Topband: Daylight QSO's during the SP
W2RU - Bud Hippisley
W2RU at frontiernet.net
Mon Dec 31 08:52:21 EST 2007
Sent: Monday, December 31, 2007 6:45 AM
Subject: Topband: Daylight QSO's during the SP
...I was under the impression that, like
commericial AM stations, 160 was limited to ground wave propagation during
most of the day.
What would be driving the propagation in the middle of the day? The fact
that we are at the absolute bottom of the sunspot cycle, and the dead of
winter with the sun low on the horizion has to be part of it....Is this
rare or common on 160?
I'm no propagation expert but I believe the only limit to daytime distance
on 160 is running enough power and antenna gain to overcome the total path
loss which is largely a (D-layer) absorption matter. As you note, we're at
a sunspot minimum, we're at the shortest daylight portion of the year, and
on any given day the tarot cards can line up to minimize the absorption.
Voila! Long distances.
In general, the closer your operating frequency is to the MUF, the less
absorption you experience. The MUF has not been getting very high lately;
40 meters is useless here at latitude 43.75N by suppertime, and most nights
the skip on 80 has gone "long" by 0000Z - 0100Z. I know that last statistic
*very* well, because my evening traffic net on 80 is severely hampered on
those nights. What I don't know as accurately is how long it's taking the
MUF to climb back up each morning.
A related matter is that it has been possible to routinely work Europeans
from here in the northeastern USA via short path on 40 most days this
winter. I'm listening to SM4OTI barrel in on 7004 as I type this at 1340Z.
I'm used to having an occasional long path opening to Europe right around
sunrise here, but this short path stuff has been audible all day long --
even at noontime!
Back to 160. Compared to a decade or two ago, we have many more stations
active on 160, we have receivers with better dynamic range, we're running
higher power on average, we're much smarter about antenna efficiency issues,
some folks have directional patterns on TX and/or RX, and we're getting
smarter about how to keep our feedlines from picking up extraneous noise.
So on balance, being able to work daytime "DX" on 160 isn't anywhere near
as unusual as we used to believe. To answer your question: It *was* rare,
but it's becoming commonplace -- during sunspot minima, at least.
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