VHF antenna coax feed INSIDE a conduit?

Machria

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Hey folks,
I’m in the middle of installing a new setup, and am wondering if what I’m about to do will have any detrimental affects on the system. Installing a triband antenna (diamond x6000a). It will be mounted via a 10’ 1 1/2” conduit pipe (aluminum) on the side of my house 35’ up. I’m planning on running the LMR400 coax inside that 10’ section of pipe, out the top and back down 1’ (in a loop) to connect to the N connector/feed point of the antenna which will be mounted to the top 1’ of the conduit via the normal u bolts.

I’m wondering if there will be any loss or other issues caused By running it inside the 10’ of conduit? I would think it would not, but possibly an affect on impedance or something?

For reference, I want to run it inside the conduit because I live in a high wind area (basically on the ocean/coast) and I don’t want the cable banging, rattling... against the conduit in the wind (like the rigging on sailboats often do).
 

RFI-EMI-GUY

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Should have no problem running inside a conduit. It is done all the time. Be careful of maintaining bend radius of the loops, and avoid chafing the coax on the conduit opening. On my discone mounting pipe, I have used plastic "wire loom" to cover the coax and taped securely in place. But be sure to use UV resistant tye wraps at top and bottom to make sure the weight of coax does not pull itself tight,
 

ka3aaa

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thats why they make uv rated tie wraps that resist uv rays. also you can use scotch 33 electrical tape which holds up very well outside.
 

mmckenna

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Will not impact performance.

I'd suggest a proper weather head at the top to keep crud out and make for a nice transition at the top.

UV rated (black) ty-wraps will work if you want to run it on the outside of the mast. They won't fall apart in the sun and will keep the cable from slapping around.
 

Machria

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Should have no problem running inside a conduit. It is done all the time. Be careful of maintaining bend radius of the loops, and avoid chafing the coax on the conduit opening. On my discone mounting pipe, I have used plastic "wire loom" to cover the coax and taped securely in place. But be sure to use UV resistant tye wraps at top and bottom to make sure the weight of coax does not pull itself tight,
Thanks. I wrapped the portion of coax that will contact the conduit opening (top and bottom of pipe) with the atomic tape (coax weather proofing tape...). Bend radius won’t be a problem as it’s The “ultra flex” Version of lmr400. The weight issue I will try to solve by fastening the coax to side of house tightly with cable ties below the conduit.

Will not impact performance.

I'd suggest a proper weather head at the top to keep crud out and make for a nice transition at the top.

UV rated (black) ty-wraps will work if you want to run it on the outside of the mast. They won't fall apart in the sun and will keep the cable from slapping around.
I like the weather head idea, hadn’t thought of that. I have to see if home crapo has something in stock tomorrow, as this is going up Wed morning (with scaffolding up side of house, to high for 35’ ladder and no other access).

I’ve used/tried to use “uv rated” wraps, with not much success. They do not last longer than a year on that side of my house. Direct sunlight for 6 hours in morning, Salt water, strong weather, cold, ice.... and they break. I try to use rubber coated stainless hose mounts made for the marine industry, that’s about the only thing that lasts here.
 

mmckenna

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I’ve used/tried to use “uv rated” wraps, with not much success. They do not last longer than a year on that side of my house. Direct sunlight for 6 hours in morning, Salt water, strong weather, cold, ice.... and they break. I try to use rubber coated stainless hose mounts made for the marine industry, that’s about the only thing that lasts here.
High quality name brand ones should work fine. I have several sites near the ocean and haven't had them fail.

You can also get stainless steel tywraps if you want to go hard core. I use those on tower installs and places where I know it's going to get beat. Haven't had one fail yet.
But don't use them on your aluminum mast.
 

Ubbe

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Professsional installations often use "cable socks" to hang vertical cables without damaging them. You put a sock around the coax at the very top of the pole and hang it on something, perhaps around the clamps for the discone. Mast poles pick up rain drops in it's whole lenght and it will be a substantial water dripping from it at the bottom. So lay some gravel or similar below it so it doesn't create a nasty mud pool.

Cable sock

/Ubbe
 

chief21

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Mast poles pick up rain drops in it's whole lenght and it will be a substantial water dripping from it at the bottom. So lay some gravel or similar below it so it doesn't create a nasty mud pool.
In addition, I'd suggest a drip loop in the coax at the bottom of the mast to keep that water from migrating along your coax to the building entry point.
 

WB9YBM

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thats why they make uv rated tie wraps that resist uv rays. also you can use scotch 33 electrical tape which holds up very well outside.
Yeah, but how UV-proof is the outside of the coax? I've heard one antenna engineer at Motorola tell me he considers coax expendable and in need of replacement every few years because of degradations caused by weather (haven't tested that for myself yet, though...)
 

mmckenna

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Yeah, but how UV-proof is the outside of the coax? I've heard one antenna engineer at Motorola tell me he considers coax expendable and in need of replacement every few years because of degradations caused by weather (haven't tested that for myself yet, though...)
Coax doesn't last forever. But I think "every few years" is a bit of Motorola sales talk. I have a few sites where cellular carriers lease space, they've had the same 1 5/8" Heliax for 20+ years now. Same with my 800MHz system, 26 years of 1 5/8" up there and no issues. Same with jumpers, etc.

I'm sure cheap Chinese coax will fail sooner. Improper installation/waterproofing, etc. will reduce life. It's a good idea to periodically sweep the lines looking for issues, but so far I've not had any issues with mine. That may have to do with better install practices than what most hobbyists are willing to follow.
 

RFI-EMI-GUY

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Coax doesn't last forever. But I think "every few years" is a bit of Motorola sales talk. I have a few sites where cellular carriers lease space, they've had the same 1 5/8" Heliax for 20+ years now. Same with my 800MHz system, 26 years of 1 5/8" up there and no issues. Same with jumpers, etc.

I'm sure cheap Chinese coax will fail sooner. Improper installation/waterproofing, etc. will reduce life. It's a good idea to periodically sweep the lines looking for issues, but so far I've not had any issues with mine. That may have to do with better install practices than what most hobbyists are willing to follow.
Heliax really could last forever even if the outer jacket flakes off. It is a corrugated copper tube with foam dielectric and more copper safely inside. The outer jacket is just mechanical protection.

I had an interesting discussion recently about cabling inside of a particle accelerator. Some dielectrics, especially Teflon will degrade from ionizing radiation.
 
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