Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Sun, 24 Aug 2003 01:45:03 -0400
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From: "Charles R. Patton" <charles.r.patton@ieee.org>
Reply-To:  charles.r.patton@ieee.org
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Subject: Re: [LML] Antenna Performance Demo
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Brent Regan wrote:

> There was a very interesting demo at the RAMI both at OSH. The demo 
> consisted of a standard, belly mounted, COM antenna on a pole, and 
> connected to an analyzer. The point of the demo was to show the 
> difference in VSR (a measure of an antennas efficiency, lower numbers 
> are good with 1.0 being as good as it can get) 

Brent,
I'm sorry, but you have to be careful about making this statement. The 
only thing that a low VSWR guarantees is maximum power transfer from the 
source if it’s impedance is that of the VSWR measuring device. It 
absolutely does not guarantee radiation efficiency. It is that in most 
circumstances with similar style antennas, the radiation efficiency of 
the antenna is similar, therefore more power in is more power radiated.

Without doing antenna range type measurements, I am concerned with using 
carbon fiber as your ground plane. There is the real possibility that 
you can get a match to the cable, and dissipate a significant amount of 
RF in the resistive carbon. You could have good VSWR, but lowered 
radiation efficiency. This would also translate to a lower receiving 
antenna efficiency too.

Charles R. Patton
LNC2 360JM