On Wed, 03 Nov 2004 01:59:15 -0800, "Guntier C."
wrote:

I received and old wilson 1000 mag. mount and want to put it on my quad
(4 magnet) mount. I hear that I need a 18 ft. piece of coax for a
counterpoise. Is that true? Any info appreciated.

Thanks,

G.C.


I'll get slammed for posting the correct answer but what else is new.

Manufacturers of Magnetic mount antennas recommend keeping the
original length of coax.( Wilson, K40, RS, Antenna Specialist, ect.).
Why do they do that? The answer is simple. They realize that there
is no such thing as a perfect or exact scenario for an antenna
installation. They know that in a typical installation of their
antenna the coax length will most likely come into play and can
be beneficial. It can be beneficial in that typically the radio will
see a better load with the manufacturers recommended coax length.

It's not that these antennas can't work with any length of coax. It's
just that in most cases you'll get better results with the recommended
length.

wrote in message
...
On Wed, 03 Nov 2004 01:59:15 -0800, "Guntier C."
wrote:

I received and old wilson 1000 mag. mount and want to put it on my quad
(4 magnet) mount. I hear that I need a 18 ft. piece of coax for a
counterpoise. Is that true? Any info appreciated.

Thanks,

G.C.


I'll get slammed for posting the correct answer but what else is new.

Manufacturers of Magnetic mount antennas recommend keeping the
original length of coax.( Wilson, K40, RS, Antenna Specialist, ect.).
Why do they do that? The answer is simple. They realize that there
is no such thing as a perfect or exact scenario for an antenna
installation. They know that in a typical installation of their
antenna the coax length will most likely come into play and can
be beneficial. It can be beneficial in that typically the radio will
see a better load with the manufacturers recommended coax length.

It's not that these antennas can't work with any length of coax. It's
just that in most cases you'll get better results with the recommended
length.

Agreed with tnon. As soon as someone mentions about using a certain length
of coax with the CB antenna someone always asssumes it is to adjust SWR. It
will not do this. It will change the impedance the radio sees which is not
the same as changing the SWR. For example if the impedance of the antenna is
25 ohms 18ft of coax will make the antenna appear as 100 ohms at the radio.
SWR will be 2:1 reguardless of the length of the cable. AS most radios are
antennas are installed plug and go without benifit of tuning and most all CB
antenas represent an impedance lower than 50 ohms antenna manufactures
typically reccomend the 18ft coax for best results under these conditions.
Most radios work better if they are mismatched above 50 than below 50. This
really becomes noticable if SWR is around 3:1. Not uncommon on a typical
plug and go installation. Otherwise length does not matter much on a well
tuned and properly installed radio and antenna.

Jimmie:

SWR is a direct measurement of impedance mismatch. If you change the
coax length, thereby changing the angle the coax is conducting, and
the SWR changes, then there is something wrong with the antenna itself
that needs to be fixed.

Physics dictates this. There's no way around it.

Coax Length DOES NOT MATTER for a single antenna setup. Period.

-SSB

Jimmie wrote:

wrote in message
...

On Wed, 03 Nov 2004 01:59:15 -0800, "Guntier C."
wrote:


I received and old wilson 1000 mag. mount and want to put it on my quad
(4 magnet) mount. I hear that I need a 18 ft. piece of coax for a
counterpoise. Is that true? Any info appreciated.

Thanks,

G.C.


I'll get slammed for posting the correct answer but what else is new.

Manufacturers of Magnetic mount antennas recommend keeping the
original length of coax.( Wilson, K40, RS, Antenna Specialist, ect.).
Why do they do that? The answer is simple. They realize that there
is no such thing as a perfect or exact scenario for an antenna
installation. They know that in a typical installation of their
antenna the coax length will most likely come into play and can
be beneficial. It can be beneficial in that typically the radio will
see a better load with the manufacturers recommended coax length.

It's not that these antennas can't work with any length of coax. It's
just that in most cases you'll get better results with the recommended
length.


Agreed with tnon. As soon as someone mentions about using a certain length
of coax with the CB antenna someone always asssumes it is to adjust SWR. It
will not do this. It will change the impedance the radio sees which is not
the same as changing the SWR. For example if the impedance of the antenna is
25 ohms 18ft of coax will make the antenna appear as 100 ohms at the radio.
SWR will be 2:1 reguardless of the length of the cable. AS most radios are
antennas are installed plug and go without benifit of tuning and most all CB
antenas represent an impedance lower than 50 ohms antenna manufactures
typically reccomend the 18ft coax for best results under these conditions.
Most radios work better if they are mismatched above 50 than below 50. This
really becomes noticable if SWR is around 3:1. Not uncommon on a typical
plug and go installation. Otherwise length does not matter much on a well
tuned and properly installed radio and antenna.

On Thu, 04 Nov 2004 19:33:08 GMT, sideband wrote:

Jimmie:

SWR is a direct measurement of impedance mismatch. If you change the
coax length, thereby changing the angle the coax is conducting, and
the SWR changes, then there is something wrong with the antenna itself
that needs to be fixed.

Physics dictates this. There's no way around it.

Coax Length DOES NOT MATTER for a single antenna setup. Period.

-SSB

I'd only agree if the antenna perfectly decoupled and was a perfect
load for the radio. In other words if everything operated perfectly
in a perfect world.

As far as mag mounts and using a automobiles as a counterpoise ? ? ?
That scenario is not even close to a perfect world.

I often wonder why there is so much criticism when one suggests
using the manufacturers recommended length. This criticism seems to
be followed by the statement that "any length will do". They believe
that 10 feet, 11 feet, 13.5 feet,ect. ect. are fine. Just don't pick
18 feet !!!!!! How hypocritical is that? Isn't 18' also a length
contained within the statement "any length will do"?

tnom:

Explain this, then... CB radio in my Peterbilt, with a mirror mounted
Hustler HQ-27 on the driver's side.. 6 feet of coax shows a 1:1 on 19,
1.1:1 on 1, and 1.1:1 on 40... 12 feet of coax shows the same
readings... 18 feet of coax shows.. guess what? the SAME RESULTS.

IT IS possible to get near "perfect world" results with a little work,
and attention to detail.

By the way, I've gotten similar results on two meters with a magnet
mount 5/8 2M Lakeview whip on my old Ford LTLA9000. Had to shorten the
coax because I was sick of the bundle of it in the cab... no change in
SWR over a four MHz bandwidth...

There goes the "magmount theory" as well..

If changing the length of the coax changes the SWR, then there is
something wrong with the antenna.

-SSB

wrote:

I'd only agree if the antenna perfectly decoupled and was a perfect
load for the radio. In other words if everything operated perfectly
in a perfect world.

As far as mag mounts and using a automobiles as a counterpoise ? ? ?
That scenario is not even close to a perfect world.

I often wonder why there is so much criticism when one suggests
using the manufacturers recommended length. This criticism seems to
be followed by the statement that "any length will do". They believe
that 10 feet, 11 feet, 13.5 feet,ect. ect. are fine. Just don't pick
18 feet !!!!!! How hypocritical is that? Isn't 18' also a length
contained within the statement "any length will do"?

On Thu, 04 Nov 2004 21:59:02 GMT, sideband wrote:

tnom:

Explain this, then... CB radio in my Peterbilt, with a mirror mounted
Hustler HQ-27 on the driver's side.. 6 feet of coax shows a 1:1 on 19,
1.1:1 on 1, and 1.1:1 on 40... 12 feet of coax shows the same
readings... 18 feet of coax shows.. guess what? the SAME RESULTS.

IT IS possible to get near "perfect world" results with a little work,
and attention to detail.

By the way, I've gotten similar results on two meters with a magnet
mount 5/8 2M Lakeview whip on my old Ford LTLA9000. Had to shorten the
coax because I was sick of the bundle of it in the cab... no change in
SWR over a four MHz bandwidth...

There goes the "magmount theory" as well..

If changing the length of the coax changes the SWR, then there is
something wrong with the antenna.

-SSB

SSB;
I know this was addressed to Tnom, hope you don't mind my 2-cents
worth.

Very few mag mounts have an adequate "RF" ground, at least on 11
meters or lower. There isn't enough capacitive coupling to the
vehicle body. In some cases the length of the coax can matter, not
from a matching point of view, but as a counterpoise for the antenna.
I have seen mag mount installations where you could see the SWR change
just by moving the coax around.

"Lancer" wrote in message
ews.com...
On Thu, 04 Nov 2004 21:59:02 GMT, sideband wrote:

tnom:

Explain this, then... CB radio in my Peterbilt, with a mirror mounted
Hustler HQ-27 on the driver's side.. 6 feet of coax shows a 1:1 on 19,
1.1:1 on 1, and 1.1:1 on 40... 12 feet of coax shows the same
readings... 18 feet of coax shows.. guess what? the SAME RESULTS.

IT IS possible to get near "perfect world" results with a little work,
and attention to detail.

By the way, I've gotten similar results on two meters with a magnet
mount 5/8 2M Lakeview whip on my old Ford LTLA9000. Had to shorten the
coax because I was sick of the bundle of it in the cab... no change in
SWR over a four MHz bandwidth...

There goes the "magmount theory" as well..

If changing the length of the coax changes the SWR, then there is
something wrong with the antenna.

-SSB

SSB;
I know this was addressed to Tnom, hope you don't mind my 2-cents
worth.

Very few mag mounts have an adequate "RF" ground, at least on 11
meters or lower. There isn't enough capacitive coupling to the
vehicle body. In some cases the length of the coax can matter, not
from a matching point of view, but as a counterpoise for the antenna.
I have seen mag mount installations where you could see the SWR change
just by moving the coax around.

Please explain how a poor "RF ground" can be corrected by increasing coax
length??

Don

Dunno about you, Lancer, but the last thing I'd want is RF inside the
vehicle.. which is exactly what's happening if you're using the coax
braid as the counterpoise/image plane/groundplane...even partially.

-SSB

Lancer wrote:


SSB;
I know this was addressed to Tnom, hope you don't mind my 2-cents
worth.

Very few mag mounts have an adequate "RF" ground, at least on 11
meters or lower. There isn't enough capacitive coupling to the
vehicle body. In some cases the length of the coax can matter, not
from a matching point of view, but as a counterpoise for the antenna.
I have seen mag mount installations where you could see the SWR change
just by moving the coax around.

"Lancer" wrote in message
ews.com...
On Thu, 04 Nov 2004 21:59:02 GMT, sideband wrote:

tnom:

Explain this, then... CB radio in my Peterbilt, with a mirror mounted
Hustler HQ-27 on the driver's side.. 6 feet of coax shows a 1:1 on 19,
1.1:1 on 1, and 1.1:1 on 40... 12 feet of coax shows the same
readings... 18 feet of coax shows.. guess what? the SAME RESULTS.

IT IS possible to get near "perfect world" results with a little work,
and attention to detail.

By the way, I've gotten similar results on two meters with a magnet
mount 5/8 2M Lakeview whip on my old Ford LTLA9000. Had to shorten the
coax because I was sick of the bundle of it in the cab... no change in
SWR over a four MHz bandwidth...

There goes the "magmount theory" as well..

If changing the length of the coax changes the SWR, then there is
something wrong with the antenna.

-SSB

SSB;
I know this was addressed to Tnom, hope you don't mind my 2-cents
worth.

Very few mag mounts have an adequate "RF" ground, at least on 11
meters or lower. There isn't enough capacitive coupling to the
vehicle body. In some cases the length of the coax can matter, not
from a matching point of view, but as a counterpoise for the antenna.
I have seen mag mount installations where you could see the SWR change
just by moving the coax around.

This is true but is totally beside the point of why manufacturers reccomend
18ft of coax. If you have the problem you mentioned fix the ground dont play
with the coax length. A good test for a CB antenna is to temporarily splice
in 6 ft of coax . If your SWR changes your ground is probably bad.Poorly
made SWR meters will cause this too.

On Thu, 04 Nov 2004 21:59:02 GMT, sideband wrote
in :

tnom:

Explain this, then... CB radio in my Peterbilt, with a mirror mounted
Hustler HQ-27 on the driver's side..


Nice antenna! Installed one recently and plan on getting one for
myself.


6 feet of coax shows a 1:1 on 19,
1.1:1 on 1, and 1.1:1 on 40... 12 feet of coax shows the same
readings... 18 feet of coax shows.. guess what? the SAME RESULTS.


Your antenna mount has a good RF ground. Coax length is going to make
little if any difference.


IT IS possible to get near "perfect world" results with a little work,
and attention to detail.

By the way, I've gotten similar results on two meters with a magnet
mount 5/8 2M Lakeview whip on my old Ford LTLA9000. Had to shorten the
coax because I was sick of the bundle of it in the cab... no change in
SWR over a four MHz bandwidth...


Now -that- I find hard to believe. If you get relatively flat
bandwidth over 4MHz then your antenna is basically nothing more than a
dummy load, and coax length doesn't matter there either.


There goes the "magmount theory" as well..


You didn't read the results of my tests a few months ago, did you?


If changing the length of the coax changes the SWR, then there is
something wrong with the antenna.


Absolutely correct, and the problem is an inadequate RF ground at the
mount, which is typical of mag-mounts (unless they are so heavily
loaded with resistance that they act like dummy loads).






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