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question about my new coax

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byron81ward

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Jan 6, 2013
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i just purchased 100 feet of lmr400 coax gonna put it up saturday weather permiting putting it on my i 10-k i have a friend who told me i chould loop it 4 or five times in small loops and zip tie them where it goes into the feed of my ann
tenna has anyone else heard this and does it help or is it b.s. thanks 181 the bulldozer s.il.
 

Might help prevent common-mode current from flowing on the outside of the shield; therefore it might help with RFI.

However, with LMR-400, you don't want to coil it in "small loops". First, it's pretty inflexible, what with having a solid center conductor. Easier would be to take either RG-213 or LMR-400xf (extra flexible) and form it into coils no less than 8 inches in diameter. Don't use zip ties; they tend to crush the cable, forcing the shield closer to the center conductor. Use UV-resistant tape.

You can use a "barrel connector" to connect the stiff LMR-400 to the flexible coax. Be sure to weather-seal all the connectors.
 
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yes, its called a choke. about 8 wraps near the antenna will make sure the outer shielding does not pick up RF from the antenna and feed it back into the shack, the choke creates a electromagnetic field that dissipates the stray RF. depending on antenna design, swr, etc it is not absolutely necessary but can do no harm, especially as you TX further off center freq you tuned the antenna for.

good article
RF Choke Coil - K3DAV - Amateur Radio Operator
 
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Do you live in a residential neighborhood with close neighbors? If not, don't worry about it. Now, if your family gripes about RFI affecting their electronics, then you may want to consider it.
 
thanks for the feedback i live in the boondocks man my friend also said it would help in case of lightning strike i think i will try it thanks again
 
i read that article towerdog posted thanks. yep if lightning strikes its all over lol. but im gona try it for the rf looks like a good idea
 
byron81ward said:
thanks for the feedback i live in the boondocks man my friend also said it would help in case of lightning strike i think i will try it thanks again
Click to expand...

Would be naive to consider that the choke will do anything to protect your equipment or your house from the damaging effects that can be caused by a lightning strike to the antenna.
And it would also give a false sense of security which might prevent you from exercising really effective methods of lightning damage protection.
 
Robb posted a very nice chart on a recent thread titled ''ugly balun deja vu", which provides the number of turns needed to build a choke, by frequency and type of cable.
 
byron81ward said:
i just purchased 100 feet of lmr400 coax gonna put it up saturday weather permiting putting it on my i 10-k i have a friend who told me i chould loop it 4 or five times in small loops and zip tie them where it goes into the feed of my ann
tenna has anyone else heard this and does it help or is it b.s. thanks 181 the bulldozer s.il.
Click to expand...

I can't speak for LMR400, as I run RG8X (which is far more flexible). What I can tell you is that I'm not splattering on either myself or my neighbors (believe me, I've tried, and I've asked). I have an RF Choke directly below my feed-line (5 turns @ 4 1/4 inches diameter) and I've been doing just fine for years on 11 meters.

Here's a picture of my RF Choke. I actually wrapped it around my washing machine's agitator (which just happens to be 4 1/4 inches in diameter, lol -- no, I'm serious).

RFChoke.jpg
 
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whatever you do,..... I would highly recommend that you NEVER let your "friend" use his golden screwdriver" on your equipment;)
 
Ive always put large loops in my feedlines (coax) befor it enters the house. Reason being is lightning as we all know has massive force and likes fastest path to ground and doesnt like sharp bends and corners so its always been said that a few coils may help due to the lightning blowing through the coax loop to ground.

Theres no gurantee but I was told this years ago by a antenna tower company so Ive always done this. I also disconnect all feedlines from the house if weather shows storms coming.
 

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