[Elecraft] Keying Waveform Measurement

[Stephen W. Kercel]

Hi Roger:

Actually, I'm quite happy with my 46.1 Ohm reading. After 28 years of 
mysterious chemical reactions, my Cantenna impedance is still well within 
10% of its nominal value. I wonder if a brand new MFJ dry dummy load would 
be that close.

My Cantenna also contains the Heath-recommended transformer oil. It is (was 
back then anyway) readily available from commercial electrical suppliers. 
(BTW, I hope yours is not using askarel; it contains PCBs. Although it was 
illegal to use askarel in 1978, Heath still published performance figures 
for Cantennas filled with askarel.)

Although I see no present need to overhaul my Cantenna, I'd definitely be 
interested in seeing your pictures. If there is a way to post them to the 
reflector, I expect that other participants would like to see them as well.

You do raise a valuable caution. Cantenna impedance values apparently range 
fairly widely over the map. If people are trying to measure the power out 
of a K2 (or whatever rig) by using a voltage measurement and assuming a 
50+J0 load impedance, they should only do so if the measurements of the 
impedance of their specific Cantenna are close to that value.

73,

Steve
Way Down East and bracing for the Nor'easter of '05
AA4AK


At 07:48 PM 2/9/2005 -0800, you wrote:
>Hi Steve,
>I have never changed the oil either, mine is actual transformer oil as my
>father worked for the local utility company as the time.
>I was having KPA100 difficulties and decided to attach the MFJ analyzer to
>the cantenna just to check it out...imagine my surprise when it read 68
>ohms. I then put the leads from my Fluke dvm on it and it read the same.
>So what I thought was 50 watts was really 36....using P = V^2/50 and in this
>case 50 was really 68.
>I have the unit apart, there is a deposit of some kind on the body of the
>resistor. One has to reverse assemble the resitor holder from the lid in
>order to get it all apart. I am going to take photos of the unit if you are
>interested in seeing what I have.
>
>I since borrowed a Bird dummy load, 51.2 ohms and a Bird wattmeter and now
>have the KPA100 & KAT100 all recalibrated as well as found one end of C5C
>not soldered!! Smooth sailing now!!
>
>73, Roger WA7BOC, way out here in Montesano, WA.
>and on the home e-mail address!
>
>-----Original Message-----
>From: elecraft-bounces at mailman.qth.net
>[mailto:elecraft-bounces at mailman.qth.net]On Behalf Of Stephen W. Kercel
>Sent: Wednesday, February 09, 2005 2:05 PM
>To: elecraft at mailman.qth.net
>Subject: RE: [Elecraft] Keying Waveform Measurement
>