--- On Wed, 5/6/09, Joe Subich, W4TV <li...@subich.com> wrote:
> From: Joe Subich, W4TV <li...@subich.com>
> Subject: Re: [Elecraft] Driveway Distortion Demolition Derby
> To: "'Ron D'Eau Claire'" <r...@cobi.biz>, elecraft@mailman.qth.net
> Date: Wednesday, May 6, 2009, 10:30 AM
> > Wes is quite right for the USA at least, and to make it
> easy
> > on us the FCC defines a 1/2 wave dipole as a "0
> dBd" antenna
> > even though most 1/2 wave antennas show some gain over
> isotropic.
>
> Is that a dipole in free space or a dipole over ground?
The rules seem to be mute on this, but I imagine the idea is a theoretical,
free-space dipole.
>
> A dipole over ground will generally have a peak gain of
> 8.3 to 8.5 dBi depending on the dipole mounting height and
> the angle (elevation) at which the measurement is made.
>
> Given the efficiency of a mobile whip, transmitter output
> power could probably be 500 watts before the ERP would
> be equivalent to 50 watts to a dipole with 8.5 dBi gain.
I did a quick EZNEC calculation of an 2.4 M tall whip with 20 ohm ground loss
(not unreasonable and likely conservative) and the "gain" is about -11 dBd.
Wes N7WS
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