Hi all,
A few questions:
1. I'm not disputing the quality of the Optibeam, but for comparisons, a JK
Tribander, at least when details were last available on the JK site, was
less than $1k. It looks built like the proverbial brick you-know-what, has
two elements on 20 and 15 and four on 10. The OB-7-3 is about $1,200
(according to the estimator formula at Array Solutions), has two elements on
20 and 15 and three on 10.
Is it really $200 better than a JK? For about the same money as the OB-7-3,
from JK you can get the Navassa5 and add gain on 17 and 12. For an extra
$80, you can add a two-element 6m to the Navassa5.
2. The Navassa5 is about $1,200 with 6m added. The F12 XR6 (same band
coverage, same element count) is $1,695. Is the XR6 really $400 better? The
folks with JK antennas rave about the build quality, so, is the latest
incarnation of F12 THAT much better at using NEC4 than W3JK?
I'm not criticizing anything. Just pointing out some facts and asking
questions.
73, kelly
ve4xt
On 4/7/15 9:23 AM, "Paul Christensen" <w9ac@arrl.net> wrote:
> The gain of a LPDA should be mostly consistent across its designed frequency
> of operation. If it's not, then there's a design error. So, I would
> expect one gain figure +/- some amount of variation in dB across the design
> spectrum.
>
> Assuming L.B. Cebik's set of LPDA formulas are more accurate than what had
> been used between 1960-2000, then this on-line calculator may be of
> interest:
>
> http://hamwaves.com/lpda/en/
>
> I recently purchased a Tennadyne T14-HD. It was not purchased for its
> published gain figure. Run through Cebik's formula and to achieve 8.5 dBd
> (or 10.65 dBi) in free space from 30m-10m, you'll see a surprising result
> when using optimum sigma and tau values.
>
> If the AutoEZ interface to EZNec can easily generate an accurate LPDA model,
> it would be worth validating against Cebik's work, although I have to
> believe he cross-checked his own math with NEC since he was well known for
> his NEC analysis.
>
> Paul, W9AC
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> jcjacobsen@q.com
> Sent: Tuesday, April 7, 2015 8:43 AM
> To: jim@audiosystemsgroup.com
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] Antenna choices
>
> Interesting topic. Jim was questioning the data on the Tennadyne LPDA
> products.
> <snip>
>
> 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. <<<<<<<<<
>
>
> <done>
>
>
> At the very bottom of the page for Original Tennadyne products is this
> statement:
>
>
> " *These gain figures are fictitious, but since other antenna manufacturers
> tend to use them to manipulate things in their favor by enhancing their
> specifications with phony data, we've added them so that you can get
> accurate comparisons. "
>
>
> I have no connection with Tennadynne or any other antenna manufacturer.
>
>
> 73
> K9WN Jake
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