I have one concern about adding much of a mast to the setup - even
when cranked down, the mast will add to the overturning moment, reducing
the structural capacity below what the manufacturer claims.
As for antennas, I vote for the KT34XA over the C4XL, for the following
reasons (excerpted from earlier posting):
You are on the distribution list because you replied to an earlier
posting of mine about the Force12 C4XL antennas. I have come to a
final conclusion regarding this subject, and thought you might be
interested in what I ultimately decided....
I currently have a KT-34XA at 70 feet, and a 40-2CD at 80 feet, on the same
mast. Of course what I'd REALLY like to do is put another 10 sections
of Rohn 45 under them! But my next tower project starts at the real estate
I have observed that height makes a BIG difference; and I'd like to get
the 20-10 antenna up that last 10 feet in anticipation of the next
time 10 and 15 open again. The thought has crossed my mind of replacing
both antennas with a Force 12 C4, which would cover 10-40 meters, and
have the advantage of all cohabitating at the same height on the mast.
If anyone out there has any experience with this antenna, I'd be
interested in hearing about it. Particularly, how does it compare to
my existing antennae in performance and windloading. I've heard lots
of good things about other Force 12 antennas (the C3 in particular).
I also wonder if the C4 has separate feedlines for 40 meters, and if both
antennas could be used at the same time without impossible interference
problems due to proximity of driven elements.
The above background was in my original posting. After talking to the
folks from Force12 at Dayton, and without really a lot of meaningful
consideration, I placed an order for the C4-XL at the Dayton special
price. Fortunately there was a three week lead time before the order
shipped, during which I had an opportunity to do LOTS of research
which ultimately led me to cancel the order. Please understand
that my ultimate conclusion was NOT that the C4-XL was a bad antenna;
I think it is a good antenna, it's just that I concluded that what
I had was already better... Here's my thoughts:
I have done a lot of modelling on mono-band models of the
KT-34XA (my existing antenna on 20-10), and I have modelled the C3.
My conclusion is that the C3 just cannot compete with the XA in the
forward gain department. Here are my observations:
1. Force12 C3 series antennas are well-built, using many desirable and
advanced construction techniques. Specificly rivets, and their mast-element
and mast-boom connections look really nice to me.
2. Force12 C3 series antennas are full-size, no loading 2-element beams
on 10-20. This means they can't be beat for efficiency.
3. As far as Force12 advertising claims, I'm skeptical. First, comparing
a C3 to a KT34XA, the XA is really 4 elements on 15 and 20, and 5-6 elements
on 20. If you check with the experts, or do some modelling, you'll
find that the XA comes out 4-8 dB better in the forward gain department.
4 dB is 60% of the power. To equate the two antennas' performance would
require that the XA dissipate almost 1KW in the form of heat. That would
be 100 watts per trap (there are 10 traps in an XA). I think that much power
would be enough to melt the plastic end caps out of the traps.
The traps of the XA are made out of three materials - air, aluminum,
and polyethylene (?) capacitor caps. Air is very low loss, the aluminum
tubing is of reasonable diameter so skin effect losses are minimal, and
the capacitor end caps constitute such a minute percentage of the capacitors
that they can't dissipate 100 watts each. The
upshot is that while there is merit in the efficiency arguement, there
isn't 4 dB of merit. I'd be willing to accept that antennas with lumped
traps like a TH7 or A4 etc would have higher losses. But the XA uses
linear loading and air-capacitors - you can't get much lower loss than that.
4. Consider this - a 2-element quad would have about one dB more gain
than a two-element yagi (such as a C3). A 2-element quad would also
be at least as efficient as a C3, if not more efficient, because of the
higher radiation resistance. I've had a 2-element quad up at the same
time as the XA, and while it comes close, the XA beats it 99% of the time
-usually by about 6 dB.
5. Force12 is very careful about making their most dramatic statement
always appear as a customer quote - they never directly state the following
as their own claim:
"The C3 outperforms every trapped tribander, regardless of boom length"
(quote may not be exact).
6. Force12 claims that all 7 elements are active on all bands. If this
means that the current flow in an element is non-zero, I guess they
are technically correct. If it means that the other elements contribute
significantly to gain or F/B, I disagree. I modelled the C3 on 20
meters, and got reasonably close numbers for gain and F/B to their
specs. Then I removed all the 10 and 15 meter elements. The pattern
change was really slight. Much less than .5 dB.
My conclusion was that the C3 antennas are really nice, well engineered,
well-built 2-element beams. They'd be a great replacement for a TH-32,
or even an A3 (if you buy the efficiency arguement). But they will not
provide the forward gain of an antenna with truly active elements on
a boom almost twice as long. And they won't beat a 2 element quad, either.
As far as comparisons between the 2-element 40 of the C4-XL versus
the 40-2CD, the 40-2CD has much wider bandwidth (250 kHz vs 130 kHz)
and has a longer boom length. The arguement would be between linear
loading on the Force12 versus the coils on a Cushcraft. W6QHS published
measured data for the coils on the 40-2CD - 12.93uH and a Q of 161!
That's pretty high Q. And if Force12 argues that linear loading is better
than coils for a 40 meter antenna, the same argument should hold
when comparing a linear laoded XA on 20 versus a TH7.
I called and cancelled my order for the C-4XL. I'm going to work
this summer to swap the 40-2CD at 80 feet with the KT-34XA at 70 feet.
The 40-2CD will do nearly as well at the lower height, and the XA will
benefit 3 bands (if they ever open again!) with the added
10 feet of height.
In the course of this investigation, I obtained a model for the 40-2CD;
I generated a model for the C3 (from owner's manual measurements); and
I have generated 3 mono-band models for the KT-34XA at 10, 15, and 20
-Tony, K1KP, firstname.lastname@example.org