[TowerTalk] Ladder Line Fed Dipole Issue

[Mike Fahmie]

Your transmission line, being an odd multiple of ¼ wavelength, will transform your nominal 70Ω antenna to about 1300Ω so your observed SWR seems to be what I would expect.  If the line were an even multiple, then 70Ω would be presented at the radio end with a 1.4:1 SWR into your 50Ω system.
-Mike-WA6ZTY

      From: Tony <dxdx at optonline.net>
 To: TowerTalk at contesting.com 
 Sent: Thursday, October 25, 2018 10:14 AM
 Subject: [TowerTalk] Ladder Line Fed Dipole Issue
   
All:

I have an 80 meter dipole fed with 300 ohm ladder line that needed to be 
moved to a different location. The antenna is 110 feet long and the 
ladder line is attached to a DX Engineering 1:1 tuner balun with a short 
10 foot run of coax. The length of the ladder line is cut to an odd 
multiple of the 80 meter wavelength.

The SWR on 80 meters was very high so I trimmed the ladder line a few 
inches which lowered it from 25:1 to 18:1. I continued to trim a few 
more inches and noticed no change: changing the coax length had no effect.

My question is: is it normal to expect an SWR to be that high on 80 
meters with this setup? Should I continue trimming the feed line to find 
a length that presents a more reasonable SWR or look for other issues 
with the antenna system? The ladder line does not touch the ground, it's 
not folded onto itself and it's not near any metal object.

Tony

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