[TowerTalk] Force12 EF-320

[Jim Thomson]

Message: 6
Date: Mon, 8 Aug 2016 07:53:13 -0400
From: "john at kk9a.com" <john at kk9a.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Force12 EF-320

I have no experience with Force12 beams. However, since your post was
unanswered and lost in the measuring coax loss within .001dB thread I will
try to help. I believe that Force12 monobanders are OWA design, meaning
that the coax is directly connected to the driven element with no matching
to go wrong.  How high is the SWR and how are you measuring this?  If you
have coax in multiples of 1/2 WL lengths you can also check the impedance
with an antenna analyzer. Did you double check your measurements? Are you
using the Force12 balun and good coax? Is there anything near the antenna
that could be detuning it?

John KK9A

##  Only very few of the F12 monobanders use the OWA  direct 50 ohm feed, like their 
615 / 715 / 620 / 810 etc.  The rest all use a hairpin.   My bet he has an open braid somewhere which
will show up as a high swr.   Since he has a simple 3 el 20m yagi, the DE  will be either right at the top of the
tower, or next to the mast.   IE: the DE is easy to get to.    There is nothing to go wrong with the F12 hairpin
matching setups..... they are just a loop of  .375 OD  al soft drawn  3003 alloy, with the ends flattened. 

##  If you can still hear signals and band noise..and  swr is high,  its very likely you have continuity on the center
conductor..and the braid  / shielded side has gone open.    Which could be the coax connector and  /or balun. 

##  the hairpin will DC short the DE.   He should be able to put an ohm meter across the coax in the shack, and see
very low loop  resistance.  If it reads wide open, he has an open braid.    IF the DE is easy to get to, just stuff the MFJ-259
etc, right into the DE..via the balun....and then measure the SWR  vs freq across 20m.  

Jim  VE7RF