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

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

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

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

"noname" wrote in message
...



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.


Matching issues aside, common thinking on the balun issue is that it greatly
attenuates current on the outside of the coax.

In certain rare cases, I suppose such current could be a good thing, giving
additional radiation in a desired direction, but I'd never try to predict it
or control it. Use the balun because the benefits of keeping the RF "out
there" are considerable: Less TVI, no false ringing of your telephones, less
squawking from your computer speakers, no computer mouse or keyboard doing
its own thing, no cable modem resetting itself, no RF burns on your
fingertips (although there are other ways to get them, hi-hi).

The lack of a balun may not cause every listed malady, above, but that's a
short list of some that I have caused or witnessed from a quick-rig antenna
that didn't have a balun. They went away when one was installed.

Sal M. Onella wrote:
In certain rare cases, I suppose such current could be a good thing, giving
additional radiation in a desired direction, but I'd never try to predict it
or control it.

The Carolina Windom folk advertise feedline
radiation as an advantage over other antennas
and charge extra $ for it. :-)
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

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)

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

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

You'll still need to deal with RF currents flowing on the outside of the
coax (and also potentially between inner and outer shields).

A good transient suppression scheme at the entry point deals with the
overvoltages from lightning, power lines falling on your antenna, etc.

The challenge is in protecting a sensitive receiver front end, while not
introducing other problems: if the receiver burns out at 1Volt, a clamp
at 300V isn't going to save the front end, although it will keep the
radio from catching on fire. A diode clamp to the supply rails or
similar will save the front end, but will almost certainly result in IMD
issues with strong input signals. Sometimes, the front end just has to
be the sacrificial "fuse", so you want to make sure that it's a cheap &
replaceable part that suffers.

On May 6, 11:36*am, Jim Lux wrote:
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

You'll still need to deal with RF currents flowing on the outside of the
coax (and also potentially between inner and outer shields).

A good transient suppression scheme at the entry point deals with the
overvoltages from lightning, power lines falling on your antenna, etc.

The challenge is in protecting a sensitive receiver front end, while not
introducing other problems: *if the receiver burns out at 1Volt, a clamp
at 300V isn't going to save the front end, although it will keep the
radio from catching on fire. *A diode clamp to the supply rails or
similar will save the front end, but will almost certainly result in IMD
issues with strong input signals. *Sometimes, the front end just has to
be the sacrificial "fuse", so you want to make sure that it's a cheap &
replaceable part that suffers.

Let me try again and put it another way. What if:
The transmission line is a two parallel wire system.This is enclosed
in one sided metalized mylar isolated shielding Total covered with
insulation and wire netting for true ground ? All of the above buried
in ground