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> From: sbest@cushcraft.com
> To: towertalk@contesting.com; jreid@aloha.net
> Subject: Re[2]: [TowerTalk] Steve's antenna study (GAIN)
To: <towertalk@contesting.com>
> Date: Tuesday, July 21, 1998 12:22 PM
OK here.
> Directivity of an antenna does come from antenna geometry. If an
> antenna is 100% efficient it will have a gain equal to its
> directivity. Gain is simply the antenna directivity * efficiency.
> Reductions in efficiency come from losses within the antenna
> structure, losses within any feedpoint matching components
You might want to consider wording this a bit more careful. It might be
misunderstood and incorrectly support incorrect impressions line efficiency
is directly related to VSWR.
>AND high
> VSWR. Increased VSWR reduces power delivered to an antenna because
of
> the reflections created at the antenna . This has the effect of
> reducing gain since the total power delivered to the antenna is less
> than the power incident at its input terminal.
The effect of "reflected waves" or mismatches on the feedline and antenna
system is only that apparent power handled by the feedline increases. If
matched feedline loss is very low, the SWR can be very high and feedline
and antenna efficiency nearly 100% even in a mismatched condition.
I operate lines with SWR exceeding 20 to one, and don't even give up a
fraction of a dB doing so.
73 Tom
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