[TowerTalk] Inverted L SWR High

[Dinsterdog@aol.com]

Jack-

Multimatch UNUN
model W2FMI- 1.78:1 HMMU50

My guess is that the impedence of the Inv L is much less than the 50 ohm coax 
causing a higher than expected SWR-  There is an easy fix- - I had the same 
problem.  I kept adding radials and my SWR kept increasing- As you add 
radials, you might notice your SWR goes up some more as the ground losses 
become minimized and the radio better sees the true impedence of the antenna-

 To match the Inv L to my 50 ohm coax, I used a Amidon UNUN (unbalanced to 
unbalanced transformer) It is really a sharp device-  you plug your coax on 
one side of this little box from the antenna and the feedline going into the 
shack on the other side-   Mine is at the base of the Inv L feedpoint- 
through a combination of plugs- you can match 50 ohm coax to a variety of 
possible impdedences of the Inv L- Once you find the right combo- your SWR 
will be very close to 1:1 at resonance- that is, if this is what the problem 
is about-  Before you buy an UNUN, you might want to disconnect your radials 
and check the SWR.  If it goes down, then you know this is what your problem 
is- When I first hooked up my Inv L, with one radial- I thought it was 
awesome my SWR was 1:1- Then W0YG told me I had a nicely tuned dummy load and 
suggested I add radials- when my SWR went up- I thought he was pulling one on 
me when he told me I was improving the antenna- Then I got an UNUN and the 
rest is history-  I now have 90 1/4 wave radials below the Inv L--  without 
the UNUN, I'm at 3:1......with the UNUN, I'm matched pretty well-

A lot of DXpeditions use UNUN's for wire antennas as they are never sure what 
to expect at times with antenna set ups etc...that is why I like the amidon 
UNUN because it can match a number of possible impedences.  Ruling out a lot 
of other possibilites- I'm sure an impedence mismatch is your problem-

The Amidon UNUN can match the following impedences to 50 ohms:

4.08 to 50 ohms
16.34 to 50
36.76 to 50
5.56 to 50
22.22 to 50
3.125 to 50
12.5 to 50 ohms      This is the one I use for the best match, almost 1:1 and 
gives me a 2:1 bandwidth from 1.808-1.853
28.13 to 50

You can reach Amidon at 714-850-4660 or I'm sure one of the tech heads on TT 
can tell you how to make one-  I like the commerical version as it comes in a 
decent water tight box and worked right out of the box-       

73  Paul  N0AH

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