[Elecraft] RE: In Shack Radials and Ground

Don Wilhelm w3fpr at earthlink.net
Tue Jan 23 22:49:00 EST 2007 

Jim,

Actually a half wavelength run to a ground rod will produce a low impedance
at the shack end - if the ground rod is truly a good RF ground (sometimes it
is and sometimes not).  So yes, it can have a positive influence, but it
will not guarantee it (the effectiveness depends on the ground
characteristics at the grounded far end) - the half wave wire only repeats
what it has on the other end.

Yes, we agree that a proper antenna system is the ideal solution, and that
quarterwave counterpoises can help (as long as the user remembers that the
quarter wave starts at the antenna tuner or transceiver - it seems that
subtle fact is often overlooked or ignored).

73,
Don W3FPR

> -----Original Message-----
> From: JIMMY D HARRIS [mailto:ab0uk at msn.com]
> Sent: Tuesday, January 23, 2007 7:40 PM
> To: w3fpr at arrl.net; elecraft at mailman.qth.net
> Subject: RE: In Shack Radials and Ground
>
>
> 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" <w3fpr at earthlink.net>
> >Reply-To: <w3fpr at arrl.net>
> >To: "JIMMY D HARRIS" <ab0uk at msn.com>
> >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: elecraft-bounces at mailman.qth.net
> > > [mailto:elecraft-bounces at mailman.qth.net]On Behalf Of JIMMY D HARRIS
> > > Sent: Monday, January 22, 2007 10:46 PM
> > > To: w3fpr at arrl.net; elecraft at 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" <w3fpr at earthlink.net>
> > > >Reply-To: <w3fpr at arrl.net>
> > > >To: "JIMMY D HARRIS" <ab0uk at msn.com>,<elecraft at 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
> > > > >
> > > >--
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> > > >7:30 AM
> > > >
> > >
> > >
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