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Old 22-11-2012, 14:13   #1
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Masthead power cable

I have wooden spars on my boat. All cables used to run inside of the mast but now the connection is broken. There is no way I can pull these cables and install new ones.
Looks like I will have to run it outside. To minimize the number of cable would it be possible to use the VHF antenna cable to run the power to the masthead. I guess I would have to use some inductors at the connection to block the rf components. All control connections - wind vane, light switching etc. would run wireless (xbee or nrf24l01+). What do you think about this idea, any suggestions ?
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Old 22-11-2012, 14:29   #2
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Re: Masthead power cable

At the end of the day it will probably be easier to just run the new wires, but this could work. You will likely need DC-blocking capacitors in addition to the inductors and will need to be very careful with the design and physical layout of the filters.

What kind of coax do you have, and what is the length? RG-8 or similar might support an incandescent tri-color, but with skinny RG-58 type coax a lower-current LED fixture may be required. You can perhaps wire a polarity-control switch to let you have a combined tri-color / anchor light at the masthead.
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Old 22-11-2012, 14:35   #3
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Re: Masthead power cable

I'm using LMR400 cable . Also the masthead lights are all LED.
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Old 22-11-2012, 15:04   #4
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Re: Masthead power cable

The LMR400 has about 1 milli-Ohm per foot resistance, so DC loss shouldn't be an issue. Have you figured out how to put together the DC / RF diplexer? I think you will need capacitors because most VHF whips are essentially D.C. shorts. I don't know about the radio port, but I wouldn't be surprised if it was a D.C. short as well.

I'm not sure I would choose to use xbee or some similar control at the masthead, just because it's exposed to weather and hard to access. There's something to be said for the reliability of well-spliced and protected wiring. But that's just a prejudice of mine.
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Old 22-11-2012, 16:17   #5
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Re: Masthead power cable

You will likely need a DC blocking device at each end as the antennas (and receivers?) tend to look grounded to DC. Otherwise it can work. Since you are getting complicated you can increase current capacity by raising the voltage or applying AC to the coax.
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Old 22-11-2012, 18:49   #6
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Re: Masthead power cable

Check out the common TV masthead amplifier setups to get some clues how to send power up the coax like you want to do. Inductor and capacitor needed at both ends to pass the DC and vhf (AC) signal respectfully.

This is a solution that reduces cabling aloft and easily achieved. The two electronic components reqd at the top are so small that is just as easy to totally encapsulate in sealant for moisture protection which is essential for the coax anyway.

Excellent suggestion from Paul re polarity change between anchor and sail mode lights -all thats needed at the top are two extra diodes -actually only one extra if you utilize one of the LED's as one of the polarity diode.

Have you thought of changing to non mast installed nav lights? Only difficulty is with the steaming light which needs to be 2.5m above the side lights but this is easier to do on the mast at a lower height perhaps combined with spreader light. For the vhf, being line of sight, height obviously does help but practically speaking I'm not so convinced that the extra range is worthwhile to have the antenna go all the way to the top. I'm currently using a J pole vhf antenna mounted off the arch and have no wires up to the top. If I wanted the extra hight this is what I'd do: Mount the antenna on a " travelling car" that slides up the backstay using cable ties for the coax. Hauled up with the main halyard with a "ring" around the stay and a temporary 'downhaul' rope and retained at the top similar to a halyard lock fitting. To bring down (for replacing the cable ties that would not last) simply run up the halyard and ring up to release the halyard lock. No dedicated halyard necessary and easy to maintain without climbing the mast.
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Old 22-11-2012, 19:36   #7
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Re: Masthead power cable

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Originally Posted by otya View Post
-actually only one extra if you utilize one of the LED's as one of the polarity diode.
Oops!! actually no extra diodes are required for a LED masthead light which is rewired internally with one diode reversed, or at least 4 diodes and resulting voltage drop if modifying a 3 wire sealed unit

I just realised I had already made this suggestion way back -but the halyard lock concept is a worthy improvement! comments?
"QUOTE=otya;441599" EDIT Two quoted posts dont seem to work
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Old 22-11-2012, 20:23   #8
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Re: Masthead power cable

Or just run a small conduit up the mast for all the wires?
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Old 22-11-2012, 22:53   #9
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Re: Masthead power cable

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Or just run a small conduit up the mast for all the wires?
Ditto! Then its done properly.

Though I am somewhat perplexed as to why there is no way to Mouse replacement cable through.
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Old 22-11-2012, 23:15   #10
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Re: Masthead power cable

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Originally Posted by ozskipper View Post
Ditto! Then its done properly.

Though I am somewhat perplexed as to why there is no way to Mouse replacement cable through.
The cable has been broken by a crane operator when they lowered the mast . He pulled out around 3m of the cable from one side . The rest of the cable is still inside but is jammed really well and I cannot remove it. This is a boxed mast construction with a few solid section around the spreaders and other hardware. To install a new cable I would need to drill a new hole through the solid sections which , I guess is almost impossible without opening the mast.
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Old 22-11-2012, 23:19   #11
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Re: Masthead power cable

in that case, its the crane guys responsibility. Easy said I know, as they will have waivers in place of course.

I am still confused, why the old cable cant even be left inside the mast and new one run through new holes. isnt the mast hollow?
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Old 23-11-2012, 00:50   #12
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Re: Masthead power cable

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Originally Posted by ozskipper View Post
in that case, its the crane guys responsibility. Easy said I know, as they will have waivers in place of course.

I am still confused, why the old cable cant even be left inside the mast and new one run through new holes. isnt the mast hollow?
Oops,, I mised the bit where you said there were some solid sections inside. My bad. Back to the ducting!!
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Old 23-11-2012, 04:26   #13
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Re: Masthead power cable

What are your carpentry skills like? Access the area through the mast wall, replace wiring,
fit filler block.
Modern adhesives will make a strong repair.
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