[NLRS] 2m enhancement from EN24

Tue Jul 11 22:56:24 EDT 2017

Decades ago there was an ARRL book titled "Beyond Line of Sight" that 
talked a lot (based on QST articles) about weather effects on VHF 
propagation. Its still valid reading.

73, Jerry, K0CQ

On 7/11/2017 9:33 PM, Karl Heil wrote:
> Thanks for posting this Jerry.  I always enjoy learning from you.
>
> 73,
> Karl Heil
> WD9BGA
> EN53ba
>
> BTW, I did work Mary from my home station abt an hour ago on both 2 and
> 432.
>
> -----Original Message----- From: Dr. Gerald N. Johnson
> Sent: Tuesday, July 11, 2017 8:50 PM
> To: nlrs at mailman.qth.net
> Subject: Re: [NLRS] 2m enhancement from EN24
>
>
>
> Weather fronts like we have had the last couple days are often very
> effective at enhancing VHF and microwave propagation. Often there is
> warm air over running cold air and that reverses the normal temperature
> gradient and causes a great deal more refraction. And can trap signals
> to propagate in the front as if in a waveguide.
>
> I saw a strong example of that one Sunday I think about 1976. My TV in
> the kitchen was seeing a Milwaukee WI UHF TV station with just a single
> telecoping rod antenna. That was from a mile south of Gilbert Iowa,
> probably a distance of 300 miles. A strong front that in a short while
> created a super cell and a tornado on the ground a mile in diameter
> located south of Ogden Iowa about 20 miles from Gilbert but visible from
> my back porch. That tornado dissipated and another formed near the tiny
> town of Jordon. The Jordon tornado was also a mile wide and rotating
> reversed to normal tornadoes. Jordon was about 5 miles south and 8 miles
> west of my house. The tornado passed about two miles west of me,
> dropping a side funnel that broke up after draining the Gilbert sewage
> lagoon. It dropped debris about 200 yards from my house. There was
> another side funnel that I didn't see that went past my house about 3/8
> mile east that did damage. The main funnel sometimes lifted over houses
> but in fields it looked like the field had been graded with a mile wide
> grader blade. It went on NNE and lifted up at Story City, damaging the
> tall enclosed tower at the fire department where they dried hoses.
>
> The radio noise from that thunderhead was so great that the county
> deputies couldn't hear their dispatcher in Nevade about 12 miles SE of
> Gilbert. After the funnels had moved on I went into Gilbert to WB0BQV's
> house where he had his generator running and had been supplied a county
> sheriff's radio for such emergencies by the local civil defense
> director. We relayed for the dispatcher for a while, then as the storm
> moved on we learned that the mutual aid radio at the hospital in Story
> City wasn't working so we went to see what was wrong. We climbed up to
> the roof and found 18" of water on the flat roof. The tornado had
> dropped a bunch of tree leaves that blocked the drains. And it had blown
> over the antenna. While Dave fixed the antenna I took off my shoes and
> rolled up my pant legs and waded to the drain and cleaned off the
> leaves. That was a lot of weight on that roof.
>
> The amazing thing for the afternoon that there was only one injury in
> the miles the big funnels were on or close to the ground, an arm broken
> by a falling limb in Story City.
>
> Lots of effects along that front. Contents from some of the damaged farm
> house like books and checks were found 80 or 90 miles NE in a day or
> two.The little town of Jordon is mostly a memory now, most of it was
> blown down by the tornado.
>
> Another very good creator of long VHF and up propagation can be a
> stationary high pressure dome. I've worked 1296 from Gilbert to Dallas
> Texas with 2.35 watts and to Houston on 432 with 100 watts while under
> such a stationary high pressure dome. It also causes a wide area
> temperature inversion preserved by calm winds.
>
> A calm cloudless morning without any other weather features often shows
> enhanced propagation due to a temperture inversion. The inversion is
> cured by breezes mixing the lower atmosphere. The inversion is caused by
> radiant cooling (on a clear night) of the earth's surface often
> significantlly cooler than the air at the NWS standard elevation of 6
> feet. I have software running for decades now at weather.net that
> compares cloud temperature to surface temperature to tell clouds from
> cooled ground and uses the clouds as a mask for radar to mask out odd
> propagation (Anomalous Propagation) echoes. In use its been found that
> the satellite temperature data threshold has to be set as much as 15
> degrees fahrenheit below the official observation dew point sometimes to
> keep from judging the radiant cooled earth surface as a cloud.
> Especially on a calm clear night.
>
> 73, Jerry, K0CQ
>
> On 7/10/2017 8:26 PM, Mary Brown wrote:
>>
>>
>> WD9BGA/b(EN53, 144.296ish) is 5x6 and N0LL/b(EM09, 144.294ish) is 5x2
>> into
>> EN24, as the sun sets conditions may improve with this still air.
>>
>>
>>
>> Mary
>>
>> W0AAT
>>
>>
>>
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