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In Shack Radials and Ground

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JIMMY D HARRIS

In Shack Radials and Ground

Hi folks,

Someone asked here about RF in the Shack. There were several post on the
subject. At the risk of creating controversy and subsequent flames I have
two comments.

Several replies that mentioned about making radials in the shack. To me
that only bandaids the problem. Something is amiss if an antenna system is
creating RF in the shack. Tuning out the RF with radials can cut down RF in
the shack but doesn't correct the real problem. Correcting the real problem
could increase ERP.

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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Don Wilhelm-3

RE: In Shack Radials and Ground

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
>

JIMMY D HARRIS

RE: 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" <[hidden email]>
>Reply-To: <[hidden email]>
>To: "JIMMY D HARRIS" <[hidden email]>,<[hidden email]>
>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
>

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N2TK

RE: In Shack Radials and Ground

In reply to this post by Don Wilhelm-3

Don,
I concur with what you are saying.
At one installation the equipment was quite a distance from the ground rod.
I installed a good DC ground. But there was still RF floating around. What I
did was parallel insulated wires between the amp and the ground rod. Each
wire was longer than the next. If I remember each of the insulated wires was
a quarter wave on 15, 20 and 40M. RF problems disappeared.
73,
N2TK, Tony

PS - K2 #3481 is ready to take back to WP2Z the end of February for ARRL SSB
Test.

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of Don Wilhelm
Sent: Monday, January 22, 2007 10:27 PM
To: JIMMY D HARRIS; [hidden email]
Subject: RE: [Elecraft] In Shack Radials and Ground

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

--
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

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