[Towertalk] Re: [Towertalk] 20M Yagi ?

[i4jmy@iol.it]

In case of a 200/300' real drop, and 800' hill top location, it's quite 
possible that the first reflection is so far that the equivalent height 
of the antenna/s from ground is 800'.
In such case stacking will affect gain but is almost useless for null's 
coverage and to obtain a smooth and wide lobe or higher angles 
radiation, ground is anyway too far down.
I didn't try or study it, but I think a vertical polarization could be 
a (compromise) solution for high angles and smooth wider lobe at a 
sacrifice of some gain, in such peculiar cases.
On the other end an height of 800' is already in excess of 10 WL, lobes 
and nulls will be at so close intervals (few degs) making the situation 
less critical than one might think in the other cases. 

73,
Mauri I4JMY

> WD4K wrote:
> >The qth here is on an 800' hilltop with 200-300' drop and horizon 
> in the three main directions. Any suggestions before I start planning 
> this next project?
> 
> 	This is a very complex question best answered with:
> 
> 1.  N6BV's Terrain Analysis (YT) available with recent ARRL Antenna
> Handbooks (but it does not handle out of phase antennas).
> 
> 2.  NEC modeling of two stacked yagi's with BIP/BOP (both in phase
> and both out of phase) as well as the individual patterns.
> 
> 3.  Actually, K6STI's Terrain Analysis (TA) would be the very best 
> since it combines 1 and 2 above, but I'm not sure Brian is still 
> selling it.  His e-mail is k6sti@n2.net
> 
> 	My personal guess is that you would be better off with two 
> medium Yagi's (like 204BA's) at 40' and 90' with the ability to do 
> either and BIP/BOP than you would with a single monster Yagi.  Given 
> your effective height, you have to be careful to not get only low 
> angles.  From here in NC, there are two predominant angles to Europe 
> on 20 meters (1-3 degrees and 7-8 degrees) and a single antenna will 
> probably not cover both well.
> 
> 						73,  Bill  W4ZV