[TowerTalk] Arrival angles and sunspot number

[k6ll@juno.com]

On Sun, 23 Apr 2000 18:29:15 +0000 Pete Smith <n4zr@contesting.com>
writes:
> 
> The arrival angle tables calculated by N6BV and included with the 
> Antenna
> Book and YT are averaged over the full range of sunsport numbers and 
> times
> of year.  does anyone know if there is a systematic variation in 
> these
> angles with sunspot number?  In other words, during a peak should 
> these
> numbers be systematically biased in a particular direction -- for 
> example,
> is there relatively more high-angle propagation over a given path 
> under
> high-sunspot conditions?  Are such generalizations possible, if only 
> on a
> band-by-band basis?  I don't have a copy of "All the Right Angles," 
> which I
> assume has the raw data, but I'm hoping someone has already 
> researched this.
> 
> I'm looking for the answer in connection with a possible new way of
> evaluating antennas that I'm developing.
> 
> Thanks for comments.

I don't claim to have made a comprehensive study, but just
spent about 30 minutes with VOACAP looking at arrival angles
with sunspots varying from 60 to 180.

It looks to me like the key question is "How far below the MUF
am I being forced to operate?" For example, if the MUF on a
given path is 20.9 Mhz, contest operation will have to take
place on 14 Mhz, well below the MUF. Under these conditions,
arrival angles will be much higher. Arrival angles are generally
lowest just at and below the MUF, and increase as the difference
between the MUF and the operating frequency increases. 

When sunspots are high, the slope of the MUF curve is steeper,
and the bands seem to open almost all at once. A single-op
station just gravitates to the highest frequency band open, and
you are soon on 10 meters. If the MUF keeps on going, like up to 50 Mhz,
the arrival angles will be high even on 10. The 20 meter station at
a multi-op, forced to stay way below the MUF, will be dealing with
some very high arrival angles under these conditions.

It's pretty easy to run VOACAP, varying only the sunspot number, and
see what happens to the angle on a given path. I usually use
"Isotropic+10dB" as the transmit antenna and "SW Whip" as the
receive antenna.

In a nutshell, I don't think you can say, as a blanket generality,
that angles are always higher during periods of high sunspots. High
angles occur also during periods of low sunspots, such as on 20 meters
when 15 is not open.

Dave Hachadorian, K6LL
Yuma, AZ
K6LL@juno.com
























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