David, I have found that HFTA (with Microdem) works as advertised. The
program accurately predicted how my antenna installation would work by antenna
height band, by DX destination and azimuth based on my exact terrain.
In some ways it needs to stay simple so it can be somewhat user friendly. For
example the DX destinations are limited to almost entire continents and the
takeoff angles to Columbia would be very different compared to Tierra Del Fuego.
Given the need to keep the program simple I have been constantly amazed at how
well it modeled my system based on what I have since learned in practice. All
of its calclulations turned out to be very accurate.
Tribander at 43' with 4 el 6m yagi 7' higher at 50' -- base of tower at 225'
ASL on steep hill sloping East to San Diego Bay with a variety of hills and
canyons in the other directions then sloping off to the Pacific Ocean.
Needless to say my QTH was really fun to model and very educational.
Regards, John NA6L -
-----Original Message-----
From: David Gilbert <xdavid@cis-broadband.com>
To: towertalk <towertalk@contesting.com>
Sent: Fri, Mar 2, 2012 11:15 am
Subject: Re: [TowerTalk] 15 meter yagi height for 6000 miles
That says more about what some people read into computer programs than
it does about about "what some computer says is optimum". VOACAP is
based upon empirical data and statistical analysis, and as such it
displays predicted (not absolute) results for a representative (not
absolute) time period within certain accuracy limits . HFTA used VOACAP
to determine the predicted best takeoff angles for various paths **as an
average over an entire eleven year sunspot cycle**.
As a planning tool HFTA is the best we have to work with. It is based
upon sound science and was written by a competent software engineer.
It does pretty much exactly what it was intended to do ... give you the
best chance of optimizing your results over a long period of time.
Anybody who thinks that it will hold true in every instance, or that
actual results won't often be even better than predicted, doesn't
understand the tool that they are using or the physics behind it.
Dave AB7E
On 3/2/2012 10:39 AM, David Blake wrote:
>
> I have never had an tower higher than 48 feet yet somehow have managed to
> work
ALL DXCCs (#1 Honor Roll). and all 40 zones
> on 6 bands. Over 300 DXCCs on 6 bands, etc, etc. My point is that you can
do a lot with antennas at much less than what some computer program says is
optimum.
>
>
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