[TowerTalk] Tribander losses

[Jason Hissong]

Please forgive me if my observation is not correct (and please correct me if
I am incorrect :) The TH7DXX is not that much better than the C3 according
to these results (and that probably was the point you were making there Pete
:).  The C3 is really three 2 element Yagis on one boom and the TH7DXX looks
to be a multielement tribander on one boom (with traps).

So from these results, it looks like the C3 is not performing as well as the
TH7DXX, but it is not far behind it.  From this, I would conclude that the
trapless design (and I have not bought a C3 yet to be a true supporter, but
I am leaning that way) is pretty efficient.  Is there any online reference
to the comparisons between different brands of Yagi antennas?  I have seen
references to someone's exhaustive testing in some posts.

Anyway, just some of my own naive observations :)

Thanks again for all of your responses to my earlier posts!!  They have
proven very helpful...  CyberElmers... neat...

73 de KC8HYI.

----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <towertalk@contesting.com>
Sent: Monday, July 17, 2000 9:07 PM
Subject: [TowerTalk] Tribander losses


>
> For whatever it may be worth, following data were developed using NEC-2
and
> carefully-converged models.  Interpretation is up to you guys:
>
> 1.  Following gain figures are for the Force 12 C-3.  Considering the very
> small currents flowing in any elements but the ones specifically designed
> for the band in use, I think it's fair to describe the C-3 as a 2-element
> yagi on each of the 3 bands 20-10, with effective boomlengths of 11 ft on
> 20, 8 ft on 15, and ~6 feet on 10.  Gain in free space was:
>
> 20  6.84 dBi
> 15  6.46
> 10  6.22
>
> Gain at 97 feet above normal ground was:
>
> 20 12.34 dBi
> 15 12.21 dBi
> 10 12.00 dBi
>
> Compare those numbers with the following, which reflect an idealized
> TH-7DXX model for each band.  The effective boom length is 24 feet, and
the
> antenna has 4 elements on 20 and 15, and 5 elements on 10.  In each case,
> elements 2 and 3 (from the back) are driven, with about 2 feet between
> them.  In each case, no traps are included -- in effect, each antenna
> represents the parts of the antenna that are "supposed" to be in use on a
> given band, with perfectly cylindrical elements.  In my view, this
probably
> represents the best performance achievable from the TH-7, given perfect
traps.
>
> Free space:
>
> 20 7.58 dBi
> 15 8.06
> 10 8.36
>
> 97 feet up:
>
> 20 13.11 dBi
> 15 13.74
> 10 14.14
>
> Note that the absolute differences between the two antennas remain very
> similar from the free space case to the above-ground one - about .75 dB on
> 20, 1.6 dB on 15, and 2.1 on 10.  My horseback guess is that these results
> show that the TH-7 is compromised toward 15 meter performance (a
reasonable
> thing to do), and that, in general, the results are not as good as one
> would expect from a 24-foot boom.
>
> Can anyone advise what gain should be expected from 3 monoband elements on
> a 24-foot boom on 20 and 15, or 4 elements on 10 (assuming reasonable SWR
> bandwidth and F/B performance across the band)?
>
> 73, Pete Smith N4ZR
>
> The World Contest Station Database
> is back up and running at
> http://www.qsl.net/n4zr
>
>
>
> --
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>


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