[Towertalk] Force 12 needs to do more homework

Bob Henderson bob@cytanet.com.cy
Sat, 11 May 2002 07:14:41 -0000

I don't agree!

The C31XR is a fine antenna.  Interlacing three full size separate feed
monoband yagis on a common boom is not a trivial thing.  Is there another
manufacturer who offers this?

My C31XR out of the box had a better than 1.8:1 SWR across all three bands
installed in separate feeder mode.  No parts were missing except for the
extension tips for 20m needed with 3 feeders and the wire for the additional

The antenna worked well without adjustment but the minimum SWR point was
above 1:1.  Mostly around 1.4:1.  Adjustment of the hairpins brought the
minimum SWR down close to 1:1 but took time.

Why did I bother?  Well I have a lot of filtering in my SO2R set-up which is
50 ohm stuff.  It works a whole lot better if the antenna feed impedance is
50 ohms too.  Also the Alpha 87A doesn't much like high SWR and I'd rather
it didn't trip out too often.

My only criticism of Force 12 comes from reading one other recent posting
where apparently Force 12 have stated they ship two separate models of the
C31XR, one for single feeder and the other for 3 feeders.  That's
crazy........the only extra things needed for 3 feeder implementation rather
than single feeder are two bits of ally tubing a few inches long and a piece
of wire a couple of feet long for the additional hairpin.  These should be
included with every C31XR in a bag marked "3-feeder installation kit".
Shouldn't cost you more than 50 cents to do that.

It's already been said, but I too have had antennas that go together in no
time and have a flat SWR across the band. They worked just great as dummy
loads!  The C31XR is not one of those!  I have used a whole range of
tribanders over the years and without question the C31XR is the best yet.
Just now I think I am going to stack three of them on a rotating 120ft
tower.  That's unless I opt for  something bigger.....maybe C49XRs!

I'm a fan of Force 12!  I have no commercial interest in them other than as
a very satisfied customer.

Long may they continue to innovate and prosper as a result!


Bob Henderson
5V7ZM, 9G5ZM, C21ZM, ZD9ZM

----- Original Message -----
From: <RLVZ@aol.com>
To: <towertalk@contesting.com>
Sent: Thursday, May 09, 2002 1:03 PM
Subject: [Towertalk] Force 12 needs to do more homework

> Force 12 needs to do more homework.  It should not be necessary for the
> consumer to have to do all this work (take the antenna down and modify it
> several times) to make a mass produced factory built F12 work properly.
> Richard- K9OM
> Dink
> I have a C31XR up at about 70 ft fed with three seperate feeders.  Each
> antenna is fed with 50m of HD100 coax and each has a choke balun of 12
> of coax with a piece of 6 inch dia plastic water pipe as a former so the
> turns don't bunch up.
> SWR on all bands is at 1.1:1 or better at my chosen centre frequency.
> are 14100, 21200, and 28200.  These c/f give me good swr across CW and
> sideband segments.  To achieve this I removed the tips from the 15m
> element,added extra length to the 20m element and used hairpin matches on
> all three driven elements.  These took some fiddling with to achieve best
> effect.
> The above swr readings were taken with the feeders to the other two yagis
> open circuit.  Any kind of load placed across the 20m coax whilst using
> messes up the SWR on 15m.  This has caused me a problem in my SO2R set-up
> which I have worked around by putting a 15m parallel tuned circuit in
> with the 20m feed.  I used a small L and big C to minimise the effect on
> 20m SWR.  It's a compromise but it does work.
> With good choke baluns on each driven element I have found SWR to be
> substantially independent of feeder length.  That is with 50m and longer
> feeder I haven't tried with feeders shorter than 50 metres.
> BTW You did remove the tips from the 15m elements didn't you?  The 15m
> elements as delivered are too long for the separate feeders option.
> I have added a Cushcraft XM240 at about 85 feet (turned 90 degrees to the
> C31XR) and I have inverted vee dipoles for 160m and 80m hung just below
> C31XR.  None of this seems to have had a materially adverse effect on swr
> performance of the C31XR so far as I have been able to judge.
> I hope this helps.
> 73
> Bob 5B4AGN
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