[Elecraft] Elecraft RF Probe

[Stan Rife]

	Thanks, Ron, and everyone. I am trying to measure the RF voltage at
the dummyload, and calibrate the K2 RF meter. The probe is fine at 20watts,
what everyone has recommended I check it at. I was just trying to read it at
100watts to verify that the K2 meter tracked with the output. That's when I
took out the diode. 

	Tom and Don both warned me about this, but I just had to push the
envelope. I'll just set it at 20watts and let it go at that. I'll see if I
can find some 1N34A diodes locally.

	The voltages range from 25v to 70v. 71 volts equals 100.8 watts, if
I remember my calculations. 



Stan Rife
W5EWA
Houston, TX
K2 S/N 4216
 

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Ron D'Eau Claire
Sent: Monday, May 22, 2006 9:20 PM
To: elecraft at mailman.qth.net
Subject: RE: [Elecraft] Elecraft RF Probe


As you make the RF probe better able to handle high RF voltages you will
also cause it to be less accurate at lower RF voltages.

The common RF probe diodes have a turn-on voltage of about 0.2 volts. Below
that, they are almost open circuits and have no output. Higher PRV diodes
have turn-on voltages of closer  to 0.6 volts - three times that of the more
sensitive diodes. So it takes three times the RF voltage to even begin to
show a DC output and you'll need to be well above the turn on voltage to
show an output that accurately indicates the RF applied. Put two or three
diodes in series and you'll need 1.2 to nearly 2 volts  to just start
showing some indication of an output.

Bottom line, don't try to use such a probe for low RF levels.  

Ron AC7AC

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