[TowerTalk] 15 meter yagi height for 6000 miles

[dotravel at aol.com]

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 at cis-broadband.com>
To: towertalk <towertalk at 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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