[OZAPRS] 2M 1/4 Wave antenna

[Marcus B]

On 14/01/07, Damien Gardner Jnr <rendrag at rendrag.net> wrote:
> ----- Original Message -----
> From: "Andrew Rich" <vk4tec at tech-software.net>
> > Searched for ages on google, looking for a 1/4 wave vhf calculation
for
> > 145.825 MHz
> > I remember that the 45 degree radials had to be a ratio longer or
shorter
> > than the vertical element.
> > 1/4 Wave antenna = 51.43 cm
>
> It's been years since I built a 1/4 wave antenna, and a mate has my RSGB
> antenna book at the moment, but I always used to take 5% off the
calculated
> length of the antenna.. I think for a bit of impedance matching, though
it's
> been WAY too long to say for sure :) I do remember that the radials were
> exactly 1/4 wave, and by adjusting the down-angle on them, you could
tune
> the 1/4 wave to more closely match your 50 ohm coax..? (nominal on a 1/4
> antenna is 37 ohm or something iirc?)
>
> Google seems to actually be suprisingly thin on 1/4 wave antenna info..
> Really gotta get my RSGB back :)

Yeah, I should look that up while I've got your RSGB book here

An exact 1/4 wave matches 36 Ohms, exactly half a dipole, and if I
remember correctly (it isn't in the RSGB handbook), freq / 72 (roughly
95% of a quaterwave) can be used without a large elaborate
groundplane.

But back to the handbook, it says to make a 50 Ohm match, to make the
antenna length longer than usual, then get out the SWR meter, not very
scientific for the RSGB handbook, but it does make sense in a way.

> Cheers,
>
> Damien
> --
> Damien Gardner Jnr
> VK2TDG/VK2DGJ. Dip EE. StudIEAust
> Home: rendrag at rendrag.net -  http://www.rendrag.net/
> Play: vk2tdg at pinegap.net  -  http://pinegap.net/
> --
> We rode on the winds of the rising storm,
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-- 
VK3TST
-- "People aren't stupid. Usually." -- jd
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