Attaching coax to insulated backstay - SailNet Community
 
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post #1 of 6 Old 07-10-2004 Thread Starter
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Attaching coax to insulated backstay

Anyone have any advice/tips etc. for attaching the coax to an insulated backstay used for HF (ham) SSB?

When you get an insulated backstay made is there a ''special'' lug, (etc.) available that could be attached at the time of fabrication?
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Attaching coax to insulated backstay

Using a coax to feed an insulated backstay antenna is not really a very practical idea. It can be done, but the length of the backstay antenna must be a 1/4 wavelength or an odd multiple 1/4 wavelength of the frequency you wish to use for it to work properly.
Since most SSB operation is dependent upon the ability to use several(or many) frequencies, trying to use coax on a fixed length antenna is very limiting regarding the frequencies you might be able use.

A better arrangement is to use coax from the transmitter to an antenna tuner. From the antenna tuner an insulated wire to the backstay antenna is appropriate. The antenna tuner has the ability to tune the backstay antenna to look like it is a 1/4 wavelength of whatever frequency you wish to operate on.
Some antenna tuners can compensate for the impedance mismatch between the physical antenna length and the coax impedance at the backstay, but in my opinion, an insulated wire from the tuner to the backstay is a much cleaner installation.

Jim
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post #3 of 6 Old 07-10-2004 Thread Starter
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Attaching coax to insulated backstay

Being a ham radio operator myself I understand the issues of matching impedances of what is essentially an end fed antenna. i.e. I agree a tuner is necessary.

However my question was simply more how to properly attach the feedline ''mechancially'' to the backstay

When having a insulated backstay fabricated, is there an optional lug/tab/etc. available I should request to attach/solder the feedline to the backstay?

I''ve heard some just use a ''U'' clamp to clamp the feedline to the backstay wire but I''d think that would be very lossy/inefficent, especially in a salt-water enviornment.
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Attaching coax to insulated backstay

Sorry, you never know who you are addressing on some of these questions!

Your concern re the corrosion/lossy connection is valid. I am unaware of any special connectors for the job. The only thing I can think of is encapsulating whatever connection is made to keep moisture away from the connection. Maybe some Lifeseal caulk?

Jim K6CWI
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post #5 of 6 Old 07-11-2004
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Attaching coax to insulated backstay

Exposed HF feedline connections:
For your consideration:
1. Use an anti-oxidant compound* on the cable, stay, and lug, then seal overall.
* Ideal “No-Alox”, Burndy “Penetrox”, GB “Ox-Guard”, etc.
2. Use a Tin-Plated Copper alloy “Split-Bolt” Connector, such as: Burndy type “KSU” c/w “SU” Cover or equal. See pages 4 & 5 at:
http://www.fciconnect.com/pdffiles/brochures/Section_A_2003MC-Mechanical.pdf

3. Separate the feedline from the stay (inductance in parallel conductors). Cut 2" pieces of small diameter rigid plastic tubing/pipe with a larger diameter drill bit. This leaves the cut ends with a curved concave profile (that matches the stay & cable diameters). Insert a tie-wrap through the tube, around the stay, back through the tube, and around the cable & draw tight. You have a 2" stand-off”.

I''ve never had any customer complaints (/w above), but I''m not a HAM, so my experience is second hand.

Gord
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post #6 of 6 Old 07-11-2004 Thread Starter
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Attaching coax to insulated backstay

Thanks, That''s just the info I was looking for.

I''m puzzled though why backstay insulators don''t already have some sort of integrated lug/tab/etc. on one side of the insulator for the purpose of attaching a feedline to the stay wire. Thus, you would orient the lug/tab side of the insulator toward the section of backstay to be used as the antenna.
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