SSB antenna question

[Ayesha]

I have a coax lead coming from the top of an ICOM ATU. This has a core
and a screen. It comes up through the deck to an insulated backstay.
Question : should I ignore the screen, and simply cut it back? Or
should I connect the screen at the ATU end to the ship's earth?

thanks

 

[Woody]

I have a coax lead coming from the top of an ICOM ATU. This has a core
and a screen. It comes up through the deck to an insulated backstay.
Question : should I ignore the screen, and simply cut it back? Or
should I connect the screen at the ATU end to the ship's earth?

thanks

There have been a number of threads about your question. Try searching
google/groups.

BTW, in the following, "ground" = "earth".

The short and over simplified answer is to connect the shield braid
(screen) to the antenna tuner ground. At the antenna end, if feasable,
the shield could/should be connected to the stay on the other side of
the lower insulator.
But... The coax is likely to become part of the radiator and the
tuner/antenna will likely perform less well than with a more "ideal"
configuration.

Idealy the tuner should connect to the backstay with unshielded high
voltage wire (like spark ignition wire - I forget the exact
designation). This *will* be part of the radiating antenna and should
be kept clear of people, other wiring/electronics, and metal. This means
mounting the tuner near the antenna feed - and very near a good ground.
The ground from the tuner should be as straight and short as possible to
ship's ground and water ground.

Ferrite sleeves can be placed over the coax feeding the tuner (at the
tuner) to help minimize stray radiation from the line between the radio
and tuner.

Woody

 

[Glenn Ashmore]

Pull out the coax and replace it with GTO-15 high voltage wire. Your
antenna begins at the terminal on the tuner and coax can cause a lot of
loss.

 

[Me]

There have been a number of threads about your question. Try searching
google/groups.

BTW, in the following, "ground" = "earth".

The short and over simplified answer is to connect the shield braid
(screen) to the antenna tuner ground. At the antenna end, if feasable,
the shield could/should be connected to the stay on the other side of
the lower insulator.
But... The coax is likely to become part of the radiator and the
tuner/antenna will likely perform less well than with a more "ideal"
configuration.

Idealy the tuner should connect to the backstay with unshielded high
voltage wire (like spark ignition wire - I forget the exact
designation). This *will* be part of the radiating antenna and should
be kept clear of people, other wiring/electronics, and metal. This means
mounting the tuner near the antenna feed - and very near a good ground.
The ground from the tuner should be as straight and short as possible to
ship's ground and water ground.

Ferrite sleeves can be placed over the coax feeding the tuner (at the
tuner) to help minimize stray radiation from the line between the radio
and tuner.

Woody

I would try and correct the above, but it is Sunday, and I don't work on
Sundays, and correcting the above would be an an hours of work........


Me advice is only as good as what you paid for it............

 

[Manlio Laschena]

Followup to msg on Sun, 17 Oct 2004 11:20:20 GMT, Woody
<[email protected]> :
(Original msg on bottom)

The name is GTO15, you can find it also on the WestMarine online
sales.

Therefore: no shield but 15000 V insulated cable.

In case the non insulated part of the backstay is connected to ground,
better is to put some spaced insulated sticks to held the GTO15 about
7 cm far away from the backstay (hope you can understand my bad
english), where the cable goes down to the deck.

Ciao Manlio

dealy the tuner should connect to the backstay with unshielded high
voltage wire (like spark ignition wire - I forget the exact
designation)

Manlio Laschena
s/y Amarose
http://Delphi-Jedi.org

 

[Ayesha]

thanks everybody for your help. Much appreciated

 

[Martin]

Pull out the coax and replace it with GTO-15 high voltage wire.

Where in the Uk would I buy GTO-15 wire?

 

[Ayesha]

Where in the Uk would I buy GTO-15 wire?

Good question. Just spoken to Merlin ( great experts on marine cabling)
and they've never heard of it. Clearly it has another name here in the
UK. If I discover, I'll post here.

 

[Glenn Ashmore]

GTO-15 is primarily used in wiring neon signs and oil burner igniters. It
is a single 14 gauge stranded conductor incased in a thick Polyethylene or
PVC insulation. A little over 1/4" in diameter.

Check with a neon sign shop. They will probably give you 15' or at least
sell it sans the "marine" label for a lot less than a chandler will. It is
exactly the same thing.

BTW, it should not be taped directly to the lower uninsulated section of the
backstay. Mount it with some 2-3" standoffs. Some very neat standoffs can
be made from 1/2" plastic conduit. Drill it the diameter of the backstay
every 2" and cut it apart through the holes. Use black zip ties through the
conduit and around the stay and wire to mount them.

Another hint. Run the wire above the connection point and then back down to
the clamp. That will keep water from soaking under the insulation and
causing corrosion.

I saw a really nice installation at the Annapolis show. It was a continuous
black plastic extrusion that had a tube on one side for the wire to run
through and snapped onto the stay on the other. Unfortunately nobody could
tell me where it came from.

 

[John Proctor]

Good question. Just spoken to Merlin ( great experts on marine cabling)
and they've never heard of it. Clearly it has another name here in the
UK. If I discover, I'll post here.

Belden makes HV leads (rated at 35KV, 60KV or 80 KV dc breakdown) part
numbers are: 8869, 9867 and 8866. The 8866 type wire is 18 AWG
stranded. Any cable supplier of note should be able to supply a type
number equivalent.

 

[Doug Dotson]

It is OK to parallel the GTO-15 to the lower part of the backstay
as long as the lower portion of the backstay is not grounded (ie part
of a bonding system). If the lower part of the stay cannot be isolated
for some reason, then the standoffs are requires.

Doug
s/v Callista