100 power question..

> Hello all,
>
> I just completed the KPA100 on K2 #279.  All went well until I did a power
> output calibration at 50 watts at a friends house who has an accurate
> wattmeter.
>
> The problem is I cannot seem to adjust R26 to match the actual 50 watts
(as
> shown on the watt meter) to the power control on the K2.  The power
control
> pot on the K2 shows 12 watts lower than is actually being put out
> consistantly throughout it's upper range.
>
> Have I made a cockpit error somewhere?
>
> Jay, W6JDB
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