ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades OT: Wired radio connectors

in our school it was a 2-way intercom thing and I think you could make announcements specific to various zones or "page all".

The 2-way facility was apparently abandoned after lots of students kept pressing it and the principal had no idea where the calls were coming from

Sven,
As far as I can tell, the system was a one-way 100V system, using a matching transformer and volume control at each speaker.
The volume control wasn't a standard potentiometer, but it was a 6-position switch connected to various resistors.
Now that I come to think of it, in the position with the least resistance, you'd only need a speaker in every second room, because Man was it LOUD!!.
These days if there was something that loud in a classroom, the kiddies would all have to wear OSH-approved ear protection, National Anthem or not!.

My schools had two way inter coms. I think each classroom speaker had a cable set going to the office, and an annuciator device to show which classroom called. The older section of the school had speakers above the blackboard, anfd the switch below or beside it. Newer sections of the school (built after the mid 1960s) hade a speaker box with a switch on it. The vocational shops had a telephone like hand set and a cradle with a switch, and a horn PA speaker.

* if things are right, your toaster could emit music causd by thaudio signal going through the heating element.

** FM on cable. Done in North America too, at least until the mid 1990s. You could often hook cable up to your regualr stero system receiver. Many had a 75 ohm or 300 ohm input.

I remember having a wired system in my old Junior (Elementary) school in the 1970s, which I would say was probably installed when the school was built in the 1950s.

I have no idea what system was employed, but I would guess it was the standard 100V PA line. My memories are somewhat vague now, but I know for certain they piped BBC Radio 4 VHF/FM around the school (as that was used for school broadcasts at the time). As for PA announcements originating from the principal's office, I can't say I ever remember any, but the feature probably existed.



Not directly related to cable radio, but the following link has a good article explaining the development of cable TV systems in the United States:

http://www.sbe24.org/archive/c24sep97.asp

(Scroll down about halfway to the section titled "BROADBAND NETWORKS, PART 14 - Bandwidth Allocation").


[This message has been edited by pauluk (edited 12-21-2004).]

My school eventually merged the PA system with the PABX. Each classroom had a basic nortel meridian phone on the wall. However, you couldn't make any out going calls, (including internal ones) without a user ID and pin.

and harassing the secretary wasn't advisable!

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Re cable radio:
As digital cable replaces the old analogue services here, it's begining to be severely watered down (to just a few channels) or disappearing altogether (depends on the cable provider)

Parts of Cork's analogue cable network are very old and occasionally, due to insulation leaks, cable FM ends up on air and interferes with normal FM broadcasts! (in a very limited area near the leak)

From what I can tell, due to Sky Digital (satellite)'s dominance, Chorus, the local cable company, is loosing customers very rapidly. Last year it effectively went bust and was taken over by Liberty Media. The falling customer numbers and subsequent lack of income means that the network is starting to suffer rather badly from lack of investment.

It's quite possible that some of those cable cos will just disappear.

[This message has been edited by djk (edited 12-22-2004).]