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-   -   Testing and tuning mobile antennas (https://www.radiobanter.com/antenna/1472-testing-tuning-mobile-antennas.html)

Patrick Gardella March 26th 04 02:40 PM

I am trying to get an SWR that will actually read on my SWR meter. :) Right
now it's off the scale on 10m and 6m. It's around 5 or 6 on 2m. I don't have
a meter for 70cm.

FWIW this antenna is a quad band: 10m/6m/2m/70cm . My dual band (2m/70cm)
works just fine.

Patrick

"Steve Nosko" wrote in message ...
Perhaps I should enter the text BEFORE hitting the send button, eh?

Doc has a good idea here with an "external" ground/counterpoise ae a
test.

However, I would ask: How are you determining when it is tuned? What
are you using to determine if it is tuned?

I don't think this talk about connecting braid to the FRAME is good.
The antennas are usually designed to have a ground-plane right at the base
of the antenna and a length of braid can be easily more than a quarter wave
at 2M and 440 and the frame is far from the antenna base. With plastic
paneled cars it is common to put some sort of foil or plate inside the body
to provide the ground plane.

--
Steve N, K,9;d, c. i My email has no u's.

"Steve Nosko" wrote in message
...

"'Doc" wrote in message ...


Patrick,
Sorry, tuning the antenna 'off of' the car won't work
(miracles do happen, but don't count on it). The most likely problem is
as you thought, a not so good 'ground', but maybe not. Does
anything you do change the tuning of the antenna at all? Maybe not get
it to where you want it (freq.), but does change it's resonant
freq? If not, then there's something else 'going on' besides the
inadequate
grounding/counterpoise. Make sure you have a good connection
through the mount, no shorts/opens except as they should be, etc. And
you probably should do something about the grounding/counterpoise,
maybe clip a wire to the base of the mount as a counterpoise to see
what difference it makes (just lay it on the surface of the car for
now). The length of the counterpoise isn't that critical, but too long
is 'better' than too short. Changing the location of the mount is
also something you might try.
Good luck...
'Doc




Stephen Cowell March 27th 04 04:46 AM


"Patrick Gardella" wrote in message
om...
Thanks, Doc.

I don't have an antenna analyzer, so I can't check the resonant
freq that way. I was relying on an SWR meter (my shack one).
Nothing at all changes when I adjust the antenna. SWR doesn't
move. I may try to borrow an analyzer from someone to check
that out.

The mount and cable are fine. Just got a new 2m/70cm dual
band antenna to use until I can get the UHV-4 working.
It has a nice SWR of around 1.3 on 2m.

On the UHV-4 antenna, I can't get below an SWR on 2m of
around 5 or 6, even though it's supposed to be ground
independant (1/2 wavelength). I can't adjust the 2m/70cm
at all anyway. It's fixed.


Verify that the screw-off connector (NMO or 259) is actually
making contact... what you're describing (super high swr on
HF, high swr on 2m) points to a piece of unterminated coax
with no antenna on the end! Try reading swr without the UHV4
connected... same reading? Bad connection...
__
Steve
KI5YG
..



Patrick Gardella March 27th 04 10:23 PM

There is a reason why people post on usenet. They get answers.

And Steve, you have solved a years worth of puzzling and tweaking.
The SWR was the same with or without an antenna. The antenna
is bad. From the PL259 to the antenna I get no connectivity.
I just tested it with a VOM.

Why is it that the simple things are the last things you check.

Now does anyone know how to take a UHV-4 apart? ;)

73,
Patrick N3EO

" Stephen Cowell" wrote in message . com...
"Patrick Gardella" wrote in message
om...
Thanks, Doc.

I don't have an antenna analyzer, so I can't check the resonant
freq that way. I was relying on an SWR meter (my shack one).
Nothing at all changes when I adjust the antenna. SWR doesn't
move. I may try to borrow an analyzer from someone to check
that out.

The mount and cable are fine. Just got a new 2m/70cm dual
band antenna to use until I can get the UHV-4 working.
It has a nice SWR of around 1.3 on 2m.

On the UHV-4 antenna, I can't get below an SWR on 2m of
around 5 or 6, even though it's supposed to be ground
independant (1/2 wavelength). I can't adjust the 2m/70cm
at all anyway. It's fixed.


Verify that the screw-off connector (NMO or 259) is actually
making contact... what you're describing (super high swr on
HF, high swr on 2m) points to a piece of unterminated coax
with no antenna on the end! Try reading swr without the UHV4
connected... same reading? Bad connection...
__
Steve
KI5YG
.


Dave Shrader March 27th 04 11:22 PM

Patrick Gardella wrote:

There is a reason why people post on usenet. They get answers.

SNIP

Why is it that the simple things are the last things you check.


SNIP ... Wrong comment!! The Problem item is ALWAYS the last thing you
check!!! I've retired from engineering which included a four year
sojourn into professional photography. My medium format camera is/was
defective. I check and replaced the battery that runs the shutter. Still
defective so off to the repair shop. I received a call from the repair
shop yesterday, Friday, describing the defect and requesting approval to
repair. ???Are you ready??? The replacement battery was defective!!!!

I'm red faced!! I'm also $85 poorer for the want of a $3 lithium battery
:-) or :-(

Moral[s] to the story: It's always the last thing ... It's always the
simplest thing ... It's always the most embarassing thing ... etc.

W1MCE


Cecil Moore March 27th 04 11:34 PM

Dave Shrader wrote:
Moral[s] to the story: It's always the last thing ...


It's a no-brainer, Dave. When one diagnoses the problem, one stops
looking. One would be stupid to continue after the "last thing". :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Richard Clark March 27th 04 11:39 PM

On 27 Mar 2004 14:23:33 -0800, (Patrick Gardella)
wrote:

Now does anyone know how to take a UHV-4 apart? ;)


Hi Patrick,

Before you do that (what would you fix?); confirm your reading with a
load in its place (terminate the connection).

73's
Richard Clark, KB7QHC

Stephen Cowell March 28th 04 02:11 AM


"Richard Clark" wrote in message
...
On 27 Mar 2004 14:23:33 -0800, (Patrick Gardella)
wrote:

Now does anyone know how to take a UHV-4 apart? ;)


Hi Patrick,

Before you do that (what would you fix?); confirm your reading with a
load in its place (terminate the connection).


Glad to hear my psychic powers are still up to snuff... :)

But make sure that the connection is working before
you take the antenna apart... you may be able to bend
a spring (NMO) or tweak some contact leaves (259)
and get the thing working right! Sometimes connectors
have thread problems that prevent them from bottoming
properly when screwed on.... check all these things.
Make sure there's no little piece of plastic over the
important bits, stuff like that. Check for a broken center
conductor... trunk lip mounts have been known to
do this to coax, and the bigger antenna may be pulling
the connection apart.
__
Steve
KI5YG
..




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