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From: karn@petrus.UUCP (Phil R. Karn)
Newsgroups: net.ham-radio
Subject: Re: .95 multiple factor for dipoles.....
Message-ID: <635@petrus.UUCP>
Date: Thu, 10-Oct-85 21:54:11 EDT
Article-I.D.: petrus.635
Posted: Thu Oct 10 21:54:11 1985
Date-Received: Sat, 12-Oct-85 21:22:52 EDT
References: <3220@teklabs.UUCP> <196@sri-unix.ARPA>
Organization: Bell Communications Research, Inc
Lines: 14

> The .95 factor is for what is sometimes called 'end effect'.  There
> are capacitive effects seen at the ends of the dipole that make it
> seem electrically longer than it is.  The .95 is a correction for
> that, so that it will come out to the right frequency.

The speed of light in air is neglegibly smaller than the speed of light in
vacuum. Besides capacitance seen at the ends, dipoles are made from wire
with finite diameter and this also has the effect of lengthening the dipole
electrically.  This effect is usually small at HF, but can be pretty
significant at VHF and above. It also affects the feedpoint impedance.

See the 1985 ARRL Handbook, page 17-3.

Phil