Two weeks ago I posted a query about problems I was having with narrow
bandwidth and frequency resonance problems with a newly erected C-3S from
Force 12. I am happy to report that the antenna is now working properly and
that the problem was not the antenna but two bad pieces of coax in the
shack. The saga of how the problem was trouble shot and my frustration with
getting technical help from the folks at Force 12 is carried below for
those of you who wrote me with other similar problems with this and other
Force 12 antennas. For those of you who are not interested in this lengthy
story time to <right click> and <delete message>.
The story starts a month ago. I received a new Force 12, C-3S direct from
the factory. The antenna went together quite easily. All 6 elements
assembled and in the air in 4 hours. For the uninitiated the Force 12
antennas use "pop" rivets to hold the element sections together, if drilled
properly at the factory (some folks have had problems in the past), this
ensures that the element lengths will be exactly as designed, actually
pretty fool proof. The biggest draw back is the necessity of drilling out
rivets to adjust the element tips if you have to adjust the resonant
frequency of the antenna later. I would recommend that you put the driven
element tips together DXpedition style (put the rivet in the hole but don't
"pop" it but rather hold it in with a wrap of black tape) , once the
antenna is dialed in you can "pop" the element tip rivets later. Assembled
per the manual the antenna resonates (per the manual) a little high in the
band for my taste (21.225 and 28.800). Depending on your operating habits
you might want to start with the 10 and 15 drivers a 1/2" longer than spec
if you are a cw type like myself.
As reported two weeks ago my antenna resisted having its frequency lowered
and the bandwidth was quite narrow, only 300 KHz on 15M and 400 KHz or so
on 10M. In all I made 7 phone calls, sent 3 FAX and 5 emails. In spite of a
note to the reflector by Force 12 about E-mail vs FAX recently, none of my
FAX were answered or acknowledged. One email was answered by someone named
Natan who asked some pertinent questions, but never replied again. Although
the literature refers to a direct dial number for "technical" inquiries.
They will take technical questions on the 800 number. I respected that the
800 number was for orders only for awhile but after the 4th phone call gave
up and started using the 800 number. For the first 5 phone calls Tom ( who
is apparently the only person qualified to answer technical questions a
Force 12) was either out of town, out of the country or just plain
unavailable. At phone call number 6 I was told that again Tom was not there
and would not be back for two weeks. At this point I told the young lady
that I wanted to return the antenna and get my money back. (whatever you do
don't call her "sweet heart" that really pisses her off even when done
nicely). She said no one had ever done that before (right ) and that I
would have to talk to her supervisor someone named Mary. I adamantly asked
her to have Mary call me with return instructions, after 4 hours no Mary. I
called the 7th time and asked to talk to Mary this time. Mary came on and
when I told her I wanted to return the antenna she promptly told me to hold
on a minute and magically Tom came on the line. After lecturing me about
calling his phone girl "sweet heart" we got down to the real problem.
First the element spacings on my antenna (the element brackets come
pre-riveted) were not exactly as per the manual by a couple of inches in
some cases. Also I was informed that while the drawing in the instructions
shows dimensions measured from element center to element center, that the
correct reference is the back of the element bracket. Tom also said that
the reflector to driven element spacing is not "real" critical, the element
spacing between the three driven elements is quite critical and these were
right on. Once we cleared up that the antenna appeared to be constructed
ok. The give away (for Tom) was not the VSWR on 10M and 15M but the fact
the 20M was too flat, less than 1.3:1 across the band. (Force 12 if your
reading this, it would help if you would publish SWR curves in the manual)
. Tom suspected bad coax or coupling into a nearby structure. Having
resolved that the dimensional problem was not a "real" problem, and having
the advantage of "seeing" the installation I was reasonably sure that
coupling was not the culprit. I then set out to check for bad coax which
turned out to be quite tricky as I have 5 different pieces of coax in this
line and two of them were bad!
the setup looks like this:
TS-850 -coax- TL-922 -coax- Tuner -coax- ant switch(in shack)
-300' coax- ant switch (remote) -coax- antenna.
The second clue is that the SWR bridge in the antenna tuner and the SWR
meter in the TS-850 gave significantly different SWR readings and the
frequency of minimum SWR was quite different between the two units which
are separated by almost 7' of coax. The third clue was that with a 50 ohm
dummy load out at the antenna I was getting a 1.5:1 SWR back in the shack.
By process of elimination removing the coax in the shack one by one I found
that the first piece of bad coax between the rig and the amp. I replaced it
with a more substantial piece of RG-213 put everything back together only
to find more flaky (but different) SWR readings. More measurements and
process of elimination revealed that the coax from the Amp to the Tuner was
flaky as well. Both of these pieces were only 3' long, made from RG8 with
that soft foam dielectric and had been in the shack for years. I can only
surmise that they were bent too tightly from a radius point view at
sometime and that the dielectric cold flowed, anyway guess they are no
longer 50 ohms. The SWR bridge in the tuner and the TS-850 agree quite
closely now, the bandwidth on 15M is 450Khz and 10M 850KHz (still a bit
high in the band though) . 20M SWR is 1.6:1 at the band edges and much
sharper than before.
The biggest clue here should have been the fact that the SWR was not the
same in both the rig and the antenna tuner seperated by a few feet of coax.
Both Tom and I missed this initially although Tom instictively suspected a
coax problem (although I think his money was on the 300' from the shack to
the barn) based on the 20M performance.
If you waded through all of this I hope this helps some of the rest of you
out there who wrote me that you were having related problems. The C-3S is a
nice little antenna with very good on the air performance. It is small and
light weight in general seems to get out as good as my old Cushcraft A4.
It doesnt have the front to back that my full sized A4 had but at almost
half the size and weight its a lot easier for a old man to throw around on
a tower. The lack of traps which were a maintenance and reliabilty problem
on the A4 is a plus as well. Not much can go wrong with the C-3S.In short
the C3S is hard to beat in its size and weight class, but God help you if
you need a question answered. Will I buy another Force 12 antenna? Maybe in
a couple of years after the drinking has killed a few more brain cells and
I've forgotten my current level of frustration. 3 FAX, 5 E-mails and 7
Phone calls is too much to ask.
Dave
K9NX
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