[NLRS] 2 meter antenna elevation

[Dr. Gerald N. Johnson]

Same problem when there was more than the normal 4/3 earth radius 
refraction they needed more elevation on their dishes or a second set 
like I described.

73, Jerry, K0CQ

On 7/26/2011 9:56 PM, tom ring wrote:
>
>
> 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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