Effects of coiling cable.

[flyingwolf]

I picked up an old base station antenna today.
The elements are shot but I plan to use it and its original base to make another antenna out of.

It has about 12 to 15 foot of cable from the mount to the connector.

I would prefer not to cut the wire in case I want to move it.

So rather then just throwing the cable on the floor in untidy heaps I would like to coil it and wire tie it.

What are the benefits (if any) and drawbacks (if any) of coiling the cable up and only using the length I need.

 

[Thayne]

If it is coax that is coiled loosely is should not make any difference; just don't kink it or anything.

 

[MarkWestin]

Coax Cable

Hello,

As Thayne said "If it is coax that is coiled loosely is should not make any difference".
I will add the length that you have is quite short. If you had 50 feet or more you might have a problem. I have seen problems with cutting coax cables, and they were not what you might expect. If the length of the cable is exactly the wrong length, You might not be able to receive anything because its length could match a certain wavelength. I was a Radar Tech in the Navy and in the Radar unit they use a Diplexer made from Waveguide. By putting a 1/4 wave shorted stub at a certain length (wavelength) from the receiver, the designer could have a bandpass or bandstop filter with no other parts except for what looked like a little box attached to the bottom of the Waveguide. Coax Cable works more or less like a Waveguide. Sometimes it is better to not cut a cable so that it is nice and neat. If you have to coil it up, that is ok but it is better to sort of hide the cable and run a long loop instead of coiling it up.

Mark

 

[Al42]

If the length of the cable is exactly the wrong length, You might not be able to receive anything because its length could match a certain wavelength.

That's if the antenna and cable aren't the same impedence. If they are you can use any random length of cable.

A coil is an inductance, which tends to attenuate signals. How much it attenuates depends on the frequency, the diameter of the coil and the number of turns. But more than 2 turns at 850 MHz isn't a good idea, even if the coil is a foot in diameter..

 

[kb5udf]

Signal attenuation?

That's if the antenna and cable aren't the same impedence. If they are you can use any random length of cable.

A coil is an inductance, which tends to attenuate signals. How much it attenuates depends on the frequency, the diameter of the coil and the number of turns. But more than 2 turns at 850 MHz isn't a good idea, even if the coil is a foot in diameter..

I thought coiling coax only attenuated RF on the braid/shield, not the conductor?

 

[N_Jay]

I thought coiling coax only attenuated RF on the braid/shield, not the conductor?

Don't confuse him with the facts. (J/K)

 

[Al42]

I thought coiling coax only attenuated RF on the braid/shield, not the conductor?

Coiling a wire forms an inductance - any wire. You're thinking of making a pseudo-balun by coiling coax so you don't get radiation from the shield when feeding a balanced antenna.

 

[Thayne]

Does that mean a rattlesnake is a pseudo-balun?

 

[bsavery]

That's why they coil up.... so their fangs don't pick up radio stations! :lol:

Bob

 

[N_Jay]

Coiling a wire forms an inductance - any wire. You're thinking of making a pseudo-balun by coiling coax so you don't get radiation from the shield when feeding a balanced antenna.

Coiling a wire does create a inductor.

HOWEVER; the current flowing INSIDE the coaxial cable are unaffected by the inductance outside the cable.

Only currents flowing on the outside of the shield (caused by impedance mismatches) will see this inductance.

Since most scanner antennas are poorly match you may see soem signal difference, but it could be an improvement or decrease in signal level and may ilso decrease interference.

 

[unitcharlie]

So if I climb on the roof and uncoil the RG6 I should receive 800 meg better?

 

[N_Jay]

So if I climb on the roof and uncoil the RG6 I should receive 800 meg better?

How much RG-67.

The answer is;

Maybe, Maybe not!

And that is as definitive as anyone can get.

(Unless they want to start making stuff up)