Furuno Radar Cable Junction Box? - SailNet Community

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  #1  
Old 03-12-2006
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Furuno Radar Cable Junction Box?

It was necessary to cut the signal cable for my Furuno Radar (Model 1720) to remove the mizzen mast. The cable was jammed and the crane was on it's way. The Owner's Manual says 'no splices allowed' but goes on to say ".. a junction box may be installed at the base of the mast, under the floorboards. (sic) The junction box must be watertight and the wire breakout must be kept as short as possible."

Has anyone done this?

Terry
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Yes, it's been done.
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Old 03-12-2006
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We have had this done twice

Terry, no splices means wire-to-wire splices. Radars are fouled up by two things when it comes to cable splices. The impedance/resistance/continuity of each splice is different and not enough attention to the length of the splice can induce timing errors.

The junction box is simply a dry enclosure for a high quality, low resistance terminal block. With each wire cut and stripped with the proper tool and a connector properly applied, the electrical and time delay issues are avoided. We also put silica gel packets in the box, and we covered the connections with dry silicon lube. The first radar was working 10 years after we did this (same reason as you). We had the current radar installed this way.

[On higher power radars with wave-guide used between the antenna and processor a terminal block won't do it]

Hopefully in the situation you describe, the wires were simply cut and sections were not taken out.

We had a technician do this both times, but I would tackle it if necessary.
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Old 03-12-2006
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Furuno Radar Cable

I cut mine for a Furuno LCD in order to mast mount the antenna without cutting a very large hole in the coachroof. I am happy with the results using a junction block and a cover, but the coax wire is difficult. The inner conductor in the coax is an extremely tiny wire and instead of being covered by poly, the poly is melted over the wire. Hence, attempts to strip the poly cuts the wire. After a couple of failed attempts, I melted the poly off and used a butane soldering iron to make the connection. Good luck.
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Old 03-12-2006
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Thanks for the advice, mateys. That small coax has been my concern all along but I will give it a go. I think I will splice the coax and use terminal blocks for the other signal wires.

Cheers and beers,
Terry
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Old 03-15-2006
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I did this for a Furuno radar about 12 yrs. ago. Used a Lewmar (as best I remember) junctions box. I put a coax connector in the coax lead (yes you can find one for that size coax, but not easily). Remember, If you had to do it once, you will probably have to do it again. Make things easily disconnectable. I have had mine apart several times, but not problems yet.
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Old 03-16-2006
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Cable splices eat up transmitting power, so avoid them if at all possible. For attachment to another piece of coax, use a high quality barrel connector (PL-258) and PL-259 connectors. Try to avoid splicing the coax bare wired. Also, consider splicing inside RFI-Conductive Plastic Enclosures, such as Hammond Manufacturing #1594RFI Series.
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Old 03-16-2006
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I agree about the need for high quality barrel connectors in this application. The problem is finding ones. This coax is really small - I have forgotten the designation of it, but it has a total thickness of about 1/8 to 3/16 thick as I remember. It is a very unusual coax. However it is carrying high power levels (for very short times), so the impedence matching of the connection is important. I think I ended up with a BNC style connector. The cited PL-258 and PL-259 connectors are for RG-8 coax at the smallest - which is lots larger than this. Try to find a designation for the cable in documentation or by looking at the cable - sometimes it is printed on the cable. Then get the appropriate connector. This will minimize power loss at the connection point.
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Old 03-16-2006
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Good news! After convincing Furuno that it was stupid to forward my question to Japan for an answer (that was because I answered a question about my location being in Thailand, though I had purchased the radar in the USA) I have now received the following answer from Furuno USA:
=============================
Thank you for contacting Furuno USA, Inc.

Hello Terry,

Since the cable is already cut I would find and use a suitable splice for the Coax, the center wires are very fragile but what I find that helps is to solder or splice a larger gauge cable to the center coax and then take that to your terminal strip/junction box, the rest of the cables should be fine.
=====================

So now we all know the manufacturer's recommendation.

Thanks again for all of the replies.
Terry
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