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Grounding question - this is wierd.....



 
 
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  #1  
Old August 20th 03, 03:31 PM
John Passaneau
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Default Grounding question - this is wierd.....

Hi Ken:

Sound to me like a classic RF in the shack problem. With the two mag-mount
antenna that close to the rest of the station RF pick up seems like a sure
thing. When you move your bit of ground braid around your changing the
electrical length outside of the coax. Any wire over a few inches long is
not a RF ground.


--
John Passaneau
Penn State University, State College Pa.
W3JXP


"Ken Bessler" wrote in message
...
I'm trying to understand a grounding situation at myt ststion. Here
is the station layout:

Pyramid Phase III 25 amp power supply feeding power to all
devices. First there is the radio - a Yaesu FT817. The antenna
output from this goes to a 2 position antenna switch. One side
of the switch feeds directly to a high perormance 2m/440 dual
band mag mount antenna on my A/C unit. The other side goes
to a MFJ 1040B rf preselector (also powered by the Pyramid).
The preselector has 2 antenna outputs - one goes to a Rat shack
11 meter "high performance" mag mount antenna (tuned for 10m)
also on my A/C unit. The other output goes to a LDG Z11
autotuner. The output from the tuner goes to a 34' long inverted
V antenna outside my window (I'm on the 3rd floor).

All these devices share a common ground through either the
coax shield or DC power ground or both. I have yet to install
a proper station ground for the whole setup and I don't know
if the power supply is grounded properly at the 115v ac outlet.

There - now that that is said, here is the problem:

When tuned on any band, my SWR gets better if I touch the
case of the tuner. I then installed a 1/4" braid from the tuner's
chassis screw to the ground lug on the antenna switch and that
solved the problem. I moved the braid from the antenna switch
to the case of the MFJ 1040B and the same thing happened
but not nearly as good as the effect I got when hooked to the
antenna switch.

I thought the coax sheild was a good ground path - how
could installing a ground line between the tuner and the
switch help? All chassis's are metal except for the sides of
the MFJ 1040B preselector. All patch coax cables have been
swapped out with others with no changes seen. The system
as a whole seems to operate well - on 10 m the mag mount
works best. Below that the inverted V works better. Although
the Z11 can't autotune below 5 mhz, I can manually tune and
get a good SWR down to 1.8 mhz with the Z11 in manual mode.

Grounding will be easy when I get around to it - I have
baseboard hot water radiators that I can ground to.

Any ideas, folks?

72's de Ken KG0WX






  #2  
Old August 20th 03, 04:47 PM
Dave Shrader
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Posts: n/a
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I designing RF grounds for USAF systems the coax braid was NEVER, NEVER,
used as part of the ground system!!!

I agree with one of the other POSTS regarding RF in shack.

DD, W1MCE
+ + +
Ken Bessler wrote:

I'm trying to understand a grounding situation at myt ststion. Here
is the station layout:

Pyramid Phase III 25 amp power supply feeding power to all
devices. First there is the radio - a Yaesu FT817. The antenna
output from this goes to a 2 position antenna switch. One side
of the switch feeds directly to a high perormance 2m/440 dual
band mag mount antenna on my A/C unit. The other side goes
to a MFJ 1040B rf preselector (also powered by the Pyramid).
The preselector has 2 antenna outputs - one goes to a Rat shack
11 meter "high performance" mag mount antenna (tuned for 10m)
also on my A/C unit. The other output goes to a LDG Z11
autotuner. The output from the tuner goes to a 34' long inverted
V antenna outside my window (I'm on the 3rd floor).

All these devices share a common ground through either the
coax shield or DC power ground or both. I have yet to install
a proper station ground for the whole setup and I don't know
if the power supply is grounded properly at the 115v ac outlet.

There - now that that is said, here is the problem:

When tuned on any band, my SWR gets better if I touch the
case of the tuner. I then installed a 1/4" braid from the tuner's
chassis screw to the ground lug on the antenna switch and that
solved the problem. I moved the braid from the antenna switch
to the case of the MFJ 1040B and the same thing happened
but not nearly as good as the effect I got when hooked to the
antenna switch.

I thought the coax sheild was a good ground path - how
could installing a ground line between the tuner and the
switch help? All chassis's are metal except for the sides of
the MFJ 1040B preselector. All patch coax cables have been
swapped out with others with no changes seen. The system
as a whole seems to operate well - on 10 m the mag mount
works best. Below that the inverted V works better. Although
the Z11 can't autotune below 5 mhz, I can manually tune and
get a good SWR down to 1.8 mhz with the Z11 in manual mode.

Grounding will be easy when I get around to it - I have
baseboard hot water radiators that I can ground to.

Any ideas, folks?

72's de Ken KG0WX





  #3  
Old August 20th 03, 06:54 PM
Richard Clark
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Posts: n/a
Default

On Wed, 20 Aug 2003 11:29:25 -0600, "Ken Bessler"
wrote:


In other words, don't rely on the sheild to provide a ground path but
use a flat braid that is not part of an active transmission line?


Hi Ken,

Yes and no.

It has been offered, and your experience confirms, that there is RF on
the coax (as well as RF "in" the coax). The solution is to inhibit
that, not try to short it to ground. You can try, certainly, and
succeed - for one band. Instead you should fix the problem by
snubbing the current at the source. Use a choke.

The second part of using coax to ground components. If you have a
wiring problem (you have one if you cannot trust your AC mains to
supply ground) that lifts one chassis level to 115VAC and that is
cured by a coax connection to another chassis safely at ground; then
guess what happens when you hold that grounded chassis and disconnect
the other's path to that ground? 115VAC through two arms and across
the chest when you twist off the connection. That would not happen if
they shared the same safety ground through proper connections.

73's
Richard Clark, KB7QHC
  #4  
Old August 21st 03, 01:05 AM
Ken Bessler
Guest
 
Posts: n/a
Default


"Owen Duffy" wrote in message
...
I urge you to check that you have an effective equipotential bond from
the shack equipment to the electrical installation earth.

Owen


Good advice - I guess I should check the outlet for proper
installation then run a braid from the electrical ground to the
copper pipe? My dad owns one of those nifty radio shack
plug in outlet testers - I think I'll borrow it. :-)

Jeez - lots of good advice on this group! Thanks again....

72's de Ken KG0WX


  #5  
Old August 21st 03, 02:51 PM
Floyd Sense
Guest
 
Posts: n/a
Default

Not braid for this application. Use solid copper #6 or larger. The
National Electrical Code specifies that all the grounds must be tied
together and how it should be done. There are many good reasons for this,
not the least of which deals with the effects of lightning. If you live in
an area where thunderstorms occur, you really need to look into the
grounding issue. Multiple isolated grounds can be far worse than none at
all! By the way, does that copper baseboard heating pipe really have a
continuous conducting path to earth ground?

K8AC



"Ken Bessler" wrote in message
...

"Owen Duffy" wrote in message
...
I urge you to check that you have an effective equipotential bond from
the shack equipment to the electrical installation earth.

Owen


Good advice - I guess I should check the outlet for proper
installation then run a braid from the electrical ground to the
copper pipe? My dad owns one of those nifty radio shack
plug in outlet testers - I think I'll borrow it. :-)

Jeez - lots of good advice on this group! Thanks again....

72's de Ken KG0WX




  #6  
Old August 24th 03, 03:27 PM
Ken Bessler
Guest
 
Posts: n/a
Default


"David Robbins" wrote in message
...

"Adam T. Cately" wrote in message
...
SNIP

I haven't read the rest of the thread, but here's something glaringly
obvious...

Grounding will be easy when I get around to it - I have
baseboard hot water radiators that I can ground to.


NEVER ground to hot water pipes - ALWAYS use the cold water pipe,
as it goes directly to the earth outside the building. The hot water
pipes are routed through the hot water heater(s) and are NOT a direct
path to ground.


first a couple of truisms:
NEVER say NEVER.
NEVER believe anyone who asserts an ALWAYS.
In the end an easy job is rarely as easy as you first thought.

That being said, NEVER rely on pipes of any kind for safety (either AC or
lightning) grounding of equipment, ALWAYS run your own wire to the proper
ground rod or electrical service connection as required by electrical

codes.

RF "grounds" are another problem. The problem here is to remember that

any
conductor more than a small fraction of a wavelength will have currents
induced in it and thus have a different voltage at one end than the other
when exposed to an HF RF field. The real aim here is two fold: First, to
provide a low resistance path for 'ground' currents back to the antenna

end
of the feedline so the currents in the feedline can be properly balanced.
Second, to keep all equipment and personel in the antenna field near the
same potential to prevent injury and reduce interference.



Ha! Great point!

I'm planning on buying a Radio Shack outlet tester (22-141, pg 238 of
the last catalog) - if it shows my outlets are configired properly, I plan
on
running a heavy insulated ground wire from the outlet to the pipe (8").

Does this sound right to you? As far as RF goes, I can touch *any*
component of the system and not see any DC current, SWR or other
changes at all when transmitting so I guess I've got a pretty good RF
ground already.

Then there is the performance issue - the solar numbers haven't been
very good for some time but yesterday I worked stations coast to
coast on 20 & 40 with 5 watts and got some impressive signal reports.
So, whatever I'm doing, it seems to be working OK.

72's all De Ken KG0WX/QRP


  #7  
Old August 24th 03, 04:43 PM
David Robbins
Guest
 
Posts: n/a
Default


"Ken Bessler" wrote in message
...

"David Robbins" wrote in message
...

"Adam T. Cately" wrote in message
...
SNIP

I haven't read the rest of the thread, but here's something

glaringly
obvious...

Grounding will be easy when I get around to it - I have
baseboard hot water radiators that I can ground to.

NEVER ground to hot water pipes - ALWAYS use the cold water pipe,
as it goes directly to the earth outside the building. The hot water
pipes are routed through the hot water heater(s) and are NOT a direct
path to ground.


first a couple of truisms:
NEVER say NEVER.
NEVER believe anyone who asserts an ALWAYS.
In the end an easy job is rarely as easy as you first thought.

That being said, NEVER rely on pipes of any kind for safety (either AC

or
lightning) grounding of equipment, ALWAYS run your own wire to the

proper
ground rod or electrical service connection as required by electrical

codes.

RF "grounds" are another problem. The problem here is to remember that

any
conductor more than a small fraction of a wavelength will have currents
induced in it and thus have a different voltage at one end than the

other
when exposed to an HF RF field. The real aim here is two fold: First,

to
provide a low resistance path for 'ground' currents back to the antenna

end
of the feedline so the currents in the feedline can be properly

balanced.
Second, to keep all equipment and personel in the antenna field near the
same potential to prevent injury and reduce interference.



Ha! Great point!

I'm planning on buying a Radio Shack outlet tester (22-141, pg 238 of
the last catalog) - if it shows my outlets are configired properly, I plan
on
running a heavy insulated ground wire from the outlet to the pipe (8").

Does this sound right to you? As far as RF goes, I can touch *any*
component of the system and not see any DC current, SWR or other
changes at all when transmitting so I guess I've got a pretty good RF
ground already.

Then there is the performance issue - the solar numbers haven't been
very good for some time but yesterday I worked stations coast to
coast on 20 & 40 with 5 watts and got some impressive signal reports.
So, whatever I'm doing, it seems to be working OK.

72's all De Ken KG0WX/QRP


tying the radiator to the electric service neutral probably won't hurt. if
the radiator is plumbed with metal pipe and is up to code they are probably
tied together somewhere else also. and its always a good idea to be sure
your outlets are wired properly, especially in older homes.

if you can touch stuff and not see any changes that probably means that you
have a low enough resistance connection back the the feedline point at the
antenna. that is where lots of people mess up, they ground the shack end of
the coax, but then connect just the center conductor to a random wire or
something like that outside. this arrangement forces the return current to
flow through ground, the shack equipment, back out the outside of the coax
and then back inside the coax to complete the circuit. this causes all
sorts of problems like the infamous rf burns from the key or mic,
interference to nearby tv, stereo, and computer equipment, etc. even
balanced lines and antennas are susceptable to this. if the antenna isn't
really balanced (say one leg is near the house the other is in the clear)
the unbalance in the return path can cause current to flow back through
wiring in the house to get back to the feedline.

with the poor solar conditions right now you are probably doing just fine,
just be sure you have a good safety ground and enjoy.



  #8  
Old August 24th 03, 05:04 PM
Reg Edwards
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NEVER ground to hot water pipes - ALWAYS use the cold water pipe,
as it goes directly to the earth outside the building. The hot water
pipes are routed through the hot water heater(s) and are NOT a direct
path to ground.

==========================

Not entirely correct.

ALWAYS use the cold water pipe.

And if you have a hot water pipe ALWAYS connect that in parallel.

Two connections in parallel ALWAYS have a lower impedance than either of
them.

Hot water, wall-mounted, central heating radiators are convenient connecting
points.

If you have a gas pipe then make it a three-some.

And of course take advantage of the electricity supply ground via the
domestic power wiring.

If there's a 14-gauge wire running from a bedroom shack, through the window,
down the outside wall, to a bunch of buried radials in the back yard then
include it with the others.

The whole system is just a bunch of random length radials and, up to a
break-even point, the more the merrier.

If any one of the principal ground connections can be broken without having
any affect on the tuner settings then you've already gone far enough.

But whatever you have there's no guarantee you will be free of RF in the
shack. RF comes in through the windows, ceiling, walls, doors and floor of
the shack direct from the high-power near-field of the antenna. And you
can't criticise the antenna - it's only doing its job.

If in a bedroom, as a last desperate resort, take up the carpet or lino and
cover the floor-boards with chicken wire. Re-lay the carpet or lino. Connect
the chicken wire from two spaced points to the terminal at the rear of the
PA which is marked "Ground".
----
Reg, G4FGQ


  #9  
Old August 24th 03, 07:53 PM
Dave Platt
Guest
 
Posts: n/a
Default

In article ,
Ken Bessler wrote:

I'm planning on buying a Radio Shack outlet tester (22-141, pg 238 of
the last catalog) - if it shows my outlets are configired properly, I plan
on running a heavy insulated ground wire from the outlet to the pipe (8").

Does this sound right to you?


I would advise _against_ doing this, for a couple of reasons.

One is that the Radio Shack tester can detect certain forms of
mis-wiring, but there's at least one which it cannot detect. This is
one in which you have a three-wire outlet, hooked up to a two-wire
power feed (one which doesn't actually have a ground), and the
installer simply wired the "neutral" and "ground" screws together at
the outlet.

To a simple static-voltage-based tester (such as the Radio Shack one
appears to be) this outlet will test out as "good" - there will be 120
volts between hot and neutral, 120 between hot and ground, and zero
between neutral and ground.

However, this sort of outlet does _not_ provide a true safety ground.
If you start drawing a large amount of current through the wire (from
this outlet or from another on the same wire), both the "neutral" and
"ground" contacts will be pulled several volts away from ground by the
I*R losses in the neutral wire. If you've got your equipment chassis
"grounded" to this outlet, the chassis will be pulled up away from
ground - this could present a shock hazard. Also, you can end up with
some portion of the power return current (back to the neutral
connector at the breaker box) flowing where you don't want it...
through your equipment chassis, your hot-water pipe, your
antenna-cable coax braid, etc.

Proper testing for a neutral/ground crossconnection may require
physical inspection of the outlet. It can, I think, also be detected
by measuring the voltage between the neutral and ground pins at an
outlet, while drawing a heavy current (e.g. a 1500-watt space heater)
through the other side of that outlet. If the outlet is wired
properly, you _should_ see at least a volt or so develop between these
two pins - if you don't, it may indicate a neutral/ground crossconnect
at that outlet.

The other reason I'd discourage wiring the power-outlet ground to your
hot-water-heater pipe, is that the National Electric Code doesn't
permit this. If a short circuit occurs somewhere on this circuit, it
would cause your water pipes to carry some of the current back to the
house ground, and this could result in a shock hazard for anyone in
contact with the pipes (e.g. somebody in a shower or tub).

As I recall, the electrical and plumbing systems really should remain
electrically isolated from one another _except_ at a single "bonding"
point. This ensures that the plumbing system cannot carry
ground-return currents, if a fault occurs in the electrical wiring.

--
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!
  #10  
Old August 25th 03, 01:41 AM
Reg Edwards
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The previous posting, of course, applies to RF grounding of the radio shack,
particularly to end-fed antennas where at some frequencies there may be
appreciable RF currents flowing from the shack down to ground via the very
uncritical arrangements previously described.

If there are any local or national regulations to be complied with regarding
the domestic power frequency safety ground then they should be complied
with. But in general such regulations, by themselves, will fall far short of
an adequate radio ground.

For example, a single safety ground rod, wherever it is located, will likely
have a resistance at all frequencies greater than 50 ohms plus the important
inductive reactance of all the wire between the shack and the rod. By all
means include the rod in the station's RF ground system but it will be found
to be amongst the ground connections which can be disconnected without
having any effect on station operation such as tuner settings.

A single rod is no better than a buried horizontal radial wire of the same
length. If a rod is the only RF ground available an endfed antenna will work
in some poor fashion, RF in the shack, etc., unless the local soil is
saturated with salt water - an unlikely condition.

To protect the family home from direct lightning strikes on the antenna then
the mast etc., is best provided with its own ground electrode system. We
have very few thunder storms in the UK. In all my years I have seen only one
lightning strike which hit the ground. So what I have done when a storm
seemed imminent (the tuner capacitor sparking over) is just disconnect the
antenna at the lead-in to the shack and toss the loose end of the wire as
far as I can along the back yard.

For antenna + mast grounding details I leave to more experienced people.
---
Reg, G4FGQ


 




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