. A couple other guys who know what they're talking about are also
recommending that same arrangement. 50 ohms on the cable and 50 ohms on the
antenna --- perfect. No need for a matching device, I like it. But aren't
dipole-like configurations supposed to present 73 ohms of load? Why is a
1/4 wave groundplane only 50 ohms?

The simplest ground-plane-style antenna has its radials sticking out
sideways. It's a monopole. The actual radiator is only half as long
as a dipole, and thus has only half as much radiation resistance, and
the feedpoint impedance is only half as much as that of a dipole.
It's on the order of 35 ohms or so.

If you bend the radials until they point straight down, you've got a
center-fed dipole with the feedline running up the center. Feedpoint
impedance is somewhere around 70 ohms.

Feedpoint resistance of anywhere from 35 to 70 ohms are available via
the obvious compromise - just bend the radials down less (for lower
resistances) or more (for higher resistances).

In most installations, radials bent downwards at an angle of about 45
degrees result in a 50-ohm resonant feedpoint resistance.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

OK, I'm sold --- a groundplane vertical it will be. In fact, I think I'll
go ahead and make it ahead of time so it's already set up and ready to go
when I get the IC2200H.
Thanks again for all the help ...

--
73
Tom H
VA7FAB

On Wed, 16 Mar 2005 22:44:41 GMT, "tom" wrote:

OK, I'm sold --- a groundplane vertical it will be. In fact, I think I'll
go ahead and make it ahead of time so it's already set up and ready to go
when I get the IC2200H.
Thanks again for all the help ...


Seeing that you are getting the rig in the future, you might want to
take your antenna to the shop when you pick up your rig. They will
probably be glad to see that it is tuned for your radio so you don't
ruin it.


--
73 for now
Buck
N4PGW

Check with your local club and see if someone has an swr meter you can
borrow. Most clubs are happy to help out.


Jeff
KBØGVI

I just got the rig all set up a few minutes ago with a vertical
groundplane --- a design I chose because it obviated the need for any kind
of matching due to it's intrinsic, unbalanced 50 ohms impedance. Works like
a charm too, thanks to everyone for all the excellent advice, its very much
appreciated.

--
73
Tom
VA7FAB
Skype Name:
va7fab_tom_in_vancouver