• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

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

Turbo T

Certified CB Rambo
Feb 2, 2011
963
141
53
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 and using a mag mount antenna that comes with like 17 ft. of coax. I did coil the coax under my seat.

Can anyone let me know for a fact if this is ok or not?

Thanks in advance.
 

From Firestick.com
http://www.firestik.com/Tech_Docs/63Things.htm

21. Excess coax between your radio and antenna mount should never be wound into a circular coil of less than 12" in diameter. Doing so can cause system problems. Your best option for handling excess coax is to serpentine the cable into a 12 to 18 inch yarn-like skein. Secure the skein in the center with a wire tie and tuck it away.

This guy talks about eliminating comman mode current by using a choke (coiled up section of coax) at the antenna.
http://signalengineering.com/ultimate/coax_basics.html
scroll down a little. Look for this {Why does my coax length affect the SWR of my antenna?}
 
Last edited:
So what are you supposed to do with all that coax?

It's a mag mount antenna so I don't want to just go cutting it.

There's still a bunch of coax in the cab of my reg cab S-10.
 
There can be a problem when coiling up coax, but it's a mechanical problem. As in winding it too tightly and causing distortion. If the dimensions on the inside of that cable change, so does the impedance of that cable. If that distortion is severe enough, the center conductor will 'migrate' to the side and eventually short to the braid. Neither of those two things are something that's 'good' for your radio.
How tightly you can coil coax cable depends on the cable. There are several different 'sizes' of coax, some are 'stiffer' than others. That 12 inch coil thingy is only a rough 'average' size of the coiled up cable, that can certainly be too tight for some cables, and very 'loose' for others. For the usual type of coax that people normally use, it's a fairly nice average size of coil. If you really have to force a cable into a particular sized coil, then it's probably too tight.
With coaxial cable, the inside is very different from the outside, electrically. Like a pipe. You can run a pipe of pure water through really nasty water and the stuff inside that pipe stays pure, right? Same thing with electrical signals and coax cable. Also like a pipe, things can travel on the outside of it and get into what that pipe carries and contaminate it where there's an 'opening', or at the ends of the pipe. The 'trick' is to not furnish the electrical thingys on the outside of that coax an opening to get into what that coax is carrying, keep it 'sealed'. Sealing things electrically is very different than sealing things mechanically.
RF signals are alternating current, AC, not direct current, DC. So there are some electrical characteristics that play a part in that "keeping the insides of that pipe" clean. Inductance, coils, are one way of doing that. A coil, or inductance, impedes, or slows, or stops, AC. So, if you wind a coax cable into a coil you produce some inductance on the "OUTSIDE" of that coax. That inductance slows or stops electrical signals from flowing on the 'outside' of that cable. Which is good, and the whole idea of an RF 'choke'! It chokes off that stuff on the outside of the cable. It has no affect on what's inside that cable unless that coil distorts the cable which changes it's impedance which means you wound the @#$ thing too tight (you can bend a pipe too much and it splits, right?).
That's a very 'rough' explanation, not very scientific or exact, so take it as such. To complicate things jsut a bit, the outside of coax cable can be used to conduct things/signals that you do not want to mix with what's inside that cable and you have to keep those two kinds of signals separated. It's done quite often. The 'trick' with that is to keep them separated by using other electrical characteristics. :)
- 'Doc
 
Your best option for handling excess coax is to serpentine the cable into a 12 to 18 inch yarn-like skein. Secure the skein in the center with a wire tie and tuck it away. AS kor b suggested.
 
Thanks...but it sounds as if you're basically telling me to take the excess coax and wind it around something that's at least 12-18 inches big? Like a spool?

(I don't know anything on skeining yarn - sorry)
 
So what are you supposed to do with all that coax?

It's a mag mount antenna so I don't want to just go cutting it.

There's still a bunch of coax in the cab of my reg cab S-10.


As many times as this is asked it just never seems to go away.

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 and using a mag mount antenna that comes with like 17 ft. of coax. I did coil the coax under my seat.

Can anyone let me know for a fact if this is ok or not?

Thanks in advance.

Coiling up the coax will not hurt a thing as long as the coax cable is not wound in too tight a coil so as to cause physical damage to the cable.

Coiled wire is a choke. You add inductance, not very good for SWRs.

No you do not add inductance. The coax cable shield isolates each turn from the next one.The only inductance created is on the shield itself and that only comes into play if common mode currents are present on the shield. Again, coiling coax does NOT add inductance and will NOT affect SWR. Been doing it for almost 35 years on frequencies from 1.8 MHz up to 1.7 GHz and haven't seen it happen yet.The coiling adds inductance myth is due to a misunderstanding of what common mode currents are and how they can be choked off using a coil of coax at the antenna feedpoint. The inductance is only present on the shield and NOT on the inner conductor.
 
Coil it up like you would a rope. Nothing particularly special about how it's done, maybe neatness?
- 'Doc
 
Thanx kor b that does help, only thing is I don't have anything to wrap the coax around other than maybe the bench seat.

I suppose I could freely run the coax around the underside of the seat?
 
Thanx kor b that does help, only thing is I don't have anything to wrap the coax around other than maybe the bench seat.

I suppose I could freely run the coax around the underside of the seat?

you don't have to physically wrap the coax around anything, just make sure the loop is around 12"+ in diameter :)
take connector in hand and make 12" circle...got some left? make another circle and so on until you've used up all the extra coax....free up enuf to make connection to radio, lay extra anywhere it's not gonna see a lot of traffic (like under seat) and you're good..
 
Thanx kor b that does help, only thing is I don't have anything to wrap the coax around other than maybe the bench seat.

I suppose I could freely run the coax around the underside of the seat?

you don't have to physically wrap the coax around anything, just make sure the loop is around 12"+ in diameter :)
take connector in hand and make 12" circle...got some left? make another circle and so on until you've used up all the extra coax....free up enuf to make connection to radio, lay extra anywhere it's not gonna see a lot of traffic (like under seat) and you're good..

:headbang Man, since when did coiling up something require directions? :whistle:
 
  • Like
Reactions: 1 person

dxChat
Help Users
  • No one is chatting at the moment.
  • dxBot:
    Tucker442 has left the room.
  • @ BJ radionut:
    LIVE 10:00 AM EST :cool:
  • @ Charles Edwards:
    I'm looking for factory settings 1 through 59 for a AT 5555 n2 or AT500 M2 I only wrote down half the values feel like a idiot I need help will be appreciated