IP Wireless Camera Query

that wrote: »

There are 4 pairs of wires in RJ45 connector, and ether net uses 2 pairs, so 4 wires left doing nothing (acting as a screen), and one pair is used for power

You also get POE splitter to split the signal and power, and you get POE injectors to put the power onto the cable. You have to get an injector that matches the cameras voltage. There are more than one standard POE voltage/spec

That's not correct.
Megabit Ethernet connections use 2 pairs, Gigabit/10 Gigabit use all 4 and you can still use PoE with Gigabit speeds.

Wires are not used as 'screen', they are used to carry data or power. You get a 'shield' with some types of CAT5/6 etc. cables (STP opposed to UTP cables) that have a tiny foil wrapped around the wires.

There are two main types of PoE: active and passive. Active: power is negotiated with the device. Passive: power is 'always there' (this is generally a non-standard, protocol).

Within the active type, there are also 2 major types: one uses the 2 unused pairs (if there are unused pairs), the other uses the same data wires to deliver current when there is no spare wire to be used.

Back to the original question, what OP would like to do can, in theory, be done, provided that the camera is a WiFi camera.

A normal PoE injector will give power to the camera without necessarily having to connect it to a network. Only make sure that the camera supports active PoE (802.3 standard). If it comes with its own proprietary injector you might not be able to use a generic one.

that wrote: »

thank you, things have moved on since my youth

I was taught, possibly wrongly, the second two pairs of cables had a harmonic screening effect, and stopped crosstalk. gut feeling you could get away with DC as it emitted no interference, but could not use the second pairs as another 10Mb connection

if the op is not careful, or lives in a congested area he could easily run out of bandwidth with wifi
https://www.supercircuits.com/resources/tools/network-ip-security-camera-system-bandwidth-calculator

The crosstalk problem was solved (or heavily reduced) by twisting the pairs, somehow the 'twist' gives protection (don't ask me why). Proper shielding (for example, if you run CAT cables alongside power cables) is achieved with shielded cables (STP cables).

CAT6 cables are even more protected, but they are a much more difficult to work with (less flexible, much harder to manually terminate).

In regard to WiFi, I agree, it's not the best option when it comes to cameras, especially if they are HD or greater. If you use the camera if and when required, WiFi is probably ok, but if it's a 24/7 monitoring system, you get congestion quite easily (provided that you get the minimum bandwidth anyway, given that it's an outdoor camera, good WiFi coverage could be a problem)

that wrote: »

Some pairs are twisted tighter than other pairs. not sure if any of the pairs are the same or if they are all different. Think the pairs are also gently twisted around each other. The idea was that the radiated signal phases would cancel each other out to a large extent... unless you put it alongside a florescent light

Yes that's right, and the weird thing (at least for me) is that, if you untwist all the wires in a 50-metre cable, for example, you end up having some wires longer than the others. I still don't understand how this works when you use the cable with serial connections, where data should be received 'sequentially'.