[TowerTalk] Tower height increments

[Michael Tope]

During his talk at Visalia, I asked Dean, N6BV why his TOA statistics
showed that takeoff angles would be higher on 10 meters than 15 (he
was showing a case study comparing TOAs at W6NL and N6RO). That
didn't make sense to me (I would have expected the opposite) and
Dean didn't really have a good answer. Anyone have an explanation for
that?

Thanks,

Mike, W4EF.................................

----- Original Message -----
From: "Guy Olinger, K2AV" <olinger at bellsouth.net>
To: "Jim Lux" <jimlux at earthlink.net>; "W3YY" <w3yy at cox.net>; "TowerTalk
List" <towertalk at contesting.com>
Sent: Saturday, October 16, 2004 9:04 AM
Subject: Re: [TowerTalk] Tower height increments


>
> ----- Original Message -----
> From: "Jim Lux" <jimlux at earthlink.net>
>
>
> > and the peak elevation angle for propagation on 40 is only 3
> > degrees above the horizon
>
> While I agree with the admonition to consider the effects of tower
> height on the lower takeoff angles...
>
> It is neither proven nor universally accepted that on 40m the "best"
> or "peak" takeoff angle is three degrees for all amateur radio needs.
>
> That three degree figure probably comes from VOACAP or VOACAP derived
> sources. Those programs have an entirely different agenda that is only
> a portion of typical ham radio uses and needs. VOACAP has broadcast
> derived blind spots that have to be worked around carefully.
> Particularly, VOACAP heavily weights takeoff angles that are
> continuously successful over long times and calendar intervals. A one
> hour strong opening somewhere, that would be a ham's delight, is
> largely dunned by VOACAP.
>
> VOACAP assumes that a broadcaster can actually construct high, large
> and efficient enough antennas, and run high enough power levels to
> make use of such openings.
>
> The experience at large contest stations with switchable antennas
> confirms that higher angles, even in the 20's, are significant on 40m
> over the course of an evening, depending on conditions, path to DX and
> distance.
>
> It was discovered, only last year, that VOACAP systematically
> discarded any data regarding a fourth incoming angle, that combined
> with a low starting angle (such as one or three degrees), made it
> incapable of reporting the existence of significant high incoming
> angles. It is a restriction that can be removed by completely recoding
> the application and its spin-offs in something other than its
> sixties-based Fortran.
>
> A two element 40m beam at 70' will prove to be an excellent antenna if
> it's not lossy and the f/b is decent.
>
> Particularly if you mainly want to work DX, the 70' height provides a
> rejection of high angles (30 and up) and rejection of close in (NVIS)
> signals and QRN which can be extremely helpful.
>
> You may be beaten out by a 5 element wide spaced quad, but hey...
>
> 73, and good luck.
>
> Guy.
>
> _______________________________________________
>
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>
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