[NLRS] 2 meter antenna elevation

[Dr. Gerald N. Johnson]

Digging out my 2010 CSVHF proceedings, I find the article is by W0FY on 
pages 101-106. It is on 6m and illustrates the fine elevation pattern 
details caused by the diffraction grating effect. Searching I find it 
was published on line a couple years before at:
http://www.w9smc.com/blackhole/news%2010%2008.pdf

He found that the lowest lobe was attenuated by tilting a 6m beam, and 
that lowest lobe was at a high enough elevation to get over W9RPM's 
cliffs. It would be better the compute with Manna-Gal than EZNEC and to 
use W9RPM's actual 2m beam and height because antenna height has a big 
effect on the diffraction grating elevation pattern. I found it very 
interesting to see that elevation pattern by listening to a satellite 
beacon on 2m as the orbit rose or fell near vertically on a selected 
pass. That's a good long range antenna range test.

W9RPM's cliffs are shadowing closer station and antenna tilt isn't going 
to help. Only much greater antenna height or moving up on top the cliffs 
is going to help that. The longer range stations will be dropping over 
the cliff anyway.

Fact is VHF and UHF signals from beyond the horizon do propagate at an 
angle. The longer range signals are refracted in the atmosphere by the 
normal change in air density with height and that refracts rising 
signals back down. Temperature inversions increase the refraction.

I know on some fairly long microwave links that two antennas are 
sometimes used at each end, one for the normal refraction and another 
pair with greater elevation for the temperature inversion events to get 
better reliability on a path. But those antennas probably have closer to 
1 degree beamwidths while the practical 2m yagi is closer to 30 degrees 
beamwidth. (And my next ones will have even greater azimuth beamwidth 
for easier aiming.)

73, Jerry, K0CQ

On 7/24/2011 12:29 PM, Bruce Richardson wrote:
>
>
> I was just discussing this with John on the phone and encouraged him
> to come to the list.
>
> We know that a guy on the ridge does better than a guy in the valley.
> In John's case, he really is quite close to the blocking ridge and
> blasting right into the side of it.  Isn't it true that our 2m signals
> get scattered by reflection and dispersion off of trees, rocks,
> buildings, and ridges?  Doesn't this end up being forward scattered by
> dust particles and water molecules?
>
> Two questions: by blasting into the side of the ridge, might he be
> getting back-scatter that is phase cancelling some of his signal?
> Secondly, I know curvature of the earth plays into this a bit, but I'm
> wondering if by elevating, he might lift that main lobe above the
> ridge and strictly work on dust particle scatter to the eastward
> (Milwaukee and beyond).
>
> Dr Jerry has already replied and is kinda indicating how sharp the
> lobe would have to be to get the intended benenfit.  Anyways,
> interesting topic and I look forward to follow-on discussion. I'm
> working on some graphics from RadioMobile to show the dilemma. I'll
> post links to them when the graphics are ready. Might be tomorrow.
>
> 73
> Bruce W9FZ
>
>