NON DUCTING TROPO - better 70cm over 2m

This information will be built upon as conditions prevail

Thanks to some reports from VK3VSW and VK5ZMB, plus observations by myself on 70cm in the last few days and some reports from VK5ACY on Kangaroo Island, it would seem we have have evidence for 70 cm Non Ducting Tropo.
 
Initially I think Chris VK3VSW in Geelong was the first to report:
 
"Just worked VK7LCW - Peter on both 2 & 70cm this evening at around 10:15 UTC. Signals on 70cm were very very good, 5 X 9+ 20dB, 2 Meters were 5 X 3...... interesting............."
 
Then Brian VK5ZMB in Gawler :
 
"There has been good 70cm ducting tonight between my QTH (Gawler 40 Km north of Adelaide) and Pt Lincoln, approx. 250 Km's. The Pt Lincoln repeater has been a steady S7 to 8 all evening and I managed to work VK5RF via the repeater. Strangely though I could not hear the Pt Lincoln 2m repeater which I regularly can hear and was S9 most of yesterday."
 
Bill VK5ACY on Kangaroo Island did not send an email, but reported on the VK/ZL Logger about good 70cm conditions to Mt Gambier beacon, but not as good on 2m. (from memory, at the time I did not take much notice).
 
Yesterday, here at The Rock, during the day, I noted extended range with reasonable signals during the day, but with very bad fading or QSB. At times I would describe it as 'violent' crashes of the signal into the noise then back up to some thing like S9 in some cases. At times this could occur at every 10 seconds or so. I also noted an extremely low background noise level, much lower than normal, which gradually rose again later in the afternoon.
I did not note the exact timing, but some time around 10 pm I noted signals from 2m repeaters were quite good, and were extremely stable, no QSB at all. Bendigo, 314 Km away was constant S9, Macedon 324 km was S7-8. Someone triggered the Macedon 70cm repeater which caused me to check 70cm. I noted Bendigo 70cm at S9+40dB, though I did not turn the antenna's directly on to Macedon 70cm , it was something like S9+10dB. I could also get the Grampians 70cm at 471 Km at about an S7 nothing from there on 2m.
 
I read some information on so called NDT this morning.
 
Some points -
 
  1. Is commonest during high pressure conditions. NDT is often best when the high pressure is in decline and moving east.
  2. Occurs at VHF, UHF and higher frequencies, longer wavelengths do not usually enjoy as good NDT as shorter ones.
  3. Best conditions usually occur early morning or late evening.
  4. Fading (QSB) is a problem. May be slow and very deep. May include faster 'flutter' fading.
From the above points, I have underlined some parts which I thought were of particular relevance to what was observed in the past week.
 
From point number 1, we were in in the tail end of the current high pressure system moving east.
Point number 2, 70cm was much better than 2m.
Point 3, late evenings was generally noted.
Point 4, although none of the other stations that submitted reports mentioned QSB, I did note very bad QSB here during the day.
 
I have attached a Duct graph taken at 12z 13.10.03 from Adelaide. Around the time of Brians and Chris's reports. The graph may not come through to some people, but I took info well up into the troposphere and there is no ducting at all. I also took data from Melbourne and Wagga (near my QTH). They all show normal atmosphere, no ducting, they are all the same as the Adelaide graph so I have not attached them. The graphs do show a small ground based Super refractive layer in each case, but I would really consider this to be a more localised effect. But I dont really know.
Considering the height of the Macedon and Grampians repeaters (over 1000masl) and not being sure of the Bendigo repeaters height above normal ground level, I would be thinking the ground based super layer is not the cause of this condition.
 
There may be another condition which I can not view that caused this occurance. It certainly was not ducting. It may have been the small super refractive layer, but with signals like this its doubtfull.

Leigh VK2KRR