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[Towertalk] Re: [Antennas] Comparison!!

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Subject: [Towertalk] Re: [Antennas] Comparison!!
From: (Tom Rauch)
Date: Tue, 16 Jul 2002 09:19:21 -0400
> My plans are to put one at the top of my 110 foot rotation tower (see
> .  With the property at over 2000 feet above sea

They make terrible lightning rods, and the precipitation static on 
almost any top mounted antenna will kill the receiver during storms. 

My personal selection, after much thought, was a DB224E four-dipole 
array. It has nearly the same gain, but will take lightning hit after 
lightning hit without problems.

For precipitation static, I'm side mounting a cheap MFJ 17-foot long 
dual band fiberglass antenna. It has just slightly less gain on two 
meters than the Station Master or 4-dipole array, but only costs a 
hundred bucks. I'll switch to it during bad weather, and use it on 
70cm during other times.

> level on top of this mountain, it should work gang busters.  I am also

Maybe, but height AMSL doesn't mean squat for anything except working 
ships at sea. I have huge problems convincing people the best spots 
are not always "the highest spot between here and Florida". I have a 
friend who has a terrible VHF/UHF radio location because he has high 
surrounding ridges in the distance, and big power lines that wipe out 
HF reception. But the exceptionally poor site does look OK as far as 
AMSL height goes.

The proper parameter is HAAT, with obstructions on the path 
considered. One huge problem with mountains is they usually have 
other mountains around, and by themselves are pretty "fat". Those 
effects can cause big dead spots despite high ASL. Antennas also can 
lose a few dB because of lack of downtilt in pattern, so you might 
want to look at that.

Just be sure the mountain itself does not shield the path to desired 
stations, or even get close to doing that! Even if the path slightly 
clears the earth you can get big time nulls caused by scattering that 
are not correctable just by adding downtilt.    

> going two install (2) Cubex 8 element 2 meter quads (vertically
> stacked) at the 80-90 foot mark for pin point communications.  Of

I'd stack something with a more useful gain pattern, like yagis. 
Quads are really just two 1/2 length element yagis stacked 1/4 wl 
apart. When you stack quads, they actually work worse than the same 
stacking distance when stacking yagis.

As a matter of fact, a small gain advantage of quads over a similar 
spaced yagi only applies to one, two, or three element quads in 
freespace. That advantage totally disappears with longer arrays, or 
if you stack the antenna in the H plane of each antenna.

If you are serious about having a good signal, I'd rethink the system 
a bit and look closer before doing anything.73, Tom W8JI 

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