[TowerTalk] Monoband Yagi stacking heights and propagation (long)

[Pete Smith]

At 07:47 AM 10/14/00 -0600, n4kg@juno.com wrote:
>...Remember, most of the DX stations are using
>LOW antennas SO, when the ionosphere will
>support higher angles (i.e. during the day),
>higher angles may produce greater signal strength
>than low angles because your peak angle
>is matched to the peak angle of the DX.

Interesting -- I think this is the first time I've heard this particular
point made (about the antennas on the other end).  Makes a lot of sense to me.

For what follows, everyone please note that I'm aware of the caveats and
shortcomings of propagation prediction for a spot event.  Nonetheless, the
following is an excerpt from a VOACAP run for November 2000, made assuming
very high solar flux (over 200), for the path between my QTH in WV and
Frankfurt Germany at 1900Z:

SUMMARY    4 MODES   FREQ =  14.0 MHZ  UT =  19.0
                                                      Most REL
                 3.F2      4.F2      4.F2      4. E       3.F2
  ANGLE          8.68     15.64     26.90      4.92       8.68
  SIG. POW.   -131.54   -138.71   -191.10  -1201.53    -130.78

This run assumes isotropic antennas on each end.  What it says to me is
that for the DX to be stronger at my end (before my antenna selection comes
into play), his signal at 15.64 degrees takeoff angle (4 F2 hops) only has
to be ~7.2 dB stronger than at 8.68 degrees (3 F2 hops).  Considering the
depth of the null below the first lobe of most real-world antennas, that's
pretty plausible.  The second 4F2 mode at 26.9 degrees is a little less
plausible, since the DX signal at that angle would have to be at least 60
dB louder than at 8.68 degrees.  Still, that too could happen.  If my
antenna has a narrow first lobe and null depth above the 11 degree first
lobe of, say, 20 dB, it's not hard to see how we could miss each other
entirely!

Interestingly, at a SSN of 110 (corresponding roughly to a solar flux of
160), the higher angle propagation modes aren't predicted to be present at
all in November at that time of day between here and Europe, on any band
14-28 MHz.  Instead the only propagation modes available are at 6-9 degrees
(the higher number at 14 MHz).  Could do a lot to explain the mid-opening
doldrums, particularly if you've already worked most of the folks who are
strong at the lower angles.

One final observation -- at least in this quick look, it appears that this
phenomenon is most pronounced on the path to Europe at frequencies well
below the MUF.  For example, at an SSN of 160 in November at 1900Z, VOACAP
predicts only two modes on 21 MHz, with a maximum angle of 11 degrees, and
only one on 10, at a maximum of 7 degrees.  So if you deplete 10 and 15 the
first day of CQWW, your low antenna will probably come in handy on 20 to
Europe the second afternoon.  For that matter, it will almost always be the
best antenna to the south, but then we knew that, right?

73, and pray to the sun god,

Pete N4ZR

73, Pete Smith N4ZR

Contesting is ... Extreme Radio

The World Contest Station Database 
is back up and running at
http://www.qsl.net/n4zr 



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