Don,
Maybe my thinking is too simple. But here goes. I believe that we both
have indicated that quarter wavelength can eliminate RF in the shack among
other RF problems caused by less than a perfect antenna system. I believe
that we also agree that a half wavelength does not do that. Therefore, a
half wavelength ground wire has no positive influence on RF problems. That
indicates to me that I should avoid half wavelength ground runs as they have
no positive influence on RF problems. I would guess in the world of amateur
radio there are RF problems that are not recognized. Half wavelength
grounds runs do nothing to clear up those problems. Of course, the real
solution is to have an adequate antenna system. You can bet that in
commercial systems a proper antenna system is used.
Jim, AB0UK
From: "Don Wilhelm" <[EMAIL PROTECTED]>
Reply-To: <[EMAIL PROTECTED]>
To: "JIMMY D HARRIS" <[EMAIL PROTECTED]>
Subject: RE: In Shack Radials and Ground
Date: Mon, 22 Jan 2007 23:23:09 -0500
Jim,
The way I read your post was that half wave lengths of wire to the ground
rod are things to stay away from. Perhaps I mis-understood your intent -
but you did say to stay away from ground rod runs that are a half wave or a
multiple thereof, and that is the incorrect part.
Yes, the run to the ground rod can radiate - but that is not necessarily a
bad thing.
The really best place to create the RF Ground is at the antenna (or its
feedpoint), but not all folks are blessed with a controllable situation and
must resort to other 'cures' like tuned counterpoise wires.
I have no RF in the shack problems here, all my antennas have an effective
RF ground as an integral part of their design (no OCF antennas here), and I
have to suffer with a 150 foot run of coax before I get to the distribution
point going to the antenna field. It keeps the RF out of the shack, but
requires low loss coax runs.
73,
Don W3FPR
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] Behalf Of JIMMY D HARRIS
> Sent: Monday, January 22, 2007 10:46 PM
> To: [EMAIL PROTECTED]; elecraft@mailman.qth.net
> Subject: RE: [Elecraft] In Shack Radials and Ground
>
>
> Don,
>
> I'm not sure we disagree. I seems like we are both are agreeing to stay
> away from quarter wavelength ground runs (wires) and use half
> wavelength.
> That is what I intended to say. Usually ground systems are not
> effective RF
> grounds. The connecting wire may be a relatively effective
> radiator or an
> element in tuning an antenna system.
>
> Jim, AB0UK
> k2/100 S/N 4787
>
>
> >From: "Don Wilhelm" <[EMAIL PROTECTED]>
> >Reply-To: <[EMAIL PROTECTED]>
> >To: "JIMMY D HARRIS" <[EMAIL PROTECTED]>,<elecraft@mailman.qth.net>
> >Subject: RE: [Elecraft] In Shack Radials and Ground
> >Date: Mon, 22 Jan 2007 22:27:08 -0500
> >
> >Jim,
> >
> >Sorry to disagree - consider what happens on a quarterwave wire:
> It has a
> >low impedance at one end and a high impedance at the other end. Think
> >about
> >what will happen if you connect the far end of a quarter wave wire to a
> >good
> >ground (low impedance) - the other (near) end will have a high
> impedance at
> >that frequency, and will not serve as an RF ground at all (in fact
quite
> >the
> >opposite).
> >
> >A halfwave wire however can have a low impedance at each end, so
> grounding
> >the far end of a half wave wire will make the near end at a similarly
low
> >impedance.
> >
> >A grounded radial and a counterpoise wire are two different things -
the
> >counterpoise wire creates a low impedance (about 35 ohms) by nature of
> >having the far end ungrounded, whereas a grounded (or buried)
> radial forms
> >a
> >screen or reflector - yes, the counterpoise will radiate because
> it becomes
> >a part of the antenna system. The counterpoise controls the radiation
> >instead of having it wander willy-nilly around the shack and other
places
> >where it should not be present.
> >
> >I do understand that this is not intuitive - we have to think in terms
of
> >antenna theory when dealing with RF grounds - what works fine at
> DC and low
> >frequency AC does not necessarily work at RF.
> >
> >Ground rods can be a good RF ground, but the wire connecting the
> ground rod
> >to the shack may not behave as expected - a 16 foot connection to the
> >ground
> >rod will present a high impedance to 14 MHz RF at the shack end - but
> >should
> >be a good RF ground for 10 meters since it is a halfwavelength away
from
> >the
> >low impedance ground rod.
> >
> >73,
> >Don W3FPR
> >
> > > -----Original Message-----
> > >
> > > There was mention about ground rods not being a good RF
> ground. For the
> > > most part I agree with that. However, the wiring to the
> ground rod is
> >in
> > > fact a radial that is some part of a wavelength long. As we know
> >quarter
> > > wavelength radials can tune out RF. By the same token other
> fraction
> >of
> > > wavelength ground runs (radials) can create RF in the shack
> when used in
> > > conjunction with a poorly designed antenna system. Stay away from
> >ground
> > > runs that are halfwave wavelength (or near) or multiples thereof of
> > > frequencies your antenna system is designed for.
> > >
> > > 'nough said......
> > >
> > > Jim, AB0UK
> > > K2/100 S/N 4787
> > >
> >--
> >No virus found in this outgoing message.
> >Checked by AVG Free Edition.
> >Version: 7.5.432 / Virus Database: 268.17.4/644 - Release Date:
1/22/2007
> >7:30 AM
> >
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft@mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.432 / Virus Database: 268.17.4/644 - Release Date:
> 1/22/2007 7:30 AM
>
--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.432 / Virus Database: 268.17.4/644 - Release Date: 1/22/2007
7:30 AM
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
