[TenTec] Model 238C Tuner Questions

Jim GM jim.gmforum at gmail.com
Wed Oct 17 12:27:01 EDT 2012

Hi Jimmy B.

I have been doing some measurements with My bird Watt meter. 50 ohm match
through a 1:2 balun.  Input impedance to inverted L is 25 ohms. SWR is
about 1.3:1 however Forward power 200 watts with Reflected power of 80
watts.  Feed line from balun to shack is 25 feet. Reflected power just gets
worse on other bands.  Lots and lots of common mode currents.  Too much for
just some balun to absorb that much RF.

So from what I have seen is that SWR is one animal and forward and
reflected power is another animal that needs to be dealt with.

This type of flow is just a waste, I read up on FCP single redial for a
single band seams to work just fine.  Multi band an antenna just creates
all sorts of common mode currents. Not Good. Causes all sorts of problems.

What I am trying to shoot for is some antenna with very low return RF. That
would mean that ether ground or the antenna is radiating all or most of the
energy put into it. a 50 50 chance on getting it right. A small florescent
tube, or NEON light taped on the wires will tell the story.

DX Engineering has those clamp on cores for common mode currents seam to
work well on the residual RF coming back but only after the Hi Reflected
power coming back is taken care of.
Jim B K9TF

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