On Tue, 12 Dec 2006 23:45:42 -0500, "Jimmie D"
wrote:


"Owen Duffy" wrote in message
.. .
On Tue, 12 Dec 2006 22:18:42 -0500, "Jimmie D"
wrote:

This afternoon while cleaning a closet I pulled out an old US map that had
been marked with contacts I made back when I worked 10M a lot. After the
local stations there is a big empty area on the map then I started making
contacts again at about 300 miles. Antenna used was a 1/4 lambda
groundplane
with the radials drooping so to match 50 ohms. A chart I found indicates
that this means I have a vertical angle of radiation of 50 to 60 degrees.
Is
this correct??. I didnt think the angle would be so great for this
antenna.

BTW the antenna was about 30 ft off the ground when in use.
Jimmie


Would the skip zone (the gap between where ground wave peters out and
where sky wave is sufficiently low angle to refract in the ionosphere)
explain your observation?

Owen
--

Yes but the chart I have seems to be telling me that the distance to the
first skip zone has a direct correlation with radiation angle with 300 miles
being indicated for an antenna with a 50 or 60 degree angle . Is this
correct? I was thinking this particular antenna would have a lower radiation
angle but I am beginning to think this may be typical of the drooping radial
1/4 wl antena.


J,

If I treat the earth as flat, and figure that the propagation is via
F2 layer, say at virtual height 300km, the the rise is 300km for a run
of half of 300mi, or 240km, so the angle of departure is 51 deg.

The refraction mechanism is sharp cut-off, higher angle of incidence
will not refract.

We don't know what the pattern on your antenna is, but even though it
may have some sharp deep nulls, it is most unlikely to exhibit a total
cutoff above that 50 to 60 degree number you have proposed.

Antenna patterns influence things, but exceeding the MUF on a path
assures you of no propagation, the MUF dominates. Sure the MUF varies
over time, but your historical observations probably just capture the
highest MUF that occured with some small probability, depending on how
much time you put in to collecting the QSOs.

Owen
--