[NLRS] 2 meter antenna elevation

[tom ring]

I used to live in Potsdam NY and would often watch this newcomer to the 
television world, Public Television.  Which was on locally as WNPE/WNPI at that 
time.  Now has the unfortunate moniker of WPBS.  ;)

And it also used to have a problem - when it got really hot the apparent signal 
to noise in my coverage area would go to zero for some long period of time and 
come back when it cooled off.  Even though the signal to noise from our local 
transmitter was as good as it got.

The local cable company, which I subscribed to, and the local signal, which I 
had an antenna for, both showed the same intermittant problem from the local 
transmitter. I contacted the station and was informed that the northern 
transmitter was fed via a microwave link.  They stated that "when conditions 
were right, the signal just ran into the ground".

This was a single hop from Watertown (more likely Carthage) to a location I 
don't recall but may have been near Norwood or Canton.  50 to 70 miles would 
bound it.  And NNY is hilly with older weathered mountains as you go east, so 
the 70 (or a lot more) miles is fairly easy as long as no other hill is in the 
way.

tom
K0TAR

On 24 Jul 2011 at 13:16, Dr. Gerald N. Johnson wrote:

> 
> 
> 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
> >
> >
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