Danny Richardson wrote in
:

On Mon, 30 Jul 2007 13:40:27 +0000 (UTC), John Passaneau
wrote:

I want to follow on what some of the other have said.
First to only reason to have an RF ground in you shack is if you are
going to use an antenna that brings part of the antenna that is
supposed to radiate RF into the shack, as an example, a long wire
antenna. Dipoles, beams and verticals that are feed with coax do not
need RF grounds in the shack

Not true. Feeding an antenna with coax does not remove the need for a
station ground and here's why:

http://k6mhe.com/sub/BlancedFeedLine.pdf


Danny,K6MHE


Hi:
Interesting web site, but what I meant to say and didn’t do well, is
that if the antenna is installed properly and feed properly with coax
and a balun or open wire line that is properly balanced, there will
never be RF problems that an RF ground in the shack will solve. I had a
problem with 80 meters at high power turning on my furnace. It was
caused by the thermostat line being near resonate at 80 meters. All the
RF grounds in the world would not have helped that, a clamp on ferrite
choke did. It is very hard to get a RF ground in a second floor room.
The idea that one or more ground rods or ground rods and radials outside
with a length of wire running up to a second floor shack will be
anything close to an RF ground at any Ham frequency is just plan wrong.
How ever a lighting ground is a necessity and ground rods work quite
well for that.

John Passaneau W3JXP

On Mon, 30 Jul 2007 12:08:33 -0700, wrote:

On Jul 30, 10:04 am, Danny Richardson wrote:


Not true. Feeding an antenna with coax does not remove the need for a
station ground and here's why:

http://k6mhe.com/sub/BlancedFeedLine.pdf

Danny,K6MHE

The coax has nothing to do with it. Whether or not the antenna is
complete will be a much more deciding factor.
But still, I see nothing in the pdf that would imply a ground
is needed for feeding such an antenna, coax fed or not.
Only decoupling of the feedline is needed. Not a shack ground.
Why would one "need" a station ground in that case, assuming
the feedline is decoupled?
How would adding a station ground improve operation of a "complete"
antenna that was not well decoupled?
Myself, I would consider that a "bandaid" approach to the common
mode problem. A ground can hide problems in some cases, but
it never actually fixes anything. Common mode problems should
never be "cured" by station "RF" grounding.
MK



May things you say are correct, but remember that a balun/choke does
not totally choke off (eliminate) common mode current on the
transmission line (particularly a multi-band antenna system) and a
good station ground can provide additional reduction RFI problems.

For example here at my station where I have a half way decent single
point RF grounding system. If I remove just my ground connection to my
tuner - leaving everything else intact - and turn on my old CRT
computer monitor I have over an S9 noise level. Reconnect the ground
connection to the tuner the noise drops to less than S2. [BTW: I found
that out quite by accident when I rearranged my station.]

Station grounds can beneficial for several reasons.

Danny, K6MHE

On Jul 30, 2:55 pm, Danny Richardson wrote:


May things you say are correct, but remember that a balun/choke does
not totally choke off (eliminate) common mode current on the
transmission line (particularly a multi-band antenna system) and a
good station ground can provide additional reduction RFI problems.

But again, it's really an antenna/feedline problem, rather than lack
of ground. I'll agree.. Sometimes a ground can "bandaid" certain
problems, but I consider it a last resort solution.


For example here at my station where I have a half way decent single
point RF grounding system. If I remove just my ground connection to my
tuner - leaving everything else intact - and turn on my old CRT
computer monitor I have over an S9 noise level. Reconnect the ground
connection to the tuner the noise drops to less than S2. [BTW: I found
that out quite by accident when I rearranged my station.]

Sounds like that particular antenna system is not very well decoupled
if you are having noise ingress problems of that level.
I have a 21 inch CRT sitting right next to my ungrounded radio and
have no noise problems at all.

Station grounds can beneficial for several reasons.

Well.. Dunno.. I guess for some people.. Myself, I have no need
for one at all. Even running full legal limit power.
I can say for sure, there ain't no way he is going to get a decent
"RF"
ground on the 2nd floor of that building by running a wire to it.
So if I were him, I would forget all about it, and use better, more
modern 21st century techniques to deal with any common mode
problems that might or might not pop up.
MK

On Mon, 30 Jul 2007 13:10:36 -0700, wrote:

Sounds like that particular antenna system is not very well decoupled
if you are having noise ingress problems of that level.
I have a 21 inch CRT sitting right next to my ungrounded radio and
have no noise problems at all.

Not all common mode problems can be fixed by transmission line/antenna
decoupling. Noise can be coupled to the transmission line or other
station equipment (as in my example). It would have made no difference
had I the world's best decoupling choke installed at the transmission
line to antenna transition point the noise would still be there.

Secondly I have never been able to find any broadband balun or choke
(80-10 meters) that is effective on all bands. Indeed, I have measured
the common mode impedance of some commercially made broadband baluns
that have had as little as 100 ohms on some bands while very high on
others. Common mode current will always be with you the only questions
are what is the source and how much. It may be very little and no
consequence while on other bands - particularly in a multi-band
antenna system - it can be substantial.

I have no doubt that your CRT monitor didn't give you any problems
but, then again you weren't using mine. So you are not comparing
apples to apples.

Additionally, you can also have common mode problems via electrical
wiring system. And no matter what you do to decouple the antenna will
have any effect on that but, utilizing a good ground could reduce it
substantially, although, additional filter may be required.

It boils down that a good single point station RF ground system can't
hurt - it can only help. It just an additional protective measure. One
I would not be without.

Danny, K6MHE

On Mon, 30 Jul 2007 19:46:26 +0000 (UTC), John Passaneau
wrote:

Hi:
Interesting web site, but what I meant to say and didn’t do well, is
that if the antenna is installed properly and feed properly with coax
and a balun or open wire line that is properly balanced, there will
never be RF problems that an RF ground in the shack will solve. I had a
problem with 80 meters at high power turning on my furnace. It was
caused by the thermostat line being near resonate at 80 meters. All the
RF grounds in the world would not have helped that, a clamp on ferrite
choke did. It is very hard to get a RF ground in a second floor room.
The idea that one or more ground rods or ground rods and radials outside
with a length of wire running up to a second floor shack will be
anything close to an RF ground at any Ham frequency is just plan wrong.
How ever a lighting ground is a necessity and ground rods work quite
well for that.

John Passaneau W3JXP

Agreed except the only properly built and installed antennas exist in
text books and free space. For the antenna itself (forgetting for the
moment the transmission line) it would have to be installed in a
completely balance environment. Yard clutter such as buildings, trees,
powerlines and etc. would have identical geometry in relation of your
balanced antenna - something that does exist in the real world. Plus
ground conditions under and near the antenna will vary. So there will
be some unbalance. Next add the transmission line. Have you ever seen
a ham station whose transmission line ran perfectly perpendicular from
the antenna to the transmitter? In other words, there will be some
unbalance the only question is how much,

73,
Danny, K6MHE

Agreed except the only properly built and installed antennas exist in
text books and free space. For the antenna itself (forgetting for the
moment the transmission line) it would have to be installed in a
completely balance environment. Yard clutter such as buildings, trees,
powerlines and etc. would have identical geometry in relation of your
balanced antenna - something that does exist in the real world. Plus
ground conditions under and near the antenna will vary. So there will
be some unbalance. Next add the transmission line. Have you ever seen
a ham station whose transmission line ran perfectly perpendicular from
the antenna to the transmitter? In other words, there will be some
unbalance the only question is how much,

73,
Danny, K6MHE






Hi Danny:

You are of course correct, but with RF in the shack problems levels are
important. If the level of RF is below some threshold it causes no harm.
Almost all Ham stations operate just fine with low levels of unbalance
and other defects in the antennas.
Just for interest sake I ran some numbers on a model ground system. Let’s
assume you have a perfect ground system and you connect to it from the
shack on the second floor using 12' of #6 wire. And it runs in a straight
line, no bends or curls. The self inductance of that wire is about
56.22uHy.
So what will be the reactance of that wire at 3.5 MHz? Doing the math I
get 1,235.7ohms. At the other extreme 28MHz, I get 9,886.52ohms. These
are numbers that hardly make me confident that I have any kind of a RF
ground.
By the way at 60Hz the reactance is 0.021ohms that I think is a good
ground.
Please excuse me for harping on this, but I run the electronics shop in
the Physics dept at Penn State University. I'm constantly seeing many
meter long thin wires tied to some cold water pipe or something in a lab
that is supposed to get rid of all the high frequency noise in some
experiment and it has no chance of helping. If physics grad students have
problems understanding grounding it's no wonder that Ham’s do too.

John Passaneau W3JXP

On Mon, 30 Jul 2007 18:47:13 -0500, JOHN PASSANEAU
wrote:


Hi Danny:

You are of course correct, but with RF in the shack problems levels are
important. If the level of RF is below some threshold it causes no harm.
Almost all Ham stations operate just fine with low levels of unbalance
and other defects in the antennas.
Just for interest sake I ran some numbers on a model ground system. Let’s
assume you have a perfect ground system and you connect to it from the
shack on the second floor using 12' of #6 wire. And it runs in a straight
line, no bends or curls. The self inductance of that wire is about
56.22uHy.
So what will be the reactance of that wire at 3.5 MHz? Doing the math I
get 1,235.7ohms. At the other extreme 28MHz, I get 9,886.52ohms. These
are numbers that hardly make me confident that I have any kind of a RF
ground.
By the way at 60Hz the reactance is 0.021ohms that I think is a good
ground.
Please excuse me for harping on this, but I run the electronics shop in
the Physics dept at Penn State University. I'm constantly seeing many
meter long thin wires tied to some cold water pipe or something in a lab
that is supposed to get rid of all the high frequency noise in some
experiment and it has no chance of helping. If physics grad students have
problems understanding grounding it's no wonder that Ham’s do too.

John Passaneau W3JXP

John,

You are absolutely correct. My error was I didn't address the second
story issue. At that location all bets are off and your statements
above are correct. Although using copper strapping with multiple runs
of different lengths from the station to the ground system should
work better.

My station here is on ground level. The distance from the connection
point of the outside ground system to the point inside were all
equipment is connected is about three feet of 3/8" diameter copper
tubing. My frequencies of interest is 80-10 meters. The ground system
consists of eighteen #8 copper radial wires connected to a eight foot
ground rod which serves as the anchor point. The radials are fanned
out over about 210º arc varying in length from as short as about
twenty feet up to seventy feet. It seems to work fairly well.

Thanks for the input and addressing the original poster's question. I
had taken off on a tangent based on the statement that a so called
balanced antenna wouldn't benefit from using a station ground.

Very 73,
Danny, K6MHE

Danny Richardson wrote:
On Mon, 30 Jul 2007 13:10:36 -0700, wrote:


Sounds like that particular antenna system is not very well decoupled
if you are having noise ingress problems of that level.
I have a 21 inch CRT sitting right next to my ungrounded radio and
have no noise problems at all.


Not all common mode problems can be fixed by transmission line/antenna
decoupling. Noise can be coupled to the transmission line or other
station equipment (as in my example). It would have made no difference
had I the world's best decoupling choke installed at the transmission
line to antenna transition point the noise would still be there.

Secondly I have never been able to find any broadband balun or choke
(80-10 meters) that is effective on all bands. Indeed, I have measured
the common mode impedance of some commercially made broadband baluns
that have had as little as 100 ohms on some bands while very high on
others. Common mode current will always be with you the only questions
are what is the source and how much. It may be very little and no
consequence while on other bands - particularly in a multi-band
antenna system - it can be substantial.

I have no doubt that your CRT monitor didn't give you any problems
but, then again you weren't using mine. So you are not comparing
apples to apples.

Additionally, you can also have common mode problems via electrical
wiring system. And no matter what you do to decouple the antenna will
have any effect on that but, utilizing a good ground could reduce it
substantially, although, additional filter may be required.

It boils down that a good single point station RF ground system can't
hurt - it can only help. It just an additional protective measure. One
I would not be without.

Danny, K6MHE




See http://www.audiosystemsgroup.com/RFI-Ham.pdf from Jim Brown. K9YC

An excellent discussion of RFI, interference, chokes, baluns, grounding
with test data and recommendations.

All

I now want to piggyback onto the earlier discussion as i face an even
more difficult siting / grounding issue. I have just installed a 1/2
wave G5RV dipole at approx. 30 ft above ground. My shack is in the
back of the house but on the second floor (effectively in the roof of
the house) above the garden but due to the house design i think i
would struggle to have a RF ground wire of less than 30-40 feet.

Based on above discussions should I :

1) fit a ground rod and run this up to the shack even though its a
long way up along various walls

2) buy an articial ground unit such as the MFJ-931

3) forget about it and make do without a ground.

I am pretty thoroughly confused.

Thanks

Andy

On Thu, 02 Aug 2007 12:55:05 -0700, wrote:

All

I now want to piggyback onto the earlier discussion as i face an even
more difficult siting / grounding issue. I have just installed a 1/2
wave G5RV dipole at approx. 30 ft above ground. My shack is in the
back of the house but on the second floor (effectively in the roof of
the house) above the garden but due to the house design i think i
would struggle to have a RF ground wire of less than 30-40 feet.

Based on above discussions should I :

1) fit a ground rod and run this up to the shack even though its a
long way up along various walls

2) buy an articial ground unit such as the MFJ-931

3) forget about it and make do without a ground.

I am pretty thoroughly confused.

Thanks

Andy

The G5RV dipole is a balanced antenna and does not require a ground.
So unless you want one for some other reason, option 3...

bob
k5qwg