[TowerTalk] Force 12 C3S Experience

Greg Clark g.w.clark@cummins.com
Thu, 05 Nov 1998 11:28:11 -0500

Well, it's my turn to let you in on some of my Force 12 C3S experiences.

I purchased 2 C3S's almost 18 or 19 months ago.  They've been in the
barn until time and money allowed me to do some work with them.  The
idea was to have 2 of them in a stack configuration for my second radio.

Well, I still don't have alot of time or money, so my goal has been to
get one of the antennas on a side-mount dedicated to radio #2.  I
started working on the antenna on a Sunday and have been doing part-time
work on it from that point.  It has taken about 3 hours total to


- No major ones, but I was starting to worry.  The first element
assembled needed to have six rivet holes re-drilled.  This number
decreased for each element thereafter until I got to an element that
needed no drilling..yea.

- Tuning...what a pain in the rear..at least for 10m.  I've seen similar
comments from others and I can tell you "I feel your pain".

My tuning setup consists of about 40ft of RG-213...not the 100ft as
defined in the manual.  I then connect an Autek RF-1 antenna analyzer to
one end of the 213 and the other is feeding a new W2AU beam balun.  To
tune the antenna off of the tower, I hoist the antenna between my 2
towers so that it is pointing straight up with the reflector about 6
feet off of the ground.  

Out of the Box - Per the manual SWR points are as follows:

20m (final)

1.5 - 14.0
1.2 - 14.1
1.0 - 14.2
1.3 - 14.3


2.9 - 21.0
2.2 - 21.1
1.6 - 21.2
1.1 - 21.3
1.3 - 21.4


7.5 - 28.0
6.6 - 28.2
5.5 - 28.4
4.4 - 28.6
3.2 - 28.8
1.0 - 29.33 - Kinda high in the band huh?

Well, per the manual, I was able to lengthen the 15m element and ended
up with a curve that I was happy with.  Here is it's final plot.

15m final

1.8 - 21.0
1.4 - 21.1
1.6 - 21.2
2.2 - 21.3
3.0 - 21.4

On 10m I was in a pinch.  On one of the 10m elements, there were only 3
rivet holes to extend the element, on the other 10m element there were
4.  Even when I extended the element tips to their maximum, the resonant
point on 10 was up at 28.600.

So, due to me running out of element tip to lengthen, I then went to the
next section of the element toward the boom to look for some extra
length.  I did this on both 10m elements.  This was not a quick and
simple process.  I finally ended up with the following curve for 10m.

10m final

2.2 - 28.0
1.4 - 28.2
1.7 - 28.4
2.9 - 28.6
4.3 - 28.8

It ain't great but it's better that what I started with.

>From the time I hoisted the antenna up the first time to the last time
that I sat it back on the ground was 2 hours 50 minutes.  The majority
of that time was jerking around with the 10m settings and then
re-engineering it in the field (drill rivets/drill new holes/pop
rivets...measure..etc).  This was not fun.  Thank goodness it's not a
big antenna but it was still a pain and to boot it was about 30 deg F
all the time.

I have another one of these to put up...probably next Summer, but at
least I will have my notes to get me through that assembly and tuning

I don't have the antenna on the tower yet.  I hope to have it in place
for SS this weekend.  I'll let you know how it performs, but I did want
those that have the C3S and have had problems on 10m to know that there
is a way to make it work.  I, like other TT posters wonder why the
antenna was designed for such a high 10m resonant frequency of 28.800. 
Why not ship it with about 4 more inches of length in the 10m elements
to save the majority of the users the above described procedure?

Hope this helps someone out there.


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