[Elecraft] RE: Low Antenna on Mountain Top

[Geoffrey Mackenzie-Kennedy]

Ed, WA3WSJ wrote:

> >Recently I compared a 40m dipole fed with 300 ohm ladder line
> up 20 feet to a ground-mounted vertical on a 100 foot cliff at Turkey
> Point Lighthouse, MD. The vertical beat the dipole by around two
> S-Units.

Bill, W4ZV wrote:

>         Interesting.  I had just the opposite
> experience in the recent Flight of the Bumblebees
> test.  I was using an 88' doublet with 40' apex and 25'
> ends fed with 300 ohm line to an Emtech ZM-2 versus
> a Par End-Fed 20/40 Half Wave Vertical.  The doublet
> was almost always better than the vertical although
> there were a few times when the vertical was clearly
> better.  This was on a mountain top about 300' above
> average surrounding terrain.  I did a lot of comparing
> signals on both 20m and 40m during the test.

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It is my understanding that the vertical pattern of a half wave vertical 
splits up into several narrow lobes when it is installed on top of a 
'narrow' mountain top, with the dominant lobe being at the lowest TOA. 
Because of the nulls, the incoming signal has to be arriving at just the 
right angle plus and minus not very much for the vertical to be seen as 
better than a doublet at the same location. The doublet has the broad 
vertical lobe.This might explain Bill's experience.

When the vertical is placed on a cliff edge, I would suspect that some null 
filling could take place, especially if the vertical is a ground mounted 
quarter wave. However I think that it would be very difficult to model such 
a situation with any accuracy - what is the pattern of ground currents for 
starters? This antenna no doubt benefits from zero obstructions and little 
ground loss over the cliff's edge.

If propagation is via the E layer, the angles of arrival are low - about 14 
degrees for a 500 mile hop and 4 degrees for a 1000 mile hop. So a 'DX' 
antenna is also a good antenna for short haul - if the E layer is involved.

73,
Geoff
GM4ESD