Effective grounding in an apartment
Derek Osborne
I live on the eight floor of an 18 story building. There is a chance
that I will gain an antenna presence on the roof :<). I will need a
good ground. I have three prong outlets and central heating in the shack
but to reach the nearest cold water pipe would require some forty feet
of wire. With the three prong outlet there is about three ohms of
resistance between the common and both the plumbing and the heating pipe
as opposed to about 100 ohms between the socket's ground plug and the
plumbing.
Can I use the central heating pipe as a reliable rf or dc ground?
Can I rely on the three prong plug for a dc ground (or the heating pipe
as it seemed to be grounded to the buildings plumbing) and run quarter
wavelength radials from a ground bus?
Is there any point to making the 40 ft connection to a cold water pipe?
Might it be worthwhile investing in an artificial ground tuner to use in
conjunction with the long earth (pipe) ground wire?
Thanks for any thoughts on the matter
Derek
George T. Baker
>
> Hello
> I live on the eight floor of an 18 story building. There is a chance
> that I will gain an antenna presence on the roof :<). I will need a
> good ground.
That is very likely not at all the case, Derek.
If your antenna is a dipole or other balanced structure, properly fed
with coax and a suitable balun at the antenna end, then there is no
reason whatsoever that you need a "good" ground. BTW, why would one ever
want any other kind? ;^)
You ground things in the shack for 60-Hz power protection and for
lightning protection. No other reason, if the antenna system is designed,
installed and operating properly. If not, then trying to "ground" the
station is a pointless bandaid exercise.
Getting rid of the proverbial "rf in the shack" is very seldom
accomplished by installing the equally proverbial "good ground." You hear
a lot of tales about that, but usually what happens is that some other
problem is taken care of in the course of installing that "good ground."
No, you keep rf out of the shack to begin with - that is the solution.
If the building is properly wired, then your 60-Hz grounding issue is
taken care of by the safety ground connection made with every item that
you plug into the wall socket.
That high up in a large building, with an antenna on the roof, there is
an issue about lightning protection. For that one, you need to consult
the building engineering folks who are ultimately responsible for
protecting the structure and its occupants from lightning damage. They
may well insist that you install various lightning protective measures
with your antenna, such as connecting the braid of the coax to a central
building lightning protection system, etc. They may well reexamine the
situation of your having an antenna up there and just decide that the
risk/expense is not worth the trouble to them.
On the other hand, I strongly suspect that the building has no lightning
protection as such and that anyone you ask about it will return a blank
stare. So, use your head and if you see an opportunity to connect the
coax braid to some metal aspect of the building structure, that probably
can't hurt anything.
But, you could still be liable for any subsequent damages.
I am not trying to be too negative on this issue, but when you put an
antenna on the roof of a public building, it CAN be involved in lightning
events and there COULD be damage, etc. So, you are at risk. The best of
all possible worlds is to have a waiver from the building operators
relieving you of all responsibility. Next best, I suppose, would be some
sort of insurance coverage.
Back to my original point: done right - and why do it any other way? -
the antenna system will not require any "ground" of the shack equipment;
the powerline grounding situation is covered if each item of equipment
you use and plug in is equipped with a code-required safety ground
conductor and the building is wired to code; and lightning protection is
an open issue that is highly unlikely to be dealt with by you trying some
sort of ad hoc "good ground" at the shack.
Good luck and keep us posted on what you do and how you make out! ;^)
72/73, George AMA 98452 R/C since 1964
Amateur Radio W5YR, in the 53rd year and it just keeps getting better!
AutoPOWER Systems, Fairview, TX (30 mi NE Dallas) Collin County
QRP-L QRP-ARCI FISTS NORCAL ZOMBIE ARS 10-X 33.2 N 96.6 W EM13RE
William F. Hagen
is better than no ground, your chassis will be the ground, if you dont
connect to anything else, and the power cord to the socket will provide
a path to ground ie the plug. they all will work, will be hot, will
distort radiation pattern somewhat (how much is somewhat!?) and wont be
as good as thick braid to a copper rod pounded in to salty marsh just
underneath your rig.
Derek Osborne wrote:
>
> Hello
> I live on the eight floor of an 18 story building. There is a chance
> that I will gain an antenna presence on the roof :<). I will need a
> good ground. I have three prong outlets and central heating in the shack
> but to reach the nearest cold water pipe would require some forty feet
> of wire. With the three prong outlet there is about three ohms of
> resistance between the common and both the plumbing and the heating pipe
> as opposed to about 100 ohms between the socket's ground plug and the
> plumbing.
>
> Can I use the central heating pipe as a reliable rf or dc ground?
> Can I rely on the three prong plug for a dc ground (or the heating pipe
> as it seemed to be grounded to the buildings plumbing) and run quarter
> wavelength radials from a ground bus?
> Is there any point to making the 40 ft connection to a cold water pipe?
>
> Might it be worthwhile investing in an artificial ground tuner to use in
> conjunction with the long earth (pipe) ground wire?
>
> Thanks for any thoughts on the matter
> Derek
--
Please remove the word 'NOREPLY' from the email address, sorry for the
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BarryG
George T. Baker <w5...@swbell.net> wrote in message
news:379B430C...@swbell.net...
> You ground things in the shack for 60-Hz power protection and for
I'm no expert, but sure seems like RF and data circuits/cables often need
shielding to prevent RFI and shielding depends on a good RF ground for
effectiveness . . .
73,
Barry N1EU
Richard Harrison
installation of a balanced antenna on the roof. If some salient metal
structure connected with the building is already there, you may be able
to keep your antenna well below this structure and let its "cone of
protection" keep lightning away from your antenna. It`s not the best for
antenna performance perhaps, but may be better than no performance.
Best regards, Richard Harrison, KB5WZI
Gary Coffman
>Derek Osborne wrote:
>>
>> Hello
>> I live on the eight floor of an 18 story building. There is a chance
>> that I will gain an antenna presence on the roof :<). I will need a
>> good ground.
>
>That is very likely not at all the case, Derek.
>
>If your antenna is a dipole or other balanced structure, properly fed
>with coax and a suitable balun at the antenna end, then there is no
>reason whatsoever that you need a "good" ground. BTW, why would one ever
>want any other kind? ;^)
>
>installed and operating properly. If not, then trying to "ground" the
>station is a pointless bandaid exercise.
Very well said, George. I couldn't have put it better myself.
Gary
Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
Gary Coffman
>George T. Baker <w5...@swbell.net> wrote in message
>news:379B430C...@swbell.net...
>> You ground things in the shack for 60-Hz power protection and for
>
>I'm no expert, but sure seems like RF and data circuits/cables often need
>shielding to prevent RFI and shielding depends on a good RF ground for
>effectiveness . . .
>
>73,
>Barry N1EU
No it doesn't. Shielding forms a Faraday cage around circuits or wiring.
The only requirements are that the shielding be sufficiently conductive,
and totally enclose what is being shielded. No grounds are required,
and typically no grounds are wanted because they can force ground
loop currents in the shielding. That can then induce hum and noise
into the protected wiring. One of the biggest problems when dealing
with shielding is dealing with ground loops caused by requirements
to electrically ground equipment. If everything can float above ground,
the job of shielding becomes much easier.
Dennis C. O'Connor
I have solved several cases of severe TVI/RFI for guys operating from
apartments by using a tuned counterpoise as an RF ground, ala. the MFJ unit
you mentioned... However, I always just use a 1/4 wave piece of wire as the
rf-ground/counterpoise
You want the radio and all accessories to sit on a metal plate, this can be
roof flashing, copper window screen, etc... Use this as the tie point for
everything to ground to, including your electric outlet neutral... Given the
cost of the MFJ unit, I would simply cut individual 1/4 wave lengths of
wire, one for each band you operate, route them around the outside walls of
the room/shack, or under the carpet, or hang out the window, etc., as best
you can and connect them to the metal plate under the radio...
GL ... Denny
Bob Lewis
it does have to be returned to the signal common. Otherwise it will
capacitivly couple to the inner conductors. Try a piece of coax cable
on a receiver (with no antenna connected). When the shield is not
connected to the receiver chassis it picks up signals. Connect it to
the chassis and the signals go away (or at least greatly diminish).
BarryG <bgNO...@albany.net> wrote in message
news:7ng3fd$pbh$1...@news.monmouth.com...
> My dim memories of EE classes seem to recall that Faraday cages
need to be
> grounded.
>
> A quick search on the Web to check this turned up several
references to
> Faraday cages used for EMI shielding, and they always indicated
that they
> were grounded.
>
> If the cage wasn't grounded, wouldn't any field inside the cage be
> retransmitted through induction, rendering the cage useless? If
the cage is
> floating, how is the EM energy going to be dissipated?
>
> 73,
> Barry N1EU
>
>
> Gary Coffman <ke...@bellsouth.net> wrote in message
> news:37d278ea....@news.atl.bellsouth.net...
George T. Baker
to Derek re shack grounding.
72/73, George AMA 98452 R/C since 1964
Amateur Radio W5YR, in the 53rd year and it just keeps getting better!
AutoPOWER Systems, Fairview, TX (30 mi NE Dallas) Collin County
QRP-L QRP-ARCI FISTS NORCAL ZOMBIE ARS 10-X 33.2 N 96.6 W EM13RE
Gary Coffman wrote:
>
> On Sun, 25 Jul 1999 12:02:04 -0500, "George T. Baker" <w5...@swbell.net> wrote:
> >Derek Osborne wrote:
> >>
> >> Hello
> >> I live on the eight floor of an 18 story building. There is a chance
> >> that I will gain an antenna presence on the roof :<). I will need a
> >> good ground.
> ><snip>
> >
> >That is very likely not at all the case, Derek.
> >
> >If your antenna is a dipole or other balanced structure, properly fed
> >with coax and a suitable balun at the antenna end, then there is no
> >reason whatsoever that you need a "good" ground. BTW, why would one ever
> >want any other kind? ;^)
> >
> >You ground things in the shack for 60-Hz power protection and for
> >lightning protection. No other reason, if the antenna system is designed,
> >installed and operating properly. If not, then trying to "ground" the
> >station is a pointless bandaid exercise.
>
> Very well said, George. I couldn't have put it better myself.
>
George T. Baker
use as a "driven ground" to place the station equipment near zero r-f
potential functions only because it is in the induction field of the
antenna and thus has power induced in it. The result is that current
flows in the wire and so it radiates just as any other portion of the
antenna system does.
Thus, one must be very careful to (1) insulate the "far" end of the wire
to prevent damage from the possibly large r-f voltage that can be
developed there and (2) avoid placing the wire near other equipment or
systems that could be susceptible to RFI. It goes without saying that the
wire should be laid out pretty much in a straight line and not just
wadded up and tossed in a corner.
Driven grounds and tuned grounds a la MFJ will do the job of driving the
station common to near zero r-f voltage, but they are not a cure-all and
they do have drawbacks that must be observed. Still ain't no free
lunches!
72/73, George AMA 98452 R/C since 1964
Amateur Radio W5YR, in the 53rd year and it just keeps getting better!
AutoPOWER Systems, Fairview, TX (30 mi NE Dallas) Collin County
QRP-L QRP-ARCI FISTS NORCAL ZOMBIE ARS 10-X 33.2 N 96.6 W EM13RE
Derek Osborne
I was thinking of using either a square of PCB on the underside of the desk or a
short length of copper tubing behind the desk as the common point. From your
experience is there a significant difference in having the plate immediately
beneath and in contact with the station i.e. power supply, transceiver, tuner,
keyer, ect. With a large monitor and noisy surge protectors though I can see
myself having a field day with copper screen :<).
For the dc ground I will wire the common to either the ground pin (most likely
because the ps is three prong and this should 'eliminate' a ground loop return
path) or neutral pin (tempting as it seems a more direct connection to the
building ground) of a three prong plug which will be plugged into the same
outlet cluster that feeds the power supply. As for the price of the MFJ someone
offered on on a swap & shop this evening for $25. Hmmm.
Derek Osborne
returning to the hobby after a 12yr absence and boy an I rusty.
I was thinking that the antenna field around any rf grounding counterpoise
located inside the shack would be sufficiently small to allow consideration only
of impedance transformation characteristics. Thanks for the wakeup call on this
one. A balanced feed system is so much preferred but I must plan for the
contingency of having just a long wire and/or a radiating feed line.
With regards some other issues that you previously raised it is no suprise that
the building (sub)management referred me to one of their lawyers before their
engineer :>) .
Derek
"George T. Baker" wrote:
> Let me add the reminder that the 1/4-wave counterpoise recommended for
> use as a "driven ground" to place the station equipment near zero r-f
> potential functions only because it is in the induction field of the
> antenna and thus has power induced in it. The result is that current
> flows in the wire and so it radiates just as any other portion of the
> antenna system does.
>
> Thus, one must be very careful to (1) insulate the "far" end of the wire
> to prevent damage from the possibly large r-f voltage that can be
> developed there and (2) avoid placing the wire near other equipment or
> systems that could be susceptible to RFI. It goes without saying that the
> wire should be laid out pretty much in a straight line and not just
> wadded up and tossed in a corner.
>
> Driven grounds and tuned grounds a la MFJ will do the job of driving the
> station common to near zero r-f voltage, but they are not a cure-all and
> they do have drawbacks that must be observed. Still ain't no free
> lunches!
>
> 72/73, George AMA 98452 R/C since 1964
> Amateur Radio W5YR, in the 53rd year and it just keeps getting better!
> AutoPOWER Systems, Fairview, TX (30 mi NE Dallas) Collin County
> QRP-L QRP-ARCI FISTS NORCAL ZOMBIE ARS 10-X 33.2 N 96.6 W EM13RE
>
Derek Osborne
There is a brick enclosed (probably wooden) water tower extending
approximately thirty feet above the roof. I plan to keep any antenna shorter
than this. The roof is ringed with a low, apparently ungrounded fence.
Derek
Dennis C. O'Connor
have to tune it for every band change... 1/4wl counterpoise wires for each band are
automatic...
All of the methods you mention will work... I have felt that having the gear sit
directly on the metal plate/screen was more effective, especially with taming
computor noise and with keeping rf out of the keyboard... It allows you to have
individual ground leads about 6 inches long, to the plate/screen from the major
items... Whatever method you choose, do ground every piece of equipment you can,
including the swr meter, which you usually have to drill for a screw as it never
occured to the manufacturers, ditto for the computor case/tower...
Do not use the neutral side of the 110 volt outlets for a ground... That is an
absolute no no in the NEC... Use only the ground pin...
Remember, that 40 foot of wire to the building plumbing is not a ground, it is an
antenna and your end of that wire will be very hot on some frequencies...
Tape the far ends of your 1/4 rf grounds so they can't spark to something
metallic...
Cheers ... Denny
Derek Osborne wrote:
> Hello Dennis
> I was thinking of using either a square of PCB on the underside of the desk or a
> short length of copper tubing behind the desk as the common point. From your
> experience is there a significant difference in having the plate immediately
> beneath and in contact with the station i.e. power supply, transceiver, tuner,
> keyer, ect. With a large monitor and noisy surge protectors though I can see
> myself having a field day with copper screen :<).
> For the dc ground I will wire the common to either the ground pin (most likely
> because the ps is three prong and this should 'eliminate' a ground loop return
> path) or neutral pin (tempting as it seems a more direct connection to the
> building ground) of a three prong plug which will be plugged into the same
> outlet cluster that feeds the power supply. As for the price of the MFJ someone
> offered on on a swap & shop this evening for $25. Hmmm.
>
Richard Harrison
There is a brick enclosed (probably wooden) water tower extending
approximately thirty feet above the roof.
You are in luck if that structure is equipped with a lightning rod,
air-terminals, or lighting at the top. Better yet, it could have some
structural steel tied into the building steel to prevent collapse, and
this steel extends to the top of the structure?
You don`t want to install lightning protection for the structure. It
would become your responsibility and liability.
Now, given this luck, "cones of protection" sometimes don`t extend as
far as advertised. So, to minimize exposure, your antenna needs to be
close to your water tower, and small. The antenna ends must not extend
too close to the end of the protective "shadow" of the water tower.