[TowerTalk] stacking distances -- YT and TA

[Tonno Vahk]

TA anyway does more accurate job.

I did the same with 4el 20m yagis.

50 and 100 is 16.2 dbi (about 2.4 dbi over single upper), 50 and 60 feet is
basically the same as the upper (13.5 dbi) so no gain really. 50 and 80 feet
is 15.3 dbi (about 1.6 dbi over the upper) so quite logical.

Keeping the upper beam fixed at 100 feet TA suggests around 60 feet height
for the lower.

Checked for 6el KLM (58') and 100 and 55 seemed best while you can improve
pattern in expense of some tenths of a db by rising it to 60 feet also.

But I guess it far less trustworthy in this respect than AO also results are
similar.

73
tonno
es5tv
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <towertalk@contesting.com>
Sent: Tuesday, January 08, 2002 3:03 PM
Subject: Re: [TowerTalk] stacking distances -- YT and TA


>
> At 01:23 AM 1/8/02 -0500, Tom Rauch wrote:
> >
> >> You have to be careful with YT, using stacks with close spacing.
> >> If you plot a stack of two antennas even one foot apart,
> >> YT will still show a 3 dB gain over a single antenna.
> >
> >Very interesting. It is amazing what is in those manuals
> >that I, like most people, never bother reading.
> >
> >Anyway, that's why I like the new Eznec with it's average gain! You
> >can look to see if average gain exceeds 0dB as an automatic red
> >flag.
>
> I think Dave's statement could be misread to mean that YT adds 3 dB gain
> for a stack over a single antenna, regardless of spacing.  It doesn't.
> Instead, there is a gain error that gets more obvious (larger and less
> consistent with NEC-2 models) as stack spacing is brought closer.
>
> What the YT manual says is "The internal Yagi model in YT is simple and
> does not compute interactions between individual Yagis in a stack -- YT
> assumes that each antenna is a point source. For antennas stacked more
than
> about a half wavelength apart this is not a problem. For example, you
> should be cautious specifying spacings less than about 20 feet on 20
meters
> (and proportionately scaled on other bands) because of mutual-coupling
> effects between real antennas."
>
> I verified this just now with the classic 2-high 4-element 20m yagi stack.
> At 50 and 100 ft, the stack's gain is given as 16.2 dBi, with the stack
> 2-2.2 dB better at peak than either individual antenna.  However, with the
> stack at 50 and 60 feet, the peak gain rises to 17.0 dBi, with the
> individual antennas 2.8 to 3.2 dB below that.  At intermediate spacings
> from 20 to 40 feet, the computed gain of the stack is consistently above
> that at 50 foot spacing.  This looks nothing like the curve of gain versus
> spacing produced by NEC-2 modeling.
>
> In the documentation, Dean recommends that YT be used for what it is good
> for, which is assessing the pattern effects of irregular terrain, and that
> "I would trust the results within plus/minus 3 dB."
>
> Does anyone know whether K6STI's TA, which uses NEC antenna models, does a
> more accurate job of predicting stack gain over terrain?
>
> 73, Pete N4ZR
>
> The revised World Contest
> Station Database
> is online at www.pvrc.org
>
>
>
>
>
> ________________________________________________________________________
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________________________________________________________________________
This list is sponsored by the new eHam.net Store.  When you buy products
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price goes to support this list.  Check it out at http://www.eham.net.

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