Posted by
Francis Belliveau on
Jul 25, 2006; 3:38am
URL: http://elecraft.85.s1.nabble.com/Funny-power-measurements-tp392406p392409.html
Okay, I guess I left out some critical details from my original post.
I am using a 50 ohm load that is intended to be used to convert test
equipment from hi-impedence input to 50 ohms. It is labled 50 ohms and
measures 50 ohms with my DMM. It should be purely resistive and I do not
have any equipment to prove that it is.
The need to load it properly using the KAT2 was only because I wanted the
KAT2 in-circuit for improved forward power measurement within the K2. I
knew that it would need to load things to cancel itself out.
Based upon what Ron, Don and Jack have said, I guess that I should remove
the KAT2 and RF probe and try something similar to what I tried last time I
attempted to understand how well this radio tracks against the published
specifications.
Would it be reasonable to just place a short piece of coax between the load
and an O'Scope, measure the peak-to-peak voltage, divide by 2*SQRT(2) and go
from there?
Would this require knowing the coax velocity factor and dealing with prioper
lengths of coax based upon wavelength (half or quarter) at the different
frequencies?
I ask these questions because last time I tried using my Scope to make these
measurements, the measurements were obviously incorrect because they
indicated that my rig was way more than 100% efficient.
What I expect is that I can make apropriate measurements at 3 points on each
band and see that I get no more that 10% variation across said band and from
band-to-band. I expect that I have a problem on 10 Meters because I am
getting a HiCur indication at 3 amps when set for 10 watts, so something
needs changing there. However, until I have trustable measurements on the
other bands, I expect that untangling the issues will be impossible.
Help from the experts is needed on how to make such measurements without
fancy RF power meters. Obviously a purely resistive 50 ohm load is the
first requirement, and I believe that I have that.
73,
Fran
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