N4KG comments follow questions and first response.
On Sun, 18 Oct 1998 22:38:06 -0400 "DavidC" <davidc@bit-net.com> writes:
>
>> > I guess my question is -- Does anyone with real experience with
>these
>antennas
>> > have any reason one should buy a C3S instead of a full size C3
>(except the
>> > slightly narrower 10M bandwith) ?? Swilsonac6@aol.com
>> For all intents and purposes, it's the same antenna but with less
>> turning radius. The C-3SS was the result of trying to shrink the
>C-3.
>They all work FB.
>> Cheers, Steve K7LXC
>
>I was just convinced to pass on a nice used C3S because I was told by
>my
>Elmer that boom length is critical to gain and the C3S is way too
>short to
>claim gain close to the C3 ... I suppose this will stir up some sort
>of
>hornet's nest about the boom length issue ... go for it, as always it
>is
>certain to be a wonderful education ... and I will shut up and just
>read.
> 73, DavidC AA1FA
/////////////////////////////////////
This is a case where a little knowledge is dangerous.
Both the C3 and C3S act as 2 element Yagi's on each band
and therefore have very similar gain figures.
The C3 uses two driven elements for greater SWR bandwidth
and it uses a parasitic DIRECTOR on 10M, placed out in front
of the rest of the antenna, accounting for the extra boom length.
(Yes, a 10M REFLECTOR could be added for extra gain on 10M).
On 15 and 20 M, it uses parasitic REFLECTORS, no directors.
The C3S uses a single driven element on 10M and parasitic
REFLECTORS on all three bands.
Parasitic REFLECTORS can be lined up with little or no degradation
since the highest frequency sees the closest reflector. Shorter elements
are nearly invisible to lower frequencies which accounts for the lack
of destructive interference.
Parasitic DIRECTORS in multi band antennas cause destructive
interference since a 20M director will act as an inefficient reflector
IN FRONT of the 15M elements. Likewise a 15M director will act
as an inefficient reflector IN FRONT of the 10M elements. These
interference problems are typically overcome by using traps to
break up the elements, using forward staggering, or the use of
lots of parasleeve elements on the higher bands around the
longer elements.
When comparing boom length of antennas, one must look at the
USEFUL boom length on a band by band basis. Don't get confused
by TOTAL boom length if active elements are not distributed over the
complete boom.
de Tom N4KG
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