[TowerTalk] Cable mismatches and swr

[Robert Shohet]

Hi Guys,

Here is a question on calculating cable mismatches and swr...

I have a 4sq fed by OLD RG8X to a WX0B stackmatch that my other 40 meter
antennas plug into.  The stackmatch is then fed with RG8X and run to the
shack.  (Yes, I KNOW that I should not be using RG8X much less old RG8X.).
The cable then goes into a T-connector with a 75 ohm CATV stub, and to the
radio.

For purposes of this question, forget the stub.

I want to replace the RG8X with 75 ohm CATV hardline which will have RG213
(50 ohm) pigtails at either end of the 4sq feedline and the stackmatch
feedline.

My question is as follows:

Normally when you run 50 ohm into 75 cable you introduce a mismatch which
should raise a flat swr to about 1.4 :1.
If I am using a 50 ohm pigtail from the 4 square to 75 ohm hardline and then
back to a 50 ohm cable to the stackmatch then hardline from the stackmatch
and then back to 50 ohm cable to the stub/shack, is the net effect 0 and the
swr should be unchanged?  Or will the swr balloon higher by the sum of ALL
the mismatches?

Your thoughts please!

Tnx & 73.

Bob KQ2M




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