It's not a TV antenna wire... what IS it?

Central_ValleyDecember 7, 2012

There's a wire hanging down from the ceiling in one of my house's closets. I always thought it was an old style TV antenna wire: the kind with two parallel conductors separated by a web of plastic.

Last night I actually needed the thing, and took a close look for the first time. It's something I've never seen before, and I don't know what.

Imagine an old style TV antenna wire that's about twice as wide as normal, with four conductors instead of two. One of the outside conductors is silver colored; the other three are copper. All are much heavier than one would expect, probably about 14 gauge.

The house has a wall-mounted antenna rotation control. The wire might be related to that... but if so, why is it in a closet about 20 feet away from the control?

A stereo speaker cable? If so, why four conductors in ONE cable? The two pairs have to split at some point, so why bind them together at all? And why one silver conductor, three copper?

And if the wire is meant to be attached to any kind of electronic device, why put in a closet in the front hall, where any device placed outside the closet would tend to block the door?

Any ideas?

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tjdabomb

Any pictures??? They really do say a thousand words.

    Bookmark   December 7, 2012 at 12:15AM
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alan_s_thefirst

I do seem to remember the antenna rotators used 4 wires.

The wire in a closet might just be how it was routed.

As for 3 copper, one silver, it's probably tinned/plated copper. I would guess that's a common ground or negative, and the other three are the + feeds.

If it was speaker wire, the advantage of combining them is you only have to run one wire, and split it or splice it when you separate out the channels.

    Bookmark   December 7, 2012 at 1:29AM
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Ron Natalie

I agree with ALAN. Four or five flat wires is probably an atenna rotator. They used to key it by coloring a condutor on one side silver.

    Bookmark   December 7, 2012 at 8:23AM
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brickeyee

Some of the rotor lines could double for RF signals.

    Bookmark   December 8, 2012 at 1:01PM
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yosemitebill

"Some of the rotor lines could double for RF signals."

Say what?!! I have never, ever heard of this or seen it done. And most certainly could not be done for amateur radio.

Rotors since the 60's have typically used 30VAC with two windings and a common from the box to the motor.

The rotor wiring used the silver wire (or the one with the wider insulation) as the indicator for #1 on the terminal strip on the box and at the rotor - the copper wires just followed along in sequence. When interfacing 3&4 wire systems later on, you just simply combined wires 3&4 at whichever end.

    Bookmark   December 8, 2012 at 8:18PM
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brickeyee

"Some of the rotor lines could double for RF signals."

"Say what?!! I have never, ever heard of this or seen it done. And most certainly could not be done for amateur radio.

Rotors since the 60's have typically used 30VAC with two windings and a common from the box to the motor. "

The presence of 60 Hz or other power signals (down to DC) on the line has no effect on their use as RF lines.

Al you need is a simple network to separate signals at the load end.

It is very easy to pull off even kHz RF from 50 Hz ad direct each signal to their respective loads.

The bigger problem for RF use is what impedance you have created with the structure of the pairs.

For rotor control lines a small value inductor stops the TRF from passing into the rotor controls and motor.

A capacitor allows the much higher RF frequency to be coupled on the lines and then coupled off.

The bigger problem for RF use is making sure the cable has suitable impedance at RF to allow things to work out correctly.
Typical 'twin lead' is 300 ohms, while 600 ohm twin lead is not unheard of.
If you had more money you could use coax for the RF line.

the required coupling networks are much cheaper than running an extra cable run (especially if home built).

this is the same method used for microphones for many years before wireless was high enough quality.

A 'phantom DC voltage' was put on the audio lines to power the microphone electronics, and ten easily blocked from the output at the amplifier.

All sorts of signals can share conductors.

DSL is placed on the twisted pair phone line above the normal audio.

This post was edited by brickeyee on Sun, Dec 9, 12 at 12:02

    Bookmark   December 9, 2012 at 11:00AM
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bus_driver

The antenna rotors with which I am familiar are the Alliance which used a cable as described above. I suspect that Alliance is now out of that business. The cable was for the rotor only with separate cable for the RF signal. Genie made a rotor, but I have no experience with that brand. Channel Master uses just 3 conductors. Channel Master also makes several other house and private brands, including the Archer for Radio Shack.

    Bookmark   December 9, 2012 at 1:30PM
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yosemitebill

Brickeyee, you are confusing sending AC or DC voltages up a high impedance, high frequency signal cable - with attempting to send high impedance, high frequency signals down a low impedance AC or DC cable.

What do you think is going to happen to the RF antenna signals hitting the winding of the 60Hz AC rotor motor? This is one of the biggest problems faced by utility companies attempting to use PLC (power line communications).

Phantom power has been used for years, such as 30-90VAC for CATV trunk-line amplifiers, to 12/18VDC used for satellite LNBs and residential antenna amplifiers. 48VDC phantom power is still very commonly used for music studio condenser microphones and has nothing to do with the advent of wireless technology.

There is currently one company, Eagle Aspen, that makes a light-duty antenna rotor that sends 18VDC power and control signals based upon DiSEqC (really spelled that way!) up the coax, but this is the inverse of what you are suggesting.

    Bookmark   December 9, 2012 at 8:21PM
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