wrote:

Again, with a properly installed single antenna, coax length does not
matter.

-SSB

This thread was about a ......................

1. mag mount
2. on a vehilcle
3. with a recommended coax length

Does this thread represent a "properly installed single antenna"?

It usually represents a disagreement no matter how it's worded.

--
http://NewsReader.Com
30GB/Month

On 05 Nov 2004 13:08:42 GMT, Steveo
wrote:

wrote:

Again, with a properly installed single antenna, coax length does not
matter.

-SSB

This thread was about a ......................

1. mag mount
2. on a vehilcle
3. with a recommended coax length

Does this thread represent a "properly installed single antenna"?

It usually represents a disagreement no matter how it's worded.

Yes. Coax length creates static. It's an electrical fact.

Hello All:

I have been reading most of the thread here and its quit good reading.

Great inputs from Frank, Sideband, Jimmie Lancer, Tnom, and others.

One main consideration on the magnetic mount antennas is that the coax
is being used as a counter poise and a lead for capacitance to ground.
So I can see where a manufacture will specify a 3/4 wavelength length of
coax, 18 feet.

Anytime you use the coax as a counter poise or other end of the antenna
coax lengths will effect the SWR, as the coax is no longer a simply a
transmission line, but now also a antenna. I would love to have the time
to do more testing.

You will not see this type of design in Military, Commercial, or Amateur
Antennas.

I got a old Wilson 5000 magnetmatic mount antenna that I rebuilt and use
on my car. I replaced the Krapy RG58C coax with "18" Ft of RG142B Teflon
type coax that is bullet proof. It works great. I get it surplus at times.

But I wanted to add 3 or 4 each, 9 foot ground plane radial wires, being
run over the body of the car, from the base of the antenna, connected to
the shield of the coax. And do a few tests. Food for thought.

One thing I may do as a quick add on improvement is add in a Toroid Core
in the coax about 9 feet down the coax from the antenna. Wrapping the
coax around a 2.4 inch OD Amidon Toroid Core, will choke the outer coax
shield currents from going farther down the coax, but allowing a 1/4
wave of coax to be a counter poise. Worth a try I think. It will also
reduce some interference noise heard by the radio, that are coming in
from the ungrounded shield of the coax. Neat-Oh!

Suggested Toroid Core Amidon FT-240-61
Amidon is at: http://www.amidoncorp.com/aai_productselection.htm

Jay in the Mojave

Kreedentials:
Rock n Roll Fan
Owner 1967 Ford F250, 4x4, with worlds loudest PA System
Took Electronics in 8th grade, way more better than that ackademic crap
that schools now teach kids now a days ancient European history, liberal
arts, and in incoming paper clips, in place of industrial arts.
Paid Member of Mojave Desert Radio Club, 9 dollars now.
Radio enthusiast type of guy

On Fri, 05 Nov 2004 08:13:49 -0800, Jay in the Mojave
wrote in :

Hello All:

I have been reading most of the thread here and its quit good reading.

Great inputs from Frank, Sideband, Jimmie Lancer, Tnom, and others.

One main consideration on the magnetic mount antennas is that the coax
is being used as a counter poise and a lead for capacitance to ground.
So I can see where a manufacture will specify a 3/4 wavelength length of
coax, 18 feet.


The purpose of using 18 feet is not to effect a counterpoise but to
mirror the RF potential of the shield at both ends of the coax,
assuming that at least one end is properly grounded. IOW, if the radio
has a good RF ground but the antenna mount is poorly grounded (like a
mag-mount), using a 1/2 wave (as measured on the -outside- of the
shield) will prevent the antenna end from floating. Or vice-versa.


Anytime you use the coax as a counter poise or other end of the antenna
coax lengths will effect the SWR, as the coax is no longer a simply a
transmission line, but now also a antenna. I would love to have the time
to do more testing.

You will not see this type of design in Military, Commercial, or Amateur
Antennas.

I got a old Wilson 5000 magnetmatic mount antenna that I rebuilt and use
on my car. I replaced the Krapy RG58C coax with "18" Ft of RG142B Teflon
type coax that is bullet proof. It works great. I get it surplus at times.

But I wanted to add 3 or 4 each, 9 foot ground plane radial wires, being
run over the body of the car, from the base of the antenna, connected to
the shield of the coax. And do a few tests. Food for thought.


Here's something to try: Set your GDO for 27MHz and run it over your
vehicle. Some places will dip more than others indicating better RF
grounds, and therefore better places to drill.


One thing I may do as a quick add on improvement is add in a Toroid Core
in the coax about 9 feet down the coax from the antenna. Wrapping the
coax around a 2.4 inch OD Amidon Toroid Core, will choke the outer coax
shield currents from going farther down the coax, but allowing a 1/4
wave of coax to be a counter poise. Worth a try I think. It will also
reduce some interference noise heard by the radio, that are coming in
from the ungrounded shield of the coax. Neat-Oh!

Suggested Toroid Core Amidon FT-240-61
Amidon is at: http://www.amidoncorp.com/aai_productselection.htm


A sleeve with a high perm (u=850) should also work at 27MHz. As
chokes I've seen them used at the radio end, but maybe using one at
the antenna end will improve the performance of a mag-mount....? I
might just try that myself someday.






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Jay:

Thanks for your input.. A couple of things, though..

If the coax is being used as a counterpoise, it's not part of a
capacitive grounding system.

The capacitive ground comes from the metallic base/magnet mount to the
vehicle body, not from the coax.

-SSB

Jay in the Mojave wrote:

Hello All:

I have been reading most of the thread here and its quit good reading.

Great inputs from Frank, Sideband, Jimmie Lancer, Tnom, and others.

One main consideration on the magnetic mount antennas is that the coax
is being used as a counter poise and a lead for capacitance to ground.
So I can see where a manufacture will specify a 3/4 wavelength length of
coax, 18 feet.

Anytime you use the coax as a counter poise or other end of the antenna
coax lengths will effect the SWR, as the coax is no longer a simply a
transmission line, but now also a antenna. I would love to have the time
to do more testing.

You will not see this type of design in Military, Commercial, or Amateur
Antennas.

I got a old Wilson 5000 magnetmatic mount antenna that I rebuilt and use
on my car. I replaced the Krapy RG58C coax with "18" Ft of RG142B Teflon
type coax that is bullet proof. It works great. I get it surplus at times.

But I wanted to add 3 or 4 each, 9 foot ground plane radial wires, being
run over the body of the car, from the base of the antenna, connected to
the shield of the coax. And do a few tests. Food for thought.

One thing I may do as a quick add on improvement is add in a Toroid Core
in the coax about 9 feet down the coax from the antenna. Wrapping the
coax around a 2.4 inch OD Amidon Toroid Core, will choke the outer coax
shield currents from going farther down the coax, but allowing a 1/4
wave of coax to be a counter poise. Worth a try I think. It will also
reduce some interference noise heard by the radio, that are coming in
from the ungrounded shield of the coax. Neat-Oh!

Suggested Toroid Core Amidon FT-240-61
Amidon is at: http://www.amidoncorp.com/aai_productselection.htm

Jay in the Mojave

Kreedentials:
Rock n Roll Fan
Owner 1967 Ford F250, 4x4, with worlds loudest PA System
Took Electronics in 8th grade, way more better than that ackademic crap
that schools now teach kids now a days ancient European history, liberal
arts, and in incoming paper clips, in place of industrial arts.
Paid Member of Mojave Desert Radio Club, 9 dollars now.
Radio enthusiast type of guy

On Fri, 05 Nov 2004 22:22:03 GMT, sideband wrote
in :

Jay:

Thanks for your input.. A couple of things, though..

If the coax is being used as a counterpoise, it's not part of a
capacitive grounding system.

The capacitive ground comes from the metallic base/magnet mount to the
vehicle body, not from the coax.


That was an issue when I did the mag-mount tests a few months ago. As
it turns out, the coax can provide plenty of capacitive coupling to
the vehicle, even more than the mag-mount under certain conditions.
But neither of them provide much coupling, not nearly as much as would
be needed to compare with a properly mounted base.






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Agreed on the not-enough ground.. that's why counterpoise kits were
available for the W1000's... I had one that worked tits.

-SSB

Frank Gilliland wrote:

On Fri, 05 Nov 2004 22:22:03 GMT, sideband wrote
in :


Jay:

Thanks for your input.. A couple of things, though..

If the coax is being used as a counterpoise, it's not part of a
capacitive grounding system.

The capacitive ground comes from the metallic base/magnet mount to the
vehicle body, not from the coax.



That was an issue when I did the mag-mount tests a few months ago. As
it turns out, the coax can provide plenty of capacitive coupling to
the vehicle, even more than the mag-mount under certain conditions.
But neither of them provide much coupling, not nearly as much as would
be needed to compare with a properly mounted base.






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Hello Sideband:

Really! What counterpoise kits?!?!?!?!?!??!!??!?!?!?
Who sold them, what, when, where?

Jay in the Mojave

Kreedentials:
Rock n Roll Fan
Owner 1967 Ford F250, 4x4, with worlds loudest PA System
Took Electronics in 8th grade, way more better than that ackademic crap
that schools now teach kids now a days, ancient European history,
liberal arts, and in incoming paper clips, in place of industrial arts.
Paid Member of Mojave Desert Radio Club, 9 dollars now. (Big party
coming up soon)
Radio enthusiast type of guy

sideband wrote:
Agreed on the not-enough ground.. that's why counterpoise kits were
available for the W1000's... I had one that worked tits.

-SSB