EXCESSIVE COAX

[Swamp Yankee]

Hello All,
What should I do with my excessive coax for a Base Station? Can I just roll it up (not tightly) and tuck it away behind my bench? Should it be cut as short as possible? Thank You.

 

[BC Coyote]

If you have a huge amount of excess (like 50 feet or more) I would cut it. If it's less than that just coil it up somewhere handy and out of the way. The amount of loss in less than 50 feet of coax is minimal at CB frequencies..........

 

[Shadetree Mechanic]

I have a "temporary" setup in the back of the house with my work bench. I ran coax from my radio room to it so I can play with radios on the bench. The coax is 50 feet and only goes about 25 feet between rooms. I didn't want to cut it so I just looped the extra 25 feet in a 2 foot diameter loop, and hung it on the wall. Hasn't been a problem as far as I can tell. Your milage may vary.

 

[Swamp Yankee]

Thank You. The length is around 20 feet. I'll just tuck it away...

 

[unit_399]

NEVER coil up excess coax !! Coiled up, It will act as an Inductor and cause multiple problems. String it out along the floor and run it back and forth, but never let it cross itself,
The best solution is to shorten it, but if you'd rather not do that, just make certain that it doesn't cross over itself.

_- 399

 

[BC Coyote]

It will act as an Inductor and cause multiple problems

No it doesn't. It actually acts like a choke or loose balun and can help with common mode currents, especially with antennas such as the A-99 that operate without a conventional radial system.
I've had about 30 feet of extra RG-8 cable coiled up on the ground under my shop for years and years.......never had a problem. My match is excellent and I have almost zero RF in the shack.

 

[Captain Kilowatt]

NEVER coil up excess coax !! Coiled up, It will act as an Inductor and cause multiple problems. String it out along the floor and run it back and forth, but never let it cross itself,
The best solution is to shorten it, but if you'd rather not do that, just make certain that it doesn't cross over itself.

_- 399

Wrong. The turns are shielded from each other and it does not act like an inductor. Only the outer shield is not shielded from each turn next too it and it will form an inductor aka choke to prevent common mode currents on the OUTSIDE of the cable. It has ZERO affect to the inner conductor.

 

[sp5it]

Use that excessive coax to make choke baluns. One right under antenna feedpoint, another where coax enters house.
Mike

 

[Enterprise312ok]

I have observed mobile setups where coax coiled around mirror arms in stead of using zip ties to secure has caused swr issues,.

 

[BC Coyote]

I have observed mobile setups where coax coiled around mirror arms in stead of using zip ties to secure has caused swr issues,.

If everything is perfect with the antenna (which it usually isn't in a compromise mobile situation), then you should be able to do pretty much anything with the coax and not have it affect SWR. If SWR is being changed by moving or coiling cable it means the antenna itself isn't working to full efficiency and the cable is acting as part of the ground plane.

 

[Captain Kilowatt]

I have observed mobile setups where coax coiled around mirror arms in stead of using zip ties to secure has caused swr issues,.

That would be due to common mode problems where a less than ideal ground plane is present and RF is flowing on the OUTSIDE of the cable where it is not supposed to be.

 

[M0GVZ]

NEVER coil up excess coax !! Coiled up, It will act as an Inductor and cause multiple problems. String it out along the floor and run it back and forth, but never let it cross itself,
The best solution is to shorten it, but if you'd rather not do that, just make certain that it doesn't cross over itself.

_- 399

Sorry but this is rubbish. Absolute unadulterated bollocks.

It won't cause any problems unless you have a poor RF ground and no choking at the antenna so the coax is being used to compensate making it part of the antenna. As long as your antenna installation is done properly other than bending it tighter than the minimum turn radius in the specs it shouldn't make any difference what you do to it. If it does then this is indicating you've a poor RF ground, the coax is forming part of the antenna which is bad and you're most likely also suffering common mode RFI too.

 

[M0GVZ]

I have observed mobile setups where coax coiled around mirror arms in stead of using zip ties to secure has caused swr issues,.

Yes. That's because they've got a poor RF ground so the antenna system is trying to use the coax to compensate for that. By coiling it up they're choking off the coax after that coil, effectively altering the length of the antenna as far as the antenna system sees it, which alters the tuning.

 

[unit_399]

Wrong. The turns are shielded from each other and it does not act like an inductor. Only the outer shield is not shielded from each turn next too it and it will form an inductor aka choke to prevent common mode currents on the OUTSIDE of the cable. It has ZERO affect to the inner conductor.

Sorry but this is rubbish. Absolute unadulterated bollocks.

It won't cause any problems unless you have a poor RF ground and no choking at the antenna so the coax is being used to compensate making it part of the antenna. As long as your antenna installation is done properly other than bending it tighter than the minimum turn radius in the specs it shouldn't make any difference what you do to it. If it does then this is indicating you've a poor RF ground, the coax is forming part of the antenna which is bad and you're most likely also suffering common mode RFI too.

Captain -
Thank you for making my point. I never mentioned that the inner core would be an inductor, I just said that it will form an inductor, which the shield will do. If common mode currents are present on the coax, choking them off inside the shack is not a good idea as I see it. Instead of taking chances of it causing problems, just don't coil it up in the first place.

MOGVZ -You call my post "rubbish,", and then say,"It won't cause any problems unless . . ." Nice tap dancing.

- 399

 

[Shadetree Mechanic]

I just stumbled across this.....

Coiling the coax cable causing problems....a myth or fact?

I gotta ask this one...I've heard that you're not supposed to coil up the coax cable from the antenna to the radio. I forgot why but it had something to do with how the radio performs. I believe I've also read this is bunk. In my situation I am installing a dual band ham rig in my truck...

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