[NLRS] 2m enhancement from EN24

Tue Jul 11 23:47:16 EDT 2017

Loaned that out and it never came back... good reading!

-----Original Message-----
From: nlrs-bounces at mailman.qth.net [mailto:nlrs-bounces at mailman.qth.net] On
Behalf Of Dr. Gerald N. Johnson
Sent: Tuesday, July 11, 2017 9:56 PM
To: Karl Heil; NLRS Reflector
Subject: Re: [NLRS] 2m enhancement from EN24

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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