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Fwd: C-3 Info

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Subject: Fwd: C-3 Info
From: (
Date: Tue, 14 Jan 1997 14:22:05 -0500 (EST)
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Date: 97-01-14 13:45:05 EST

Steve - the following is the reply I sent to Mr. Soper, who asked about the
vs. the rest. Thought you might find it interesting. I am not sure if all my 
replies end up at everyone's Tower Reflector mailbox or not!

Hi, Pete.

Steve already mentioned in his reply that there is a detailed account of the 
basic design process of the C-3 contained in ARRAY OF LIGHT. So, not to 
re-write that section of the book, I'll only touch on a few important 

Firstly, all the elements in the C-3 are full size. There are no traps or 
loading coils in any elements from Force 12. If we thought traps of any 
kind (coil/can, KLM) were a valid method for providing performance antennas, 
we would have used them. We were starting with a clean slate. 

To be sure nobody nit-picks this, one place we do use small inductors 
(coils) is in the 80 and 160 mtr switch boxes, which are located at the 
center of the element(s). They are relay-switched and enable excursions 
within the band (cw to phone, plus sections within the cw and phone 
portions). These boxes are available for all three lengths (54, 68, 
84') 80/75 mtr dipoles and Yagis and the switch box is standard for the 
rotatable 160 mtr dipole. We also make a switch box for the 80/75 and 160 

The basic design goals for the C-3 (the name came later) were to provide a 
low profile, strong, light weight Yagi antenna for 20-15-10 with at least as 
much gain as trapped antennas. It also needed to have a single feedline. The 
process took 2 1/2 years. The easiest part was determining how much gain was 
needed. The most difficult was devloping the 3-band feed system, which 
actually turned out to excite the array on 5 bands (17 and 12).

The gain needed was variable. 20 mtrs was easily matched or exceeded by a 2 
element Yagi. Most (not all) trapped antennas were usually best on 15. 10 
mtrs had the best on the KT-34XA, which should not be a surprise. It has 
several full size elements (within the traps) on a fairly long boom. It has 
good gain on 10, but no where near the claims. Actually, nobody's claimed 
numbers for trapped antennas are close and you don't even need to measure 
them - just run some monoband Yagi models yourself. Better get back on 
the, it was decided to incorporate a trio of 2 element Yagis on 
the same boom in such a way that they would not destructively interact. In 
fact, they are arranged so that they enhance each other. All the elements 
carry current regardless of the frequency of excitation (20-10), so the 
question of "how many elements are active on a band" is not really relevant. 
That is a carry-over from an older generation. The real question is how much 
gain does it have?

The answer is simple - model it or test it - or both. Any way you like, the 
numbers are the same - nominally a good 2 elemenet Yagi...and...before 
someone is quick to say something like, "That can't possibly our perform my 
X-element tribander", let's recall how we got here. We tested the antennas 
first, remember?! It is not how many elements the antenna has, it is not 
necessarily how long the boom is (often appropriate, though), it is how 
efficient the antenna is. That word "efficient" is the key. What one should 
want is gain - real gain, not claimed numbers.

You can depend upon the Force 12 numbers. They have been modeled on NEC2, 
tested and validated, plus some have now been run on NEC4. Same results: 
accurate specs. Always have been. No other way to be as far as I'm 
concerned. By the way, we make over 120 antennas - from 160 mtrs to 6 GHz.  

Which triband antenna would I use? If my tower weren't so populated with 80 
mtr stuff, I would use the 33' boom 5BA (20-17-15-12-10), because I like 17 
mtrs. As it is, I use a C-3. If I want more gain, a simple stack of two of 
them spaced about 30' is a real winner.

I'll conclude with a short personal note (from me, not the company) to 
someone who thinks that chosing a C-3 over an "XA" would be smoking 
something, since I have done my fair share of contesting and DXpeditions:
        any day take a C-3 - smaller, lighter, less tower strain, no 500 
        parts to assemble and maintain, no power limit, maybe not always 
        through before an XA on 10 mtrs, but 20 is where the horses run.
        - other numbers might look good, but they are only numbers. 

Hope you enjoyed this, but the real purpose is to advance our knowledge of 
antennas. Part of that is realizing accurate specs exist at least in one 
place. Another part is perhaps, "unlearning" things we have collectively 
been "taught" through certain literature.

                73, Tom, N6BT
                Force 12 Antennas and Systems

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