On Thu, 27 Mar 1997 10:11:50 -0600 Ed Jensen <ejensen@nmsu.edu> writes:
I plan to replace my TH3x this summer with a beam that uses
>full size
>elements. If anyone has first hand info on the little Tennadyne( LP5
>I
>think) or the C3S (I'm limited in the size of the antenna I can put on
>my
>tower), I would like to hear it.
>Ed Jensen, K5ED
>ae110@rgfn.epcc.edu or ejensen@nmsu.edu
The Force12 C3S looks like one of the best buys for
coverage/gain/size/price (IMHO). (Great for portable/DXpedition use!)
A two element Yagi, optimized for gain, peaks at close to 7.0 dBi in free
space. Improving F/B ratio will lower the gain to 6.0 to 6.5 dBi. A
short boom (0.2 - 0.3 Wavelength) 3 element Yagi can provide 7.5 dBi.
Going to .35 WL with 3 or 4 elements can produce 8.5 dBi.
Internacing reflectors works because the high frequency reflectors
are practically invisible to the lower frequencies and the low frequency
reflectors are BEHIND the high frequency reflectors.
You will notice that no commercial antennas use single monoband
directors. The reason for this is that on the higher frequencies, the
lower frequency directors will act as inefficient REFLECTORS placed
IN FRONT of the high frequency director. This is why Force 12 places
the higher frequency elements in front of the lower frequency elements
on their long boom multi-element antennas.
The full size 2 element Yagi gives good gain and bandwidth on a short
boom with a small turning radius and light weight. It is definitely a
reasonable option vs. the short boom 3 element tribanders. The 3 element
tribanders will probably have better Front/Back ratio, but,
as a contester, I find this to be an overrated feature...I LIKE hearing
DX (multipliers) off the back of my antenna!
A 2 element QUAD is also a good lightweight/small radius antenna.
Properly tuned, it should yield gains around 7.5 dBi in free space. Of
course it is more cumbersome and requires strong spreaders if
icing is a problem.
To obtain good gain with Log Periodic antennas, one must use a slow
taper and long booms. I would expect that 2 element monobanders would
yield more gain than a very short boom LPA.
de Tom N4KG
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