Station With Center-Fed Dipole - Best Grounding Technique?
 

dave wrote:
Jim Lux wrote:

Certainly, a choke at the entrance to the shack is a great way to keep
RF outside.

A choke wastes power.

A properly designed common mode choke does not waste power.

Roy Lewallen, W7EL

Station With Center-Fed Dipole - Best Grounding Technique?
 

dave wrote:
Jim Lux wrote:
Howard Lester wrote:
"dave" wrote

A BalUn would help a lot.

For what? If the antenna system is balanced (as are dipoles,
inherently), I seriously doubt a balun would be good for anything.


Most every practical dipole installation has some imbalance in the
installation (the trees are closer to one side than the other, etc.)..
a choke to prevent RF current from flowing on the outside of the
feedline will at least make the pattern more consistent with
expectations. Might make the tuning less "twitchy" too (because you've
decoupled the effect of things near the feedline).

Certainly, a choke at the entrance to the shack is a great way to keep
RF outside.

A choke wastes power.

How might this happen? The choke's not in the desired RF path (i.e. the
inside of the coax and the antenna itself)

Putting an RF impedance of, say, 5K in series with the current on the
OUTSIDE of the shield should effectively reduce the current to zero, so
there's no power being dissipated in the choke.

Yes, if you use a choke with too low an impedance, it might dissipate power.

Station With Center-Fed Dipole - Best Grounding Technique?
 

Tom Ring wrote:

He's feeding it with coax, so it's not just a good idea, it's
required.

The antenna is balanced, the feedline is not. He stated the
feedline is RG-8X.


The assembly instructions for the antenna say...

The antenna is "..designed to be used with
50 ohm coax cable. No balun is required for
proper operation.

If RF on the coax is a problem, simply wind
a "choke balun" with the coax that's used for
your feedline. Wind approx 8 turns, at about
an 8 inch diameter and tape (with outdoor rated
black electrical tape), like a donut, and place
this "donut" near the feedpoint of the antenna.
You should leave about 2 foot of your coax
sticking out of this "donut" for connection to
the antenna. Then attach the end of your
coax to the antenna connector on the center
insulator, with the coax connector that is
already on your feed line."

In other words, a scramble-winding choke near the antenna's feedpoint,
which I'll add if RF becomes an issue. As stated in my first message
("don't believe RF is an issue with a dipole," which should probably
read "major issue"), I'm much more concerned with safety and lightning
protection.

stewart / w5net

Station With Center-Fed Dipole - Best Grounding Technique?
 

Jim Lux wrote:

Or, easier.. put a choke around the feedline where it comes
into the shack, so that there's no appreciable RF current
through the chassis and green-wire ground.


Okay, I'm adding a balun. Now the question is what and where. The
assembly instructions for the antenna say...

The antenna is "..designed to be used with
50 ohm coax cable. No balun is required for
proper operation.

If RF on the coax is a problem, simply wind
a "choke balun" with the coax that's used for
your feedline. Wind approx 8 turns, at about
an 8 inch diameter and tape (with outdoor rated
black electrical tape), like a donut, and place
this "donut" near the feedpoint of the antenna.
You should leave about 2 foot of your coax
sticking out of this "donut" for connection to
the antenna. Then attach the end of your
coax to the antenna connector on the center
insulator, with the coax connector that is
already on your feed line."

In other words, a scramble-winding choke near the antenna's feedpoint.
The alternative is an MFJ-915 in-line balun with 50 ferrite core beads
on coax (cheaper than I can buy the ferrites), which MFJ says should
be installed closer to the radio (3 feet) as opposed to the antenna
feedpoint at the other end of the coax as described above.

Which of the two options is most sufficient for the task and which is
the correct placement for this - or are they both right depending on
the type?

stewart / w5net

Station With Center-Fed Dipole - Best Grounding Technique?
 

On Wed, 06 May 2009 01:54:34 +0200, noname wrote:

Okay, I'm adding a balun. Now the question is what and where. The
assembly instructions for the antenna say...

Hi Stewart,

The answer to that is driven by the perceived problem. In a nutshell,
if you don't have a problem, you don't need the balun (or choke).

Knowing that you have a problem is another matter; but if you don't
know what the problem is (the perception), you wouldn't know if it got
fixed either.

73's
Richard Clark, KB7QHC

Station With Center-Fed Dipole - Best Grounding Technique?
 

noname wrote:
Jim Lux wrote:
Or, easier.. put a choke around the feedline where it comes
into the shack, so that there's no appreciable RF current
through the chassis and green-wire ground.


Okay, I'm adding a balun. Now the question is what and where. The
assembly instructions for the antenna say...

The antenna is "..designed to be used with
50 ohm coax cable. No balun is required for
proper operation.

If RF on the coax is a problem, simply wind
a "choke balun" with the coax that's used for
your feedline. Wind approx 8 turns, at about
an 8 inch diameter and tape (with outdoor rated
black electrical tape), like a donut, and place
this "donut" near the feedpoint of the antenna.
You should leave about 2 foot of your coax
sticking out of this "donut" for connection to
the antenna. Then attach the end of your
coax to the antenna connector on the center
insulator, with the coax connector that is
already on your feed line."

In other words, a scramble-winding choke near the antenna's feedpoint.
The alternative is an MFJ-915 in-line balun with 50 ferrite core beads
on coax (cheaper than I can buy the ferrites), which MFJ says should
be installed closer to the radio (3 feet) as opposed to the antenna
feedpoint at the other end of the coax as described above.

Which of the two options is most sufficient for the task and which is
the correct placement for this - or are they both right depending on
the type?



Read Jim Brown's RFI-Ham.pdf referenced in an earlier post.

"choke baluns" made by winding coax are pretty much single band devices.

A better approach is a single 2.4" toroid of suitable mix (#31 is good),
and put a dozen turns of your RG-8x on it. Put one at the feedpoint,
put one where it comes in the shack. Buy some extra cores because they
make good RF filters for things like power cords (and the hole is big
enough that a standard IEC power connector will fit through them)

The MFJ915 is fine, although I wasn't able to find any actual
performance specifications or details of what mix they're using. (in a
few minutes of casual googling).. MFJs is probably an incarnation of the
"W2DU balun", so the data Jim measured is probably reasonable. (about
1500ohms peaking at 10MHz)

I think you'll get better results (cheaper) with the single big
toroid..5 turns gives you more impedance than the W2DU, and it goes up
from there ( based on the measurements in K9YCs paper.. page 12). The
toroids run about $5. Most of the gain is from using a better mix (31)

Station With Center-Fed Dipole - Best Grounding Technique?
 

Richard Clark wrote:

Hi Steve,


I assume you're talking to me since you replied to my message. My name
is Stewart, not Steve.


So, in fact your three prong plugs find their way to the
panel ground. Can YOU find that ground?


I don't understand your question. The radio chassis is grounded to the
wall outlet. The overall house wiring was recently inspected, with the
grounding checked at that time. It was a thorough inspection which
also included a device plugged into most outlets to check the wiring.
Given that, I don't really know what I'm supposed to find and why.


So, by this explicit statement, your "balanced" antenna
has been unbalanced at the rig (which only further enforces
the unbalance by virtue of the coax connection).


I guess so. Actually, I don't really know. The radio was manufactured
with the chassis grounded to the wall outlet and the antenna was
designed by it's manufacturer to work properly with 50 ohm coax feed
connected (I would assume) to a radio like this. What impact that has
on balanced versus unbalanced is beyond me, and the same is true for
what exactly you want me to do about it.

stewart / w5net

Station With Center-Fed Dipole - Best Grounding Technique?
 

Richard Clark wrote:

Hi Stewart,

The answer to that is driven by the perceived problem. In a
nutshell, if you don't have a problem, you don't need the
balun (or choke).

Knowing that you have a problem is another matter; but if
you don't know what the problem is (the perception), you
wouldn't know if it got fixed either.


Wow, your messages get more cryptic as they go along. I thought the
very first message made it clear I'm not trying to fix a specific
problem, but instead trying to head off some of the more common
problems associated with a setup like this.

Again, this is an entirely a new setup which has not been installed
yet. What I'm seeking here is some input on the best way to do that.
I'm fairly familiar with the basics of dipole antennas, but hoping for
some solid advice from those with a lot more experience than my own.

stewart / w5net

Station With Center-Fed Dipole - Best Grounding Technique?
 

On May 5, 7:26*pm, Jim Lux wrote:
noname wrote:
Jim Lux wrote:
Or, easier.. put a choke around the feedline where it comes
into the shack, so that there's no appreciable RF current
through the chassis and green-wire ground.

Okay, I'm adding a balun. Now the question is what and where. The
assembly instructions for the antenna say...

* The antenna is "..designed to be used with
* 50 ohm coax cable. No balun is required for
* proper operation.

* If RF on the coax is a problem, simply wind
* a "choke balun" with the coax that's used for
* your feedline. Wind approx 8 turns, at about
* an 8 inch diameter and tape (with outdoor rated
* black electrical tape), like a donut, and place
* this "donut" near the feedpoint of the antenna.
* You should leave about 2 foot of your coax
* sticking out of this "donut" for connection to
* the antenna. Then attach the end of your
* coax to the antenna connector on the center
* insulator, with the coax connector that is
* already on your feed line."

In other words, a scramble-winding choke near the antenna's feedpoint.
The alternative is an MFJ-915 in-line balun with 50 ferrite core beads
on coax (cheaper than I can buy the ferrites), which MFJ says should
be installed closer to the radio (3 feet) as opposed to the antenna
feedpoint at the other end of the coax as described above.

Which of the two options is most sufficient for the task and which is
the correct placement for this - or are they both right depending on
the type?

Read Jim Brown's RFI-Ham.pdf referenced in an earlier post.

"choke baluns" made by winding coax are pretty much single band devices.

A better approach is a single 2.4" toroid of suitable mix (#31 is good),
and put a dozen turns of your RG-8x on it. * Put one at the feedpoint,
put one where it comes in the shack. *Buy some extra cores because they
make good RF filters for things like power cords (and the hole is big
enough that a standard IEC power connector will fit through them)

The MFJ915 is fine, although I wasn't able to find any actual
performance specifications or details of what mix they're using. (in a
few minutes of casual googling).. MFJs is probably an incarnation of the
"W2DU balun", so the data Jim measured is probably reasonable. (about
1500ohms peaking at 10MHz)

I think you'll get better results (cheaper) with the single big
toroid..5 turns gives you more impedance than the W2DU, and it goes up
from there ( based on the measurements in K9YCs paper.. page 12). The
toroids run about $5. *Most of the gain is from using a better mix (31)

What if you use a coax with two shields, one shield for chassis ground
which is the coax connection and the outer shield for earth/ground?
Yes, there could be a ground loop but the nearest ground to a strike/
antenna is probably the best protection

Station With Center-Fed Dipole - Best Grounding Technique?
 

On Wed, 06 May 2009 02:55:54 +0200, noname wrote:

Richard Clark wrote:

Hi Stewart,

The answer to that is driven by the perceived problem.
I'm not trying to fix a specific problem

Then there's no reason to fix imagined ones.

Again, this is an entirely a new setup which has not been installed
yet.

Grounding has been covered, but, likely as not, you will have more
problems there than anything over the air.

As for antennas, I've read the advice offered to you by MFJ. Belts
and suspenders kind of stuff, but that is the level of advice you can
expect until you discover something wrong. Do everything suggested,
and then do it again at different places. [Cryptic as it seems,
eventually this lesson will emerge from the reams of advice.]

You ask to prevent problems and I have pointed out they are only
problems if you think (or get burnt when) they are. A bajillion
operators live lives of happy operation with none of those "solutions"
in place. Fix their "problems" and likely as not, nothing will get
noticeably better, could eliminate some former contacts, and only make
them grumpy about engineers crimping their fun.

73's
Richard Clark, KB7QHC