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Old 12-04-2013, 10:19 AM
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DaveInDenver DaveInDenver is offline
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Join Date: Jun 2006
Location: Larimer County
Posts: 8,469

That's a cool VHF skip you guys came across. If you look at the solar data 11/22/13 was a pretty quiet day so not sure what phenomenon was at work. NOAA did release a geomagnetic warning on 23NOV2013 at 0800-1700 UTC for a K-index increase to 4, which indicts a pretty active storm in the atmosphere. But there weren't a ton of flares.

Usually VHF and higher just passes right through the atmosphere but low VHF will experience sporadic E-layer reflection, which is a one-hop skip of a couple of hundred miles, and ducting where your signal gets caught in a regional layer that can travel much farther. Our 2m band is really the upper limit for this to happen commonly, it's more likely and almost predictable in 6m and sometimes 10m. It's happened on 70cm but it's extremely rare and once in a while on 1.25m.

Our winter solstice is a common time for a trans-equatorial contact on 10 and 6 because E-layer phenomenon peak during summer. So if the atmosphere is particularly active the region of activity reaches us. If you polarize your antenna horizontally and orient it for north-south, you can almost always count on a contact. This is because the skip generally changes the signal polarity, so a vertical incident wave will end up horizontal.

Being cross polarized (IOW always listening with a horizontal whip when the incident signal has been vertically polarized) means you are giving up 20dB of signal strength. Since a dipole for 2m is only 38" long you can rig one up very easily! 20dB is like using 0.5W instead of 50W or roughly 3.5 S-units, so the field strength goes down A LOT when you're out of polarization.

That you guys had a horizontal-to-horizontal contact indicates it was probably a duct rather than simple skip, which is more unusual and probably due to weather rather than the sun. Thunderstorms will create local skips in the summer, for example you might hear Breckenridge or something else not line-of-sight.

It works very well north due to the semi-permanent nature of the aurora over the pole, BTW. So people with 2m beams will point them towards Russia and northern Europe with some success.

What is also fun is talking FM on 6m and 10m repeaters in New York or Washington... There are I think eight repeater pairs on 10m recommended by the ARRL nationally, so you can monitor them all to see what paths you might have.
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