[NLRS] COLD weather 10Ghz prop

[Donn Baker - WA2VOI/0]

Hi Bill,
Good observation !  And good question, too.
It may well be related to ice crystals in the mid-layers of the atmosphere.  There has been similar data published by 
Bob Larkin, W7PUA, et al in QEX.  (Available online at http://www2.arrl.org/qex/larkin.pdf)  There, he's talking about 
upper atmosphere ice and scattering, but I'd be willing to bet that you're seeing similar conditions with cold, 
relatively moist air at much lower altitudes.

At coffee Tuesday nite, Dave, N0KP joked about 10GHz being the new "Magic Band."  I think he's right !!

73 Donn
WA2VOI/0


----- Original Message ----- 
From: "Bill Davis Jr" <cqbilld at msn.com>
To: <nlrs at mailman.qth.net>
Sent: Friday, December 14, 2007 8:06 PM
Subject: [NLRS] COLD weather 10Ghz prop


>
>
> Hello guys
>
>  At first I was going to pose this observation to the 10Ghz mailer group and then I changed my mind. Perhaps there are 
> people that or on this mailer and are not on the 10Ghz list that have ideas relating to an observation.
>
>  Since the winds messed Gary W0GHZ's towers up this summer, Gary and I continue to "test" the 155mile somewhat 
> obstructed 10Ghz path daily. I think I am seeing a pattern that I really don't have a clue about ...
>
> Garys 10Ghz dish/system is a few feet lower than before because of the damage to the top section of the crank up 
> tower, lower by 10ft of so from before. It seems that the path is somewhat more challenging than before. Under 
> non-winter conditions, we work pretty much any time. But once the weather get sub-freezing the path becomes more 
> difficult. I can almost always see Gary signal on the Softrock SDR IF system.. the signal tends to be just above the 
> noise with  excursions to perhaps 6 or 7db above the noise. The signal will exhibit no scattering.. the signal will be 
> a VERY narrow spike with "Normally" considerable QSO ... too weak to copy and sometimes to eweak to hear, but 
> observable.
>
>  BUT .... When the temp is well below zero at my end ... maybe -10deg F or colder (not cast in stone) the signal 
> characteristics change. I see MORE scattering of the signal, the "spike" on the panadaptor is no longer a pixel wide 
> but often is several wide, PLUS it seems often the signal is stronger by 5 or 6db. Also often less QSB is observed. NO 
> observation of radar returns have been made under these condition. I have labeled this prop "cold wx tropo" in Gary 
> and my conversations.
>
>  Our data set is still pretty small, but growing.
>
>  What might explain the difference in prop between +10deg F and -10deg F?? Gary and I again this morning (while I was 
> at Minus 12deg and he was at 0deg) had a nice 5-1 QSO .. this was the case several times last week when we were in the 
> icebox around -20deg. Earlier this week at 10 or 12 deg ABOVE zero ... the  sig was observable but weaker and no Q 
> resulted.
>
>  On one occasion it appeared that a few deg of elevation at Gary end improved the signal, but this has only been 
> observed one. There was some QSB during this QSO. Again no radar returns on MSP or DLH radar but Gary observed clouds 
> to the north. The temp that day here was around -17deg.
>
>  Most of the so called "city heat bubble" would behind Gary in our path, for what it is worth.
>
>  Gary and I both run right at 6 to 8 watts to the feed of an 18" offset dish. My dish is at 56ft and sees nothing in 
> the path for the first 3 or 4 miles, then multiple ridges that extend into the path by about 100ft, these ridges are 
> less than 10 miles from my location.
>
>  Gary's dish is at about 40ft ... looking across "open" suburbia ...
>
>  Any Ideas ??? or similar observations??
>
>