I did some quick NEC-2 simulations to determine the gain and take-off angle
of K9LTN's impressive array. Not knowing his exact dimensions, I used 45'
vertical spacing and 55' horizontal spacing, with the top antennas at 220'
elevation. In free space the gain is 14dbd and over average soil the gain
is 21.4 dbi with a take-off angle of 5 degrees. Of course, this assumes
flat ground and his surrounding terrain might change that. If the
surrounding terrain slopes uphill, he might have a higher take-off angle.
While a 5 degree take-off angle might seem too low for many contacts, I
understand that he can control both azimuth and elevation of the array.
With a single yagi, elevation control doesn't buy much, but when you stack
antennas it does. I ran simulations and at 20 degrees elevation the gain is
17.3 dbi at a take-off angle of 23 degrees. At 40 degrees elevation the
gain is 16.3 dbi at a take-off angle of 40 degrees. Below 20 degrees
elevation, the take-off angle is not well defined, but increases at angles
above 5 degrees. As the elevation angle is increased, the ground gain
disappears, but the resulting gain is still very good. It looks to me like
he'll be able to pick the elevation that works best for any contact.
Now for the really interesting question.: will he have enough gain to hear
his echo off the moon at moonrise? At 1500W and taking into account ground
gain, his ERP will be 207 KW.
Clay
> agreed... no disrespect to this guy but this is WAY too high (if
> the top is at 220' as the cover page shows). Had he placed it so
> the bottom antenna was at say 45 - 55' then it would have been a
> killer array... but as is it will not perform up to its
> potential a good share of the time. Radiation angle is the key -
> not gain (although having both works extremely well). When the
> angle is right however nothing should beat it for the most part.
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