Topband: "Too Long Beverages"/SP Contest

[Tom Rauch]

Hi Bill,

> I'm still trying to better evaluate my 4,320 foot long 84/264º Beverage
> antennna. For the SP Contest I found it not hearing Europe at all (which
> it shouldn't unless its via a bent path).  It provided much better
> reception to the Canary Islands and Hawaii than my 3 phased Beverages
> w/adjustable azimuth and my transmit parasitic vertical array. 

You need to do more than look at the pattern, and users of large 
arrays need to know something else is going on other than 
"pattern". 

At my QTH, I can look very clearly at phase shift with wide spatial 
separations. 

What I find is that if the distance is more than 1000 feet or so, the 
areas are almost NEVER in a constant phase difference let along 
amplitude relationship. The phase varies wildly, especially while the 
band is changing or if there is any geomagnetic activity.

The closer to the pole, the more wildly the phase changes. I can 
just barely use any array occupying an area larger than 1000 feet 
on Europe, and generally only when the band is stable. If the array 
gets larger than that, the outer edges of the array are in random 
phase.

Into JA, the problem is even worse. Even 300 feet of separation can 
be too much many mornings, with phase and level over that small 
distance "rolling and tumbling" so much it is impossible to keep 
the array in phase!

Compact arrays are much much more reliable than arrays that are 
spread out over a wide area, for a given pattern. I find that two 
points separated broadside even 300 feet can rotate through 360 
degrees of phase shift in a few minutes or less under many 
conditions.

What this means is we can never achieve what we might expect 
from a large array when we consider the pattern. I have a four 
antenna broadside array on 160 with 350 foot spacing and 800 foot 
Beverages that occupies a 1050x800 area. It is useful about 20% 
of the time, because of this problem. It is useless at sunset, and 
more reliable late in the evening. A similar array on JA has been, to 
this point, totally useless because the JA's all are on at sunrise 
here, when the band is changing and phase is all over the place.
           
73, Tom W8JI
w8ji@contesting.com


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