[NLRS] 2 meter antenna elevation

[Dr. Gerald N. Johnson]

528 feet at one mile is 5.7 degrees. 528 feet at one half mile is 11.3
degrees.

If there was significant energy bouncing back from the bluffs, it would
affect the SWR of the antenna. One time in a lab where I had a return
loss bridge hooked to a 432 yagi and the feed matched to showing more
than 30 dB return loss, I could detect people passing through the
antenna pattern 30 or 40 feet away. But that didn't run the return loss
up to 10 dB or less, it was changing on a few dB at that sensitive
matched condition. 10 dB return loss is a SWR of 1.22, 30 dB return loss
is a SWR of 1.002, difficult to measure outside the lab and then only
with a return loss bridge, not with a SWR meter.

The elevation angles for long distance tropo are difficult to predict 
and may be high or low. Sporadic E arrival angles tends to be high, so 
that a 6m beam at 30 feet gets a stronger signal than one at 60' though 
W0WOI who has his arranged for switching has quit telling distant hams 
worked on E that the lower beam was stronger, they didn't believe him. 
But its true because the vertical angle from the lower beam is higher. 
That's less pronounced at 2m though I've worked Connecticut a couple 
times with a 5 element yagi the first time at 6 feet and the second time 
about 6 feet about my house roof.

73, Jerry, K0CQ

On 7/26/2011 12:22 PM, Ken Boston wrote:
>
>
> 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
>