[TowerTalk] Two 15M stacking

[Michael Keane K1MK]

At 09:29 AM 2/25/07, TexasRF at aol.com wrote:
>
>One added thought that will help reconcile K1TTT's experience with others  on
>this subject:
>
> From K1TTT into Europe, say a 3500 mile path,  a 54 degree angle 
> will  have a
>3dB coverage of about 3200 miles in width. From this part of the world,  that
>path would be about 1500 miles longer, encompassing about 4500 miles in
>width.
>
>Yes, I can see that more antenna movement will be needed from New England
>for the same signal strength. Finally a factor that favors "the rest of  us"!

 From New England, Europe subtends approximately 40 degrees of 
azimuth (35 deg (TF) to 74 deg (ZB) from Boston). There may be some 
differences in opinion over how much additional coverage is necessary 
to not exclude adjacent areas in Central Asia, N. Africa and the 
Middle East, but it's difficult to see too narrow of a beamwidth 
becoming a concern, even from New England, except perhaps for monster 
Yagis (that 7-el 10m M2 on the 44' boom still has an HPBW of 43 degrees).

Of course, putting a 40 degree wide pattern onto a 40 degree wide 
target does place a premium on accurate alignment, particularly for a 
fixed stack... which would include finding True North ;-)

A trade study of going from 4-el to 7-el and whether the ~2 dB of 
additional peak gain compensates for the ~10 degree reduction in HPBW 
can be evaluated using a tool like VOAAREA to generate coverage maps.

The difficulty in making such a comparison lies in having confidence 
that the system models being compared (the antennas in a stack over 
real terrain) are more accurate than the expected 2 dB difference 
from the unit antennas.

73,
Mike K1MK

Michael Keane K1MK
k1mk at alum.mit.edu