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Telephone line ringing in Canadian cities is with 90V RMS 20Hz riding on the telco's -51V battery. The cadence is two seconds of ringing followed by 4 seconds of silence.
I don't remember how little current is allowed because the feds call it "ringer equivalence number" instead of the actual current to confuse everyone. I think you are allowed a max of 5 old-fashioned mechanical ringers on a phone line.
If your homemade gadget exceeds the max current then the feds will come to chop off your head. :lol:
Unless things have changed in recent years?, you're not allowed to connect any unapproved apparatus to the UK phone system - which means you can't connect anything home made (unless you want to pay many thousands to get approval?).
Im not sure how they go about the business of detection. Drawing the same, if not less, on hook current as a standard telephone should be very difficult to detect.
In the old phones, when on-hook only connected the ringer coil (1kohm) serial with 1uF capacitor to line. This mean about 8-10mA ring-current. In my country not possible connecting over 4 old phones. When problems occurs, in the phone-centrale easy to measure the number of ringer (phone).
Maybe the Telco is smart and when they detect too much ringer current then they can send a high-power blast down that line to blow-up the home-made stuff. They do it anyway to get rid of ice on the line.
That's what we did when someone put his own 8 ohm speaker on a 70V PA system. His speaker overloaded the PA amp and was hard to find, so we connected the line to 120VAC for a second to blow-up his extra speaker. The whole building hummed for a second and in one location there was a BANG! Lotsa fun. :lol:
Maybe the Telco is smart and when they detect too much ringer current then they can send a high-power blast down that line to blow-up the home-made stuff. They do it anyway to get rid of ice on the line.
In my experience, as Nigel said, they don't actively search for problems. Mostly the problems "report themselves." As in the customer with faulty equipment will call the phone company to report a non-working line. When the phone comapany checks the line and finds you are the source of the problem, well, the problem is solved.
When I worked for a cable TV company, on slow days we would root out suspected illegal taps. On the cable system there was a FM signal added that had a warbling tone. While driving around in a service truck on routine maintenance, an ordinary FM reciever was set to the right frequency, and if you heard the tone, you knew either someone was using twin-lead/crappy coax to an extra TV or a faulty cable drop was radiating. Knocking on doors would often cause the signal to "magically" stop as people disconnected the illegal taps. We would say we were trying to fix a problem in the area, and wondered if everything was OK with their cable service. 8)
We used to run two old small cable systems, all valve equipment, and all thrown out once local relay transmitters appeared :lol:
They used line level cables and resistive tap-off boxes, both were all VHF, and only one included UHF channels, down converted to VHF.
One day we got loads of reports that one of them was down, it turned out some guy had connected himself directly to the main line, shorting it out for everyone else down stream.
We disconnected him, reconnected him properly (and got him to sign a contract!) - but he had to pay to have his TV repaired as well, the front end valves needed replacing to make it work. Presumably due to the high signal levels?.
We were so pleased when we ripped it all out :lol: it was such a pain!.
I dont think telecom tests stuff anymore. I've recently found caller display units, supplied by telecom, that fail to comply with their specifications regarding line loading and wetting pulses. Consequently I've built stuff that also doesnt comply, saving a good handful of components and a lot of PIC code. No trouble at all with it, and I've even left the stuff on while telecom engineers looked for a line fault.
I think a "wet pulse" is a fairly high voltage, high current pulse sent down a telephone line to burn the oxide off relay contacts. A dry circuit has very little or no current like from a dynamic microphone (coil and magnet) and needs a relay with gold-plated contacts.
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