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Propagation

11 Mar

Today’s note is inspired by a comment made by Leo on Brasspounder’s blog site. Leo noted that propagation is changing very fast this time of year. I second that thought and raise you five Leo!

One of the fun outcomes  of having a daily schedule over a long period of time is that you are able to get a sense of how Mother Nature moves things around on the chess board so that sometimes things are predictable and other times  you are fooled. To recap just a bit, I am engaged with a friend in Boston, every work day ( Monday through Friday), for an hour of code practice. As we progress through the seasons, Chuck uses a program called Icepac to select the best times for that particular week to schedule code practice. We generally stay on 20 Meters. We have been doing this since sometime in late spring or early summer of 2007 so we are approaching 2 continuous years of cw practice. Over that period I can only recall a single day when we were skunked and had to move from 20 to 30 followed by 40 and ultimately to 80M very late in the evening. That day was a bust!

In the Spring of the year the sun is moving very fast toward the zenith in the Northern Hemisphere. That is to say the days are getting longer and in the Fall the rate of change is very fast in the other direction towards shorter days and a lower Northern Hemisphere sun. The rapid changes are so great that this causes big distortions in Icecap predictions and from what I can see, some inaccuracies in an otherwise pretty good program. But only this year! Between this week and the previous two weeks we have moved from a “Normal” sked time of 1 to 3 PM to a Icepac predicted time of 10 AM (local) or so. Ultimately, the Icepac prediction of 10 AM only ever worked for a single day or two. This is pretty unusual in itself because Icepac has been good at predicting things for almost 2 years. When it stopped working about a week or so ago, Chuck compared it against VoaCap. We are using VoaCap now-for this time of year or until something else moves around the chess board. It appears to be more conservative and has rescued our schedule from oblivion for at least this week. We met yesterday at 2000 Z. We may have to move to 2100 Z.

As I recall in 2007 spring or early summer I was running at 200 watts. Antenna types have not changed much in these intervening years- both wire antennas. Chuck had a hard time copying me (at the 200 w level) but I had no trouble with him as he had an amp. I have since added an amp but this week he is having trouble with my signals. That could be due to an increase in noise floor at his end but more likely it is the result of a continuation in the decline of sunspots and seasonal changes. We had a higher number for sun spots last year and the year prior. It just exemplifies the subtle nature of seemingly small changes in sun spot numbers and seasonal changes that push you into the noise level when communicating at the margins. That is why it is so important to me to improve my noise situation. If you cant improve by adding a gain antenna, then optimize the receive side and get there first!

Thanks for reading my Blog. Best, Chas W7MAP/5

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Posted by on March 11, 2009 in Radio

 

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