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Old May 4th 05, 04:07 PM
Cecil Moore
 
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John Smith wrote:
It seems to work, all I have is another SWR with analog meter I constructed
myself to compare it with, soon as I locate someone with a commercial
meter--I will compare both of mine to it... Only real apparent problem is
the REF led changes brightness slowly (and here it is hard to "judge" SWR by
brilliance), until right at, or near, match, when it will plunge to darkness
rather quickly...


You are not reading SWR. All you are reading is net current.
Both LEDs have the same rectified net current through them.

Well, show me what is wrong and suggest an alternative circuit or mods to
set it proper (or explain in text, I will see how good I am at word problems
here)--I am all EARS Cecil... smile


Here's the last one I looked at:

http://www.mfjenterprises.com/man/pdf/MFJ-974H.pdf

You'll recognize the SWR circuitry at the input connector. Note
the capacitive dividers. That's what your circuit is missing.
Nowhere does your circuit sample the RF voltage.

This type of SWR meter samples the RF voltage (using a capacitive
divider) as one parameter. It samples the RF current (using the
toroid) as the other parameter. The two parameters are added before
rectification to obtain the forward power. The two parameters are
subtracted before rectification to obtain the reflected power. The
phasor addition and subtraction must be done before rectification.
--
73, Cecil http://www.qsl.net/w5dxp

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