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Re: [VHFcontesting] A question of altitude

To: Dan Evans <dan.evans@insightbb.com>, vhfcontesting@contesting.com
Subject: Re: [VHFcontesting] A question of altitude
From: Tom Carney <tomc@carneysugai.com>
Date: Thu, 06 Mar 2008 17:34:01 -0800
List-post: <vhfcontesting@contesting.com">mailto:vhfcontesting@contesting.com>
Dan Evans wrote:
> With antennas that low, I think the biggest influence is the vehicle and 
> not the take off angle.   It may be completely wrong, but I always 
> pictured it as the vehicle in the near field coupling with the antenna, 
> and creating considerable loss.
> 
> At some "minimum" point above the vehicle, this loss is reduced to 
> negligible level.  From Jon's, W0ZQ /R, data, it would seem that height 
> for 6 meters would be around 21 feet.  Actual numbers would depend on 
> the band involved, and the antenna.
> 
> All of this is my opinion based on my experience and anecdotal 
> evidence.  I'm a Rover, not a scientist:-)  Your points per mile may vary!
> 
> 73
> Dan

I've had a somewhat similar problem with the vehicle being in the field 
of the 6M ant.  When I first started roving, I mounted the 6M beam at 
the bottom of my "stack".  This put it at only 10 ft above ground and 
about four feet above the vehicle.

I experienced a weird bunch of Rf feedback/SWR problems.  Finally traced 
it to the short distance between the 6M beam and the vehicle.  With the 
beam pointed over the Jeep, the SWR would go above 2:1 and I experienced 
RF feedback.

Now I mount the 6M ant on top of the stack.  It still only at 15 ft and 
I can see some interaction when I turn over the vehicle but it's minimal.

73,

Tom K6EU/r


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