Running VHF coax in Kenyon mast wiring track

[Nick J]

Has anyone successfully replaced a VHF coax in their Kenyon mast wiring channel?

I've been chasing some VHF issues since installing the Vesper Cortex and now I'm at the point where I think the coax should be replaced. I've replaced all the connectors, but the center conductor has some corrosion that I'm not able to cut out because there's not enough slack.

Before:




After (I had to replace the section going back to the nav desk after I took this picture because I noticed the crimp wasn't correct after looking at this pic)

I thought it would be somewhat straight forward because I was able to pull the existing RG-59 up the mast to gain slack when I replaced the antenna and put a new PL-259 connector on the end, but now I'm second guessing that assumption.

Yesterday, I put an endoscope in the wiring exit hole at the base of the mast and realized the existing cable is run down the wiring channel behind the sail track. It exits the channel a few inches above the base of the mast and comes out on the port side of the mast. I'm not sure what's happening at the top. All I can see is is enters the mast at the top of the masthead, but I'm not sure how it gets from there to the wiring channel. There wasn't that much resistance, but I'm planning on replacing the RG-59 with RG-213. Any advice would be greatly appreciated!

 

[Nick J]

Now that I have the mast out for a full rebuild, I thought it would be good to follow up this for anyone else wondering about this in the future. I think it may be possible to pull a new coax through the wiring channel with the mast up, but a lot of variables have to be in place:

• The cable can't be secured anywhere in the mast - If yours is loose like mine was, you may have a chance, but this isn't a good way to install a new cable because there's nothing taking the vertical strain of weight of the cable. I used multiple cable anchors at the top and added globs of silicone every 4' to reduce cable slap at anchor. There's no way anyone would be able to pull a new cable in my mast now, but it should be much quieter at anchor.
• Entrance and exit points in the channel are tight and can be rough - even if you are able to get the new cable pulled through, there's a good chance you would damage the outside coating and potentially ground the shield on the mast or put a bend in the cable that would reduce the insulation between the center conductor and the shield.
• the transition from the old cable to the new cable would have to be extremely smooth to avoid catching on the existing wires or exit points

Top exit before I added heat shrink protection and cable clamps:


Exit at the bottom of the channel:



Silicone globs:

 

[bgary]

I think it would be darn near impossible to pull coax through with the mast up.

I did mine with the mast out, as you did. I did a drip-loop outside the mast at the top just below the antenna mount. I secured the cable with a couple of cable ties inside the mast at the top to carry the load (yeah, I know that'll make it impossible to pull new cable with the mast up, but I didn't think that was ever a viable approach anyway).

One note - too late to help you, but might help others - my HAM buddies highly recommended LMR-400 "ultraflex" coax, very good spec and since it is designed for HAM antennae out in the weather, pretty good moisture resistance. I bought a sample to play with and found it to be too thick (0.400" in diameter), and very stiff - bend radius is something like 4", which would make it hard to (e.g.) route it from some of the corners between mast heel and nav stations. What I found was that they also make LMR-240, which has nearly as good a spec, is much thinner (0.240"), and much more flexible. FWIW

B

 

[Nick J]

I chose Rg 213 because it has tinned copper and slightly better attenuation than LMR 240. In hindsight, I would go with LMR 240 because it's lighter and the difference in attenuation is negligible. I also ended up using every bit of the minimum 2" bend radius at the top of the mast. Having a little more flexibility would be nice.