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Old October 4th 12, 12:56 AM posted to rec.radio.amateur.homebrew
Ralph Mowery Ralph Mowery is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 702
Default Modifying an SWR meter


"joseph2010" wrote in message
...
Ralph, Thanks for your informative reply. You're right, there were
several manufacturers that made these units (Midland, Pace, Numark,
etc.). I did try to hook it up, but the SWR was 1.3:1 (almost the same
as I got with a dummy load), which I thought was too good to be true,
but maybe it was due to the low wattage being used (4 watts). I'll get
some proper cables built and go from there. Thanks again.



If you can get two 50 ohm dummy loads you can put them into a T connector
and the swr should be around 2:1. That is one way to run a quick check.

Some times using low power will cause the swr to show differant as the
diodes will not have enough voltage to act the same as they do with a higher
voltage. That is called the square law reagon. While the readings may not
be accurate, the lower the reverse reading, the better.

I should qualify that statement about the SWR. The actual SWR will be the
same nomater what power you use, but some meters will show a differant
ammount due to the way the diodes act.

Depending on the antenna and the ammount of coax, the swr can be shown as
very low. If you have around 100 feet of rg58, the swr the meter shows will
be very low and not too much you do at the antenna will change it.
I made that mistake about 40 years ago when I built a 2 meter antenna and
fed it with 100 feet of rg-8. The swr was about 3:1 and nothing I did would
change it. Turns out that the center wire was not hooked to the antenna.
The coax has enough loss that it will only show about 3:1 with nothing
connected to it at 2 meters.