Posted by
Don Brown-4 on
Feb 23, 2006; 1:30am
URL: http://elecraft.85.s1.nabble.com/Re-K2-Power-Callibration-tp386863p386865.html
Hi
I will throw my two cents worth. I agree with everything Don is saying here
however there are several other ways to get a reasonably accurate power out
measurement on a K2 or K2/100. The simplest and maybe least expensive is the
Elecraft DL1 dummy load kit. This dummy load will handle 20 watts and
includes a built in RF probe to measure the power out. You just connect a
voltmeter to the probe out test points and use the included graph to convert
the DC voltage to watts. Everyone building a K2 should have one of these
simple dummy loads/RF indicator kits for calibration and tune up.
Another method is to use the new Elecraft CP1 directional coupler/power pick
off. With it you can use a QRP watt meter like the OHR WM-2 to measure up to
100 watts. You connect the K2/100 to the CP1 and then out of the CP1 to a
dummy load that can handle 100 watts like the Tentec 300 watt load or the
OHR 100 watt load. Then the forward pick off from the CP1 goes to the WM-2
set on 1 watt if you built the CP1 for 20 db or the 100 mW range if you
built the CP1 for 30 db. The WM-2 will read 0-100 watts. If you don't have a
watt meter then you can do the same thing with a scope and a little math by
connecting the scope across the forward terminator resistor on the CP1. You
should be able to do the same with a RF probe and a DC voltmeter with the 20
db version of the CP1. The 30 DB version may have too low of output for the
30 DB version for use with a RF probe.
I also wrote an article several years ago on how to convert the OHR 100 watt
dummy load into a 100 watt Pi attenuator with a 20 db down output. This can
be used with a scope or QRP watt meter to measure 0-100 watts. I will repost
the instructions if anyone is interested.
Thanks
The other Don
Don Brown
KD5NDB
----- Original Message -----
From: "Don Wilhelm" <
[hidden email]>
To: <
[hidden email]>; <
[hidden email]>
Sent: Wednesday, February 22, 2006 6:42 PM
Subject: RE: [Elecraft] Re: K2 Power Callibration
> John,
>
> One must be careful not to zap the diode in the RF Probe - so measuring
> directly across the dummy load is good only up to 20 watts or so. A
> 'scope
> with a proper probe will handle the full 100 watts of the KPA100 easily.
> Builders may not have a known good 'scope, and the RF Probe method must be
> used with some intelligence - many folks do not know the accuracy of their
> dummy load at the frequency of operation - and both the 'scope and RF
> Probe
> methods are highly dependent on knowing the accuracy of the dummy load -
> it
> must be entirely resistive for accurate results.
>
> Yes, I feel that my 'scope and 1% 50 ohm dummy load (checked for both R
> and
> X on several antenna analyzers) will provide better than 5% accuracy for
> any
> wattmeter that I calibrate by that method. Of course, I can do a more
> accurate job at 30 watts or lower because I can read the voltage
> differences
> on my 'scope face with greater precision (the 10 volts per division scale)
> and at higher power, I end up at the 20 or 50 volts per division scale and
> the interpolation becomes more coarse.
>
> 73,
> Don W3FPR
>
> Elecraft web page:
http://www.elecraft.com>
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