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

On Thu, 4 Nov 2004 20:07:21 -0500, "M-Tech"
wrote in :

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


A given length of coax runs from the radio to the antenna mount. If
the shield is not adequately grounded (RF ground) then RF will crawl
onto the outside of the shield. When that happens your coax behaves
like an antenna, having resonant and non-resonant lengths. When that
happens, different lengths of the coax will put the antenna mount at
different phase angles, therefore changing the load impedance and SWR.
There are only two solutions: Provide a good RF ground to the antenna
mount (preferred), or change the length of the coax to 'tune' the
input impedance of the antenna.

That's all assuming your radio is fixed to a good RF ground.






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"Frank Gilliland" wrote in message
...
On Thu, 4 Nov 2004 20:07:21 -0500, "M-Tech"
wrote in :

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


A given length of coax runs from the radio to the antenna mount. If
the shield is not adequately grounded (RF ground) then RF will crawl
onto the outside of the shield. When that happens your coax behaves
like an antenna, having resonant and non-resonant lengths. When that
happens, different lengths of the coax will put the antenna mount at
different phase angles, therefore changing the load impedance and SWR.
There are only two solutions: Provide a good RF ground to the antenna
mount (preferred), or change the length of the coax to 'tune' the
input impedance of the antenna.

That's all assuming your radio is fixed to a good RF ground.

Yeah, check-check. I'm with ya. I was just trying to ask(albeit,
sarcastically) who the hell would loop coax through their vehicle instead of
looking for a ground problem!!! I'm also assuming that if the above case
was true, you'd NEVER get enough of a ground to get a decent(say 2:1)swr
unless you have a few hundred feet in the trunk!!

I just always was told that if you have a swr problem, it won't be fixed by
changing coax lengths.

Also, why do people have negative comments about mag mounts? Mine works
fantastic. Maybe the paint on my Passat is thin:-)

Don
313

On Fri, 5 Nov 2004 19:27:06 -0500, "M-Tech"
wrote in :

snip
Yeah, check-check. I'm with ya. I was just trying to ask(albeit,
sarcastically) who the hell would loop coax through their vehicle instead of
looking for a ground problem!!! I'm also assuming that if the above case
was true, you'd NEVER get enough of a ground to get a decent(say 2:1)swr
unless you have a few hundred feet in the trunk!!


More than you might think: http://tinyurl.com/5z49m


I just always was told that if you have a swr problem, it won't be fixed by
changing coax lengths.

Also, why do people have negative comments about mag mounts? Mine works
fantastic. Maybe the paint on my Passat is thin:-)


I don't know if you have ever run anything else, but I have and the
difference is significant.






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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

He never said that a poor RF ground could be corrected by coax length.

He said in effect that the side effects of a poor RF ground could be
reduced by a specific length of coax.

wrote in message
news


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

He never said that a poor RF ground could be corrected by coax length.

He said in effect that the side effects of a poor RF ground could be
reduced by a specific length of coax.

He sure did. He said mag mounts have a poor ground. He said the length of
the coax can help by being "part of the ground plane"(counterpoise). I'm
simply saying you'd need a TON of coax to do that...and get a decent
swr(point of post).

Hence, length of coax(within reason, obviously)on a wilson 1000 mag mount
means diddly squat.

I'm I right, or wrong:-)

Don
313

Hence, length of coax(within reason, obviously)on a wilson 1000 mag mount
means diddly squat.

I'm I right, or wrong:-)

Don
313

I'd bet you're wrong for many installations.The only way to find out
is to take the brand new Wilson 1000 mag mount that you'll purchase to
make your point and cut the coax.. If you are so positive that your
theory is absolute then you should not have any problem cutting the
18' length to the shortest length possible before you ever key up