Flexible Coaxial cable?

[ggunn]

Is there any flexible coaxial cable which would be usable for ISP connectivity to a router or for a cable TV connection, or does the core conductor always have to be solid? I have tons of guitar cables lying around; could I just change the connectors and use one for CATV? I'm guessing not, but why would it not be able to handle the bandwidth? Capacitance, I'd guess, but what has a solid inner conductor to do with it?

 

[retirede]

Coax has an impedance rating for RF use. Most common is 52 ohm. Your guitar cable will have an impedance mismatch and likely incur higher than acceptable losses. It might work if the length isn’t too long.

 

[Birken Vogt]

Is there any flexible coaxial cable which would be usable for ISP connectivity to a router or for a cable TV connection, or does the core conductor always have to be solid? I have tons of guitar cables lying around; could I just change the connectors and use one for CATV? I'm guessing not, but why would it not be able to handle the bandwidth? Capacitance, I'd guess, but what has a solid inner conductor to do with it?

The center conductor does not necessarily have to be solid, but on CATV stuff it is generally copper coated steel because the center conductor itself is the terminal and needs to poke into the socket. If it was soft material or stranded it would just wad up.

The type of connector is referred to as an "F" connector. The cable is 75 ohms, not 50 ohms like most other radio stuff.

Maybe somebody is selling a flexible or stranded cable with some sort of F connector pin crimped or soldered on the end, in fact I can almost guarantee it has been made at some point in history, but it will not be common or easy to find.

 

[ggunn]

The center conductor does not necessarily have to be solid, but on CATV stuff it is generally copper coated steel because the center conductor itself is the terminal and needs to poke into the socket. If it was soft material or stranded it would just wad up.

The type of connector is referred to as an "F" connector. The cable is 75 ohms, not 50 ohms like most other radio stuff.

Maybe somebody is selling a flexible or stranded cable with some sort of F connector pin crimped or soldered on the end, in fact I can almost guarantee it has been made at some point in history, but it will not be common or easy to find.

Thanks, but that brings up something else I do not understand; when it's said that a cable is 50ohm or 75ohm, what does that mean? Resistance of what, measured how?

 

[OldBroadcastTech]

" a cable is 50ohm or 75ohm, what does that mean?"

that refers to its 'CHARACTERISTIC IMPEDANCE'

which depends upon:

inner conductor outer diameter
thickness of insulation
dielectric constant of the insulation
outer conductor inner diameter

more here:

Coaxial Cable Impedance Calculator

Fairview Microwave's Coaxial Cable Impedance Calculator allows you to enter the Outer Diameter Dielectric width, Inner conductor Diameter width and either the Dielectric Constant or Velocity of Propagation (VoP) values in order to calculate the impedance of the coax.

www.fairviewmicrowave.com

Hope this helps

 

[ggunn]

So apparently it is impedance (RLC) per some unit length. Obviously, absolute resistance, capacitance, and inductance are going to vary with cable length.

 

[zbang]

Impedance is not length-dependent. What you need is a smaller diameter 75 ohm cable with a softer jacket which will then be more flexible. You can usually get something that will work at and electronics or hardware store.

 

[LarryFine]

If you just need a short piece, look for a flexible coax wall-to-TV jumper cable.

 

[ggunn]

Impedance is not length-dependent.

Can you 'splain that? I can see that characteristic impedance is length independent but I do not see how absolute impedance cannot be dependent on cable length. Maybe changes in capacitance and inductance cancel (?), but resistance is length dependent.

 

[VirutalElectrician]

Coax cable is almost free on FBMP.

 

[ggunn]

Maybe changes in capacitance and inductance cancel (?), but resistance is length dependent.

Scratch that; both capacitance and inductance increase with increasing length of a cable.

 

[Speedskater]

The 50 & 75 Ohms, refers to the Radio Frequency Characteristic Impedance. It starts to kick in somewhere above 100 kilohertz.
It's the ratio of capacitance to inductance.
At power line and audio frequencies the formula is way more complicated.
At radio frequencies cables act as transmission lines.
In well behaved transmission lines, the output stage impedance, the cable impedance and the input stage are all the same. The cable can be any length from zero to infinity.
* * * * * * * *
At high radio frequencies, because of skin-effect all the signal travels very near the surface of a conductor. So stranded wires are good only at lower frequencies.