# Sending a signal with one strand of wire.

Am I right in assuming that a signal can be transmitted from A to B with a single strand of copper wire? There doesn’t need to be a return wire to complete a circuit, right? What are the limits of one strand of wire?

Coax sends a tv signal from god knows where to my TV using just one single copper wire, right? But to send a large amount of power, I’d have to have a complete circuit, right? It’s obvious I am missing some key knowledge.

you need to clarify. If by signal you mean information then you are correct. One could tug on one end of the wire and send a signal to the other end. If you mean an electrical voltage, then you always have to have another point to measure across. Usually it is a ground or neutral wire, sometimes it is the ground itself. Coax, BTW, has two conductors in it: the central wire and the grounded sheath. It won’t work correctly unless both are properly connected.

Correct - an “earth return” scheme is sometimes used to complete the circuit (but this is not common).

As rbroome notes, Coaxial cable has two conductors: an inner core and an outer shield.

This is all general and specific circumstances are exceptions. A one wire electric connection uses ground to complete the circuit. The ground is not as good of a conductor as copper. Ground isolated devices can transmit via one wire, but you have to think of the communication like a charging discharging capacitor. You will have to allow an equal reverse flow of the electrons via the same wire at some point to have a signal. With a two wire system you can transmit out on one wire as on and another as off. Power does not have to oscillate (push and pull) via one wire.

I’m really have problems trying to come across clearly lately so if this helps that’s great, if not sorry it’s confusing.

I mean say I have some device sitting 500m away. It could be a laptop computer, a iPod, a radio… something self powered. Could I rig it so that I could push a button 500m away and tell it to turn on, using only a single strand of wire?

The the button which sends the signal across the single strand of wire could be a device of any complexity, but let’s say it is limited to a 9-12volt power source. Tell me… how simple can it be made?

Would it involve a ground spike at both ends? Would a low voltage signal work through a ground return system???

This hypothetical system doesn’t need to communicate both directions. Only an ON signal needs to be sent from a control device, to the receiving device.
Let’s assume, also, that it’s a one time use thing.

You could do it with a FET. What you do is, you apply a voltage to the wire–that’s your signal. FETs are voltage-operated transistors (FET stands for field-effect transistor, as in “electric field”), so if you connect the wire the gate terminal of your FET, you can apply a voltage at the other end and turn the FET on. The main problem with this is due to the necessarily high impedance of the FET, any little stray voltage, such as a static charge from your cat walking by, will be enough to trigger the FET. You can get around this by sending a modulated signal instead of a simple voltage-on/voltage-off which, of course, requires some sort of discriminator circuitry on the FET output; but now you’re entering a level of complexity where simply using two wires is both cheaper and simpler.

Two wires are going to be vastly more reliable than one. Why the desire to use one wire?

You are still referencing to ground.
If the laptop was floating in a vacuum, this wouldn’t work.

Obviously, I realize that. But, you don’t specifically have to supply a ground connection, which was the point here.

The OP seems like a theoretical question. So the answer is “no”.

So then, within the parameters and the voltage limits, it would be a simple set up? The control device would only have to be attached for like 5-10 minutes before sending an ON signal–so that could probably limit the chance of a cat or something setting it off, I guess.

Also, would the fact that the copper wire is bare, unshielded, uncovered, and uninsulated change any of the answers? Is this physically possible with just a single strand of bare copper wire exposed to the elements?

Wait… the answer is “No” now? You are saying it cannot be done?

What are you trying to do? Answering that would help a lot.
Why not just use RF or IR to control this wirelessly?

There’s not enough specifics available to say “yes” or “no” with absolute confidence.

You do need a complete circuit, period amen. In theory, a simple ground stake at each end ought to be a good enough to provide the return path, and a single strand of even 22ga uninsulated copper ought to be enough to carry some current.

Now comes the details: how much voltage are you pushing in? What is the current draw of the thing you’re controlling? How much current is available to push that voltage? What is the wire guage for your single strand? If it’s mechanically supported along the run, what is the leakage of the insulator(s)? What is your ground stake material? How long/deep are they? What is the soil composition? Soil moisture?

etc., for another fifty questions. Then somebody can compute the answer.

Ballpark, I say a 12V car battery can push enough current through 20ga wire over 500m to engage a small relay, provided the earth ground path is high quality, which imples high soil moisture as well as good physical bonding between the wiring, the ground stake, and the soil. A 10p nail driven into loose sand in a desert probably won’t cut it. A 3’ copper rod driven into mud might.

I was under the impression that it was possible to send a signal via a single conductor without reference to a common ground, by treating the device at the other end of the wire as one side of a capacitor.

I found this system, which uses a single strand to communicate either on or off positions.

:rolleyes: Yes, I’m sure he’s using his laptop in deep space.

I’m not trying to do anything. I would rather have kept it vague, but I guess it’s impossible to get a perfect answer with an imperfect question.

I’m talking about command wires for IEDs. I understand how IR, RF, command wire (with two wires), fuse, pressure plate, crush wire and pretty much every kind of initiator works.
However, I have come across thread-thick, uninsulated copper wire strung across great distances. Others have claimed with no doubt that it’s a command wire. I have seen these wires terminate at what seem to be obvious observation points. So, the likely are some type of command wire.

But I can’t comprehend how exactly a single strand of copper wire can do anything WRT sending a current or electric signal from A to B. I doubt that the 3’ stake in the ground is the method. Is it possible to use such a medium to trigger a device?

Please keep your posts here as vague as possible for obvious reasons. If you have expert knowledge and lots of details, I’d appreciate a PM from you.

Bottom line, could something be used as a primitive command wire or not?

Could you elaborate?