Ian Jackson wrote:
In message , dave
writes
Antonio Vernucci wrote:
Can I bend the long whip so it stands vertically? Should I do it?
does the downward slope of the ground plane leave a problem
unaddressed?
Although the issue may be more aesthetic than functional, I inform
you that I have a magnetic mount (built by Kathrein) that has a
swivel at the whip connection point. So, even if the mount is
slanting, you can adjust the swivel so that the whip is perfectly
vertical.
73
Tony I0JX
Rome, Italy

A 2 Meter 5/8 Wave antenna is too long for a magnet mount.

Not if the magmount is one of those which is around 7" diameter. Also,
with the one I have, the coil at the base is something like 4 turns of
1" internal diameter spring steel so, if the whip does hit something,
there's a lot of 'twang' in the system. There's almost no way that the
magnet can be dislodged.

I stand corrected. Thanks.

http://www.hamcity.com/detail.aspx?ID=786

A 2 Meter 5/8 Wave antenna is too long for a magnet mount.

Not if the magmount is one of those which is around 7" diameter. Also, with
the one I have, the coil at the base is something like 4 turns of 1" internal
diameter spring steel so, if the whip does hit something, there's a lot of
'twang' in the system. There's almost no way that the magnet can be
dislodged.

I stand corrected. Thanks.

http://www.hamcity.com/detail.aspx?ID=786

If you go to page http://www.kathrein.de/de/car/montag...ad/936127a.pdf
(the English description follows the German description) you will see the
144-MHz Kathrein antenna model K 51 17 2, which is a 5/8 wavelength
magnetic-mount antenna with a swivel. The whip is 1.38 m long (about 4.6 feet)
and the magnet diameter is 95mm (about 3.7 inches). The tuning coil is located
inside the mount..

That antenna is very common in Europe; they sell it since more than 30 years.
Please note that 57% of the German highways have no speed limit (see
http://en.wikipedia.org/wiki/Speed_limit) and it is not uncommon to see the big
Mercedes or BMW running at more than 120 mph).

Another 144-MHz 5/8 wavelength antenna I have has a magnet of comparable
diameter.

73

Tony I0JX

Ken,
If you consider how much movement that there is in a whip in a mobile
situation, the 20 deg will not make much difference to it, I bent mine a
fraction more, and it made little difference to the VSWR or the performance.

John VK2KC

"Chevy454" wrote in message
...
I want to put my 2M 5/8-wave mag-mount on the trunk lid, which slopes
down at 20 degrees. I am concerned that most of my signal is going
into the ground or outer space.

Can I bend the long whip so it stands vertically? Should I do it?
does the downward slope of the ground plane leave a problem
unaddressed?

Ken KC2JDY

On Fri, 30 Jan 2009 12:17:57 -0500, Chevy454 wrote:

I want to put my 2M 5/8-wave mag-mount on the trunk lid, which slopes
down at 20 degrees. I am concerned that most of my signal is going
into the ground or outer space.

Not that big of a deal. What is (1 - the cosine of 20 degrees)?


Can I bend the long whip so it stands vertically? Should I do it?
does the downward slope of the ground plane leave a problem
unaddressed?

Ken KC2JDY

It will probably upset the grip of the magnetic mount a bit. It will
probably give you a curved radiator. Not much effect, try it if you
like.

In message , JosephKK
writes
On Fri, 30 Jan 2009 12:17:57 -0500, Chevy454 wrote:

I want to put my 2M 5/8-wave mag-mount on the trunk lid, which slopes
down at 20 degrees. I am concerned that most of my signal is going
into the ground or outer space.

Not that big of a deal. What is (1 - the cosine of 20 degrees)?


Can I bend the long whip so it stands vertically? Should I do it?
does the downward slope of the ground plane leave a problem
unaddressed?

Ken KC2JDY

It will probably upset the grip of the magnetic mount a bit. It will
probably give you a curved radiator. Not much effect, try it if you
like.

Indeed. At speed, a nice, whippy stainless steel whip curves a scimitar.
Very pretty! But you'd have to be approaching Mach 1 to dislodge a 7"
limpet magmount.
--
Ian