May 18th 04, 03:17 PM
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On 18 May 2004 06:19:50 -0700, (Brian Kelly) wrote:
Then howcum my 5/8 wave mag mount 2m mobile antenna very significantly
outperforms the 1/4 wave mag mount antenna I used to use? Same ground
condx, same power, same feeder length, same vehicle, etc. I suspect
it's in the differences in the TO angles.
My previous response was for a ground plan antenna mounted above
ground and you are addressing a mobile installation. They are
different.
I've done modeling of 1/4,1/2 and 5/8-wave whips using several wire
grid models for vehicles (small and mid-sized car, small pickup truck
and a SUV). I found that the vehicle's size, shape and whip location
plays a major part in performance.
I also noted, on the average, the 5/8 produce a slight gain over all,
but it was possible to find azimuth directions that a 5/8-wave would
produced almost 3 db gain over itself - depending what vehicle it was
mounted on.
The most outstanding feature I saw was a 5/8-wave whip azimuth pattern
was less influenced by the vehicle geometry.
The operation is more like a lop-sided dipole with the vehicle body
being on leg.
I don't feel you can accurately predict how a the whips will perform
on a vehicle based upon operation on another vehicle - unless both
vehicles and the antenna locations are the same.
I should add for all models the whips where placed top-dead-center of
the vehicle's roof.
73,
Danny, K6MHE
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