[Elecraft] Re: K2 Power Callibration

Wed Feb 22 21:25:24 EST 2006

I have to slip a plug in here for my new wattmeter kits... specifically 
the LP-200 dummy load/wattmeter. You can read about it at 
www.telepostinc.com. It's like a DL1 on steroids. It includes a 30W 
dummy load, with a variable speed fan option for 100W continuous rating. 
It doesn't get nearly as hot as a DL1, even without the fan, but more to 
the point, it's microprocessor controlled, has digital readout, 
frequency and temperature compensation, and will accurately display 
power from 1mW to 120W. It makes a great addition to any bench. I 
started shipping these about a week ago.

I also have a handheld digital wattmeter (LP-300) for field use that 
will work at QRPp thru 100W that's real slick and will be out in a few 
weeks, and a high-end digital meter (LP-100) that will go on sale this 
week, that is based on my cover article in the Jan/Feb QEX. One unique 
feature of the LP-100 is the ability to display complex impedance, in 
addition to lots of other professional features.

The LP-100 and LP-300 feature a nifty peak responding bargraph display 
that will follow voice peaks, and display power and SWR simultaneously 
in both analog and numeric form. The LP-300 can not only be used for 
antenna tuning, but as a realtime monitor for field operating. It has a 
battery life of 25-100 hours depending on type of battery and backlight 
usage. It also has a 12v jack for external power. The LP-100 uses a 
superfast PLED display, and has lots of unique features.

They're all kits, and cover a range of needs. There are links to all 
three on the above webpage, as well as a link to a comparison matrix of 
the three. I will be at Dayton  with a booth showing these and more.

Larry N8LP
ww.telepostinc.com

Don Brown wrote:

>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" <w3fpr at earthlink.net>
>To: <jferg977 at aol.com>; <elecraft at mailman.qth.net>
>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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