I can confirm all Greg has said about the C3S. I put a pair of these up last
year and found the same problem with 10m. I ended up extending the elements
with small pieces of spare tube I had around the shack. After getting the first
to play at the required frequency I had do then copy it to the second.
One other problem I have is the drastic swr changes that occur in windy
conditions. The swr is all over the place on 10 and 15 m when the wind gets
up, this causes major problems with my Alpha 87a which trips constantly
when the wind blows. My next task is to try to add some support to the
elements in the form of spacers to try to maintain equal spacing between them.
Has anyone else overcome this problem ?
With regard to performance the C3S is excellent as a single antenna however
I have never found the pair better than the single top. When switching between
top and the pair I have never been able to see any change to the signals on
TX or RX. These tests have been carried out over a long period on all bands
and conditions.
The beams are fed through a stackmatch with the top at 90ft and lower at
60ft I also have a 402-cd between them at 80ft.
Has anyone any suggestions on how I may get them to play as a stack ?
Jan
G0IVZ
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From: Greg Clark[SMTP:g.w.clark@cummins.com]
Sent: 05 November 1998 16:28
To: towertalk@contesting.com
Subject: [TowerTalk] Force 12 C3S Experience
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
assemble.
Problems
- 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
15m
2.9 - 21.0
2.2 - 21.1
1.6 - 21.2
1.1 - 21.3
1.3 - 21.4
10m
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
procedure.
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.
73/Greg
K9IG
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