[TowerTalk] Tribander question

[n4kg@juno.com]

The TH3 has a 14 ft boom which is only 0.2 WL on 20M,
0.3 WL on 15M, and 0.4 WL on 10M.  The maximum 
gain for a FULL SIZE 3L20 on a 0.2 WL boom is close
to 7.0 dBi which is also the maximum gain for a 2L on
a 0.15 WL boom.  Estimated trap losses are 0.5 dB.

The main shortcoming of the TH3 is limited bandwidth.
It seems to do a good job in the portion of the band
for which it is tuned but my experience is that gain
(competitiveness) seems to drop off on the other end 
of the band.

The C3 is essentially 2 full size elements on each band.
On 10M the parasitic element is a DIRECTOR with
NO reflector.  Personally, I prefer the C3S design
which utilizes 3 parasitic REFLECTORS on a shorter
boom or the C3E which adds a 10M reflector, making 
it 3 elements on 10M for improved gain and F/B.

Another option is a triband (or 5 band) 2L Quad.
Quads utilize full size wire elements which provide
good gain-bandwidth.  Newer designs with heavy
duty spreaders seem to hold up under icing better
than older designs.  There are at least 2 single feedline
Quads available on the market.  I believe W4RNL has 
details of a 5 band design on his WEB page that utilizes
separate feedlines which may be a better choice.

de  Tom  N4KG

On Tue, 6 Feb 2001  "Mike K9MI" <mdbrown@iquest.net> writes:
> This is a "what if" question, as I don't have
> the funds to do this right now anyway. But,
> maybe sometime in 2001...
> 
> Right now, I'm using at TH3 tribander at 40 feet.
> 
> Has anyone replaced a similar antenna (3 el trapped
> tribander w/ 14ft boom) with a Force 12 C3 ?  I'm
> relatively certain, that yes the C3 is better. But
> how much better ? 
> 
> Mike, K9MI
> 

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