. 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!

Yeah, maybe I should just try to get some assistance with an swr meter
rather than endlessly screwing around, wondering how much I'm off resonance,
and all the stress associated with all of that. Maybe, if nothing else, the
shop where I'm buying all my gear might have one.
In any case, thanks for all the advice --- I'm pretty clear on whats what,
now.

--
73
Tom H
VA7FAB

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

On Wed, 16 Mar 2005 22:17:47 GMT, "tom" wrote:

Yeah, maybe I should just try to get some assistance with an swr meter
rather than endlessly screwing around, wondering how much I'm off resonance,
and all the stress associated with all of that. Maybe, if nothing else, the
shop where I'm buying all my gear might have one.

If not, http://www.mfjenterprises.com has vhf swr meters in the 35
dollars u.s. range and up. You'll need one eventually...

bob
k5qwg


In any case, thanks for all the advice --- I'm pretty clear on whats what,
now.

They don't cover 2m, I checked.

--
73
Tom H
VA7FAB

Now that's a good idea --- I'll just have to make sure I don't jab anyones
eyes out on the subway (I'm car-less in Canada). I'm trying to imagine just
how bulky it will be, hmmm --- I should be able to manage it, I think.

--
73
Tom H
VA7FAB

On Thu, 17 Mar 2005 02:52:07 GMT, "tom" wrote:

They don't cover 2m, I checked.

You didn't check far enough. The MFJ-812B covers 2-meters and 220.
It lists for $34.95.
http://www.mfjenterprises.com/produc...rodid=MFJ-812B

Dick

You're right --- I only looked at that other site. I'll definitely shop
around for one, but even if I can find one, it'll be $70 with taxes, in
canadian dollars, and it isn't likely that I'll be able to find to begin
with up here, but what the hell --- now I know that there relatively
inexpensive meters I'm further ahead than I was before I knew about them. I
thought they were all at least $150 and up. Thanks.

--
73
Tom H
VA7FAB

tom wrote:
Thanks, that's usefull info --- but what about the swr issue? If a half
wave dipole is tuned to a certain frequency and has an swr of 1.05, say, for
the swr to rise to 2 (at VHF wavelengths) you have to go roughly 6mhz up or
5mhz down from that tuned frequency. The 2m band is only 4mhz wide in
total, anyway, so if you measure carefully, are you risking damage to the
rig (also assuming the rig has no swr protective circuitry) if you don't
check the swr with a swr meter? I don't have one, that's why I'm asking.

Hello, tom. I may be coming in to the discussion a little late.

My IC-V8000 and IC-2720 both have SWR protection circuitry that folds
back the power output if the SWR is too high. The '8000 folds back to
25 Watts and the '2720 goes to 15 on both bands.

If you want the operator's manual for your pending IC-2200 you can
download it from either www.icomamerica.com or www.icom.co.jp (and
probably Icom Canada's web site too, though my first stab at the name
didn't find the site -- icomcanada.com maybe?) and read all about its
features before you get the radio in your hands. I wouldn't be at all
surprised to find it'll fold back to a usable power level if the antenna
is less than perfect.

HTH