Jim typed what I was thinking.
What is it that is gained by going to that particular Optibeam? You will lose
6m, as the T11 covers 6m. I don't think there is going to be a gain
improvement since that particular Optibeam has such short element spacing.
Unfortunately, the gain figures of all Tennadyne antennas are hopelessly
optimistic. I've modeled my T8 and it is a little less gain than a C3 (same
overall boom length of 18 ft on both).
The only way you're going to make a valid on the air comparison of both
antennas is to get them in the air at the same time at the same height where
you can A/B switch them and see. Sounds like an awful lot of expense and
hassle for no way of proving the results unless you have two towers.
One plug for Tennadyne: They are very inexpensive compared to most everything
else on the market today.
Chris
KF7P
On Apr 6, 2015, at 11:47 PM, Jim Brown wrote:
> On Mon,4/6/2015 8:14 PM, Matthew King - KK4CPS wrote:
>> What are you unhappy with about the T11, and what are you looking to
>> improve?
>
> Yes, that's the real question. Part of that is to know the forward gain of
> the T11. I see a single number for gain for an antenna that covers two
> octaves of frequency. Somehow I don't trust that number on all bands. Also,
> by the gain numbers (5.8 dBd, 7.94 dBi, 13.14 dBi @ 1 wavelength height) I
> see an asterisk, but no note to go with the asterisk. :) There's an LPDA
> design in the ARRL Handbook -- it's 12 elements on a 26 ft boom, 2 ft longer
> than the T11. It's gain is 6.6 - 6.9 dBi, which is 1 - 1.3 dB less than the
> gain claimed for the T11, so there's either some design magic or some
> specsmanship happening with the T11. :).
>
> Now, look at the Optibeam numbers and description. This is a 2-el Yagi on all
> bands except 10M and maybe 12M. The gain numbers are 4.3-4.5 dBd which
> translate to 6.45 - 6.65 dBi (free space). That's slightly better than a near
> perfect 2-el Yagi, so there's either some design magic or some specsmanship
> happening here too. :)
>
> Now look at the 3-el SteppIR -- 7.4 dBi on 20M, 8.3 dBi on 17, 8.5 on 15, 8.8
> on 12, 9 dBi on 10M, and 10.1 dBi on 6M (with 4th fixed element). Those
> numbers are quite believable for a 3-el monoband Yagi on an 18 ft boom. The
> gain is lower on 20M because the boom is a bit short for 20M, and the gain
> improves as the boom gets longer as a fraction of a wavelength.
>
> So -- repeating the question, what do you hope to achieve by going to another
> antenna? There seems to be no question that the Optibeam is ruggedly built,
> but it's unlikely that it will perform measurably better that what you have.
> Folks are always saying that whatever they have is wonderful, usually based
> on all the DX they worked. But the basic facts are that if you want more
> gain, you need more elements PER BAND and a longer boom, also between
> elements. For example -- with the Optibeam, there are two 20M elements and
> they appear from the photo to be only about 8 ft apart. That's awfully closed
> spaced for 20M -- the SteppIR has 3 el 8 ft apart, and that spacing is short
> for 20M.
>
> The OB 11-5 (3-el/band, 19 ft boom) looks to be the performance equivalent of
> the 3-el SteppIR, the 16-5 (4-el/band, 33 ft boom) the performance equivalent
> of the 4-el straight SteppIR. At the current EU-dollar value, the 11-5 is
> about $1,650, the 16-5 about $2,640. The SteppIRs are about $2,000 and $2,800
> respectively.
>
> 73, Jim K9YC
>
>
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