[NLRS] 2 meter antenna elevation

[Ken Boston]

John;

First thing you should do is do some simple math and get a handle on just how much of an angle is formed by the blockage to your east.

(You mention 400-550 ft bluffs, but need to get more precise)

Find the height in feet above sea level for your house.  Add the height in feet of your tower. This will be your home benchmark.
>From geo maps, or someones GPS who is out on the bluffs at the point for your direction east, obtain the height in feet above sea level.
Take this number and subtract the home+tower number.  This value is the height in feet that the bluffs are higher than you.

To get the angle; Tangent of the angle equals the height number divided by the distance in feet from your house to the edge of the bluffs where they 'peak' in height, needed from a good map or mapping program.  You can do this for each direction, like E, ESE, ENE, which you call radients.

For example: (these numbers are guesses!!)

Benchmark at home location; 	800'  ASL
Tower height;		     	 80'
				   	----
Home benchmark:		    	880'   ASL

Bluffs at point on radient:	1300'  ASL
Subtract home benchmk:		-880'	 ASL
					____
Difference in height		 420'

Distance to bluffs on radient: 5280'  (one mile in feet)

Tangent (angle) = 420/5280,  so angle= 4.5 degrees.

My guess is that the angles above 4-5 degrees MIGHT benefit from an uptilt of the beam, to allow more energy to reach the troposphere or ionosphere.
This would be more evident on modes that thrive on higher arrival angles, such as single hop E skip, and troposcatter.  You may gain nothing on modes thriving on lower angle entry into the propagation path, such as F2 and long haul multi-hop E skip. I doubt that you are getting much cancellation of signal by return scattering of your own transmitted signal, as not that much of your forward power is returning to your antenna.  More calculations would be needed to see if the ground gain present in front of the antenna is still present once the departing wavefront reaches the bluffs. 

If your calculations in various directions leave angles below about 3 degrees, I would guess that uptilting would buy little help.  The only way you are going to experience height gain, is by actually getting the height, leaving your antenna viewing a 'negative' horizon.

Ken  W9GA

-----Original Message-----
From: nlrs-bounces at mailman.qth.net [mailto:nlrs-bounces at mailman.qth.net] On Behalf Of W9RPM
Sent: Sunday, July 24, 2011 11:56 AM
To: nlrs at mailman.qth.net
Subject: [NLRS] 2 meter antenna elevation



Hi, I have a question to pose to the group. I have 400-550 ft bluffs 
that run to the NE-E-SE of me. These are anywhere from 3/4 to a mile to 
the east, and then a little more as you go North or South. I am in La 
Crosse down in the valley. I am curious as to what if any benefit 
elevating my antenna say 10 degrees or so on the tower. It is between my 
80 and 40 m antennas, so a EL Rotor would not help. This would be fixed. 
Any thoughts on the Pro's and Con's of this. Thanks, John W9RPM

-- 
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