[TowerTalk] Can take-off angle be too low?

[Pete Smith]

At 07:46 PM 11/4/00 -0600, n4kg@juno.com wrote:
...
>It seems to me that if the ionosphere will support higher angles
>several different modes (3 hops, 4 hops, etc) will be supported.
>I *assume* that most Europeans do not have VERY high 
>antennas, i.e., most likely in the 30 to 50 ft range, and therefore
>the main lobes peak between 10 and 15 degrees with less gain
>at lower angles.  Therefore, it is often best to also have a lower
>antenna to match the angle of maximum radiation from the 
>transmitter end.  I often find my lower antennas (40 ft) better during
>the middle of openings to Europe than my higher antennas (60 and
>80 ft).


A lot of the "low angle" modes that show up in the N6BV stats are very low
indeed -- a couple of degrees.  Most real-world antennas have a very hard
time generating much signal at those angles anyway. 

All of this is susceptible to modeling with VOACAP, in case you're looking
for something else to do these long winter evenings.  The current N6BV
numbers are intended to characterize how the ionosphere behaves, without
the biases imposed by antenna patterns at either end.  But there is no
reason why, with a little work, you couldn't configure VOACAP to simulate a
hypothetical average European station (on one end) and your station (on the
other).   Or alternatively, you can use the older N6BV data, which assumed
specific antennas on each end of the circuit.

I also note that VOACAP allows you to specify the maximum acceptable
multipath echo time -- I haven't experimented with changing this parameter
to see what effect it would have, but conceivably it would squeeze out some
of the highest and lowest angle modes as generating excessive echo...



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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