Dipole keeps melting?



I've got a multi-band inverted V trap dipole antenna which as my first HF
antenna seems to working fine, I like the fact that can get away without a
tuner on most bands.



However I've just started getting into 80meters and the tip of the dipole
keeps melting the guy rope isolator hence the dipole leg falls to the
ground, only running 200watts, the antenna is rated for 1kw.



Everyone suggested its high SWR but not according to 3 different SWR meters
(1.1:5) I always use a tuner built into the amp to give the perfect VSWR but
after 10 seconds the melting starts and the VSWR starts to increase..



Any ideas?

Are you just tying the wire to the nylon rope? Perhaps you need a glass
or ceramic insulator between.

Alan AB2OS


Andy wrote:

Dipole keeps melting?

I've got a multi-band inverted V trap dipole antenna which as my first HF
antenna seems to working fine, I like the fact that can get away without a
tuner on most bands.

However I've just started getting into 80meters and the tip of the dipole
keeps melting the guy rope isolator hence the dipole leg falls to the
ground, only running 200watts, the antenna is rated for 1kw.

Everyone suggested its high SWR but not according to 3 different SWR meters
(1.1:5) I always use a tuner built into the amp to give the perfect VSWR but
after 10 seconds the melting starts and the VSWR starts to increase..

Any ideas?

You are using a rope that absorbs RF energy and has a low temperature
melting point. There is a very high voltage electric field at the end of a
dipole which gets absorbed by the rope causing it to melt.

Spend more money on better quality rope. Stay away from 'poly' (or
polystyrene rope). Nylon is good (but stretches). Dacron is considered
better. Natural fiber ropes are very good (such as hemp). In general, if
it doesn't cleary identify what type of plastic it is, don't buy it.

I don't think an insulator would make much difference for this problem but
you should be using one anyway.

--
Jim
N8EE

to email directly, send to my call sign at arrl dot net
"Andy" wrote in message
...
Dipole keeps melting?



I've got a multi-band inverted V trap dipole antenna which as my first HF
antenna seems to working fine, I like the fact that can get away without a
tuner on most bands.



However I've just started getting into 80meters and the tip of the dipole
keeps melting the guy rope isolator hence the dipole leg falls to the
ground, only running 200watts, the antenna is rated for 1kw.



Everyone suggested its high SWR but not according to 3 different SWR
meters
(1.1:5) I always use a tuner built into the amp to give the perfect VSWR
but
after 10 seconds the melting starts and the VSWR starts to increase..



Any ideas?

I don't think an insulator would make much difference for this problem but
you should be using one anyway.

--
Jim
N8EE

Makes BIG difference. You have high RF volatge point at the ends, you need good
quality insulator that doesn't absorb water (like rope) or melt under RF. It
helps to make small loop of wire, so it is terminated in "capacitor" plate
rather than sharp wire end (had that problem with balloon vertical).
Situation gets worse in salty air environment, where rope becomes conductive
when soaked with moisture and salt. Loop made of plastic ties works OK as
insulator, rope tied directly to the end of wire is a NO-NO!

Yuri,
www.K3BU.us
www.computeradio.us - home of Dream Radio One

Andy wrote:
However I've just started getting into 80meters and the tip of the dipole
keeps melting the guy rope isolator hence the dipole leg falls to the
ground, only running 200watts, the antenna is rated for 1kw.

What happens at the tips of the dipole has virtually nothing to do with the
SWR at the transmitter. The voltage at the ends of the dipole for 200w will
be in the ballpark of 600 volts RMS, 1600 volts peak-to-peak.

What are your insulators made of? Change to glass and the problem will
probably go away. If you are in a salty environment near an ocean, that
will aggravate the problem. Sounds to me that you simply need better
quality insulators.
--
73, Cecil http://www.qsl.net/w5dxp



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On Tue, 11 May 2004 10:38:06 +0200, "Andy"
wrote:

Dipole keeps melting?





Any ideas?


Check the websites of places like RF Davis, The Wireman or Radio
Works. They sell rope that is appropos to antenna use -- it stands up
to the outdoor environment, and doesn't stretch too much. They also
sell end insulators for antennas -- sounds like you may not be using
any -- the wire shouldn't tie directly to the rope.

Bob
k5qwg

You're hitting a current node out at the ends of the wire. You could add
some wire to the 80M elements, but if the antenna is working properly, your
better option would be to find better end insulators. Ceramic dog-bone
insulators are only a couple of bucks apiece...

73,
Mike KI6PR
El Rancho R.F., CA

"Andy" wrote
I've got a multi-band inverted V trap dipole antenna which as my first HF
antenna seems to working fine, I like the fact that can get away without a
tuner on most bands.



However I've just started getting into 80meters and the tip of the dipole
keeps melting the guy rope isolator hence the dipole leg falls to the
ground, only running 200watts, the antenna is rated for 1kw.



Everyone suggested its high SWR but not according to 3 different SWR
meters
(1.1:5) I always use a tuner built into the amp to give the perfect VSWR
but
after 10 seconds the melting starts and the VSWR starts to increase..



Any ideas?

"Andy" wrote in message ...

However I've just started getting into 80meters and the tip of the dipole
keeps melting the guy rope isolator hence the dipole leg falls to the
ground, only running 200watts, the antenna is rated for 1kw.

Already some time ago I experienced the same thing, as I did not want
to use ceramic or glass insulators which would make my antenna
system(s) even more visible.

Now I am always using transparent 'Bic' ball-points for which I have
removed the the 'ink-cartridge'. Using this tranperent enclosure, on
both sides (using the small nail and the soldering iron) I melt 2
holes. At one I connect the antenna wire and at the other I connect
the guy rope. After using this solution I did not have these problems
any more, even using considerable power.

I do not know if these 'Bic' ball-points are available in the US, but
overhere in Europe they are widely used.
For an example picture I found the below url on the Internet:
"http://www.findaproperty.com/cgi-bin/story.pl?storyid=5985%20-%2015k"

Arie.

p.s. I almost forgot: All this has nothing to do with SWR

Thanx for all your help and answers, the bic pen seems to work will again
later tonight hopefully get me through to next week when the new isolators..

Thankyou

a.



However I've just started getting into 80meters and the tip of the
dipole
keeps melting the guy rope isolator hence the dipole leg falls to the
ground, only running 200watts, the antenna is rated for 1kw.

Already some time ago I experienced the same thing, as I did not want
to use ceramic or glass insulators which would make my antenna
system(s) even more visible.

Now I am always using transparent 'Bic' ball-points for which I have
removed the the 'ink-cartridge'. Using this tranperent enclosure, on
both sides (using the small nail and the soldering iron) I melt 2
holes. At one I connect the antenna wire and at the other I connect
the guy rope. After using this solution I did not have these problems
any more, even using considerable power.

I do not know if these 'Bic' ball-points are available in the US, but
overhere in Europe they are widely used.
For an example picture I found the below url on the Internet:
"http://www.findaproperty.com/cgi-bin/story.pl?storyid=5985%20-%2015k"

Arie.

p.s. I almost forgot: All this has nothing to do with SWR

"Mikey" wrote in message
...
You're hitting a current node out at the ends of the wire. You could add
some wire to the 80M elements, but if the antenna is working properly,
your
better option would be to find better end insulators. Ceramic dog-bone
insulators are only a couple of bucks apiece...

Of course there is a current node at the end.

The end of the dipole is open circuit isn't it? Unless the laws of physics
have changed since I've been in school, electrons can not flow through an
open circuit. There will always be a 'current node' at the end of a dipole
regardless of the length. There will also be a high voltage electric field.
With high enough RF power the electric field can be strong enough to cause
arcing and corona. The strength of the field will depend on the shape of
the end of the dipole (rounded vs pointed), as I was properly chastised for
forgetting on my other post.


--
Jim
N8EE

to email directly, send to my call sign at arrl dot net