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    Hard wired bells and pulse dialing supported?

    This is a discussion on Hard wired bells and pulse dialing supported? within the Sky Talk forums, part of the Other Sky help and support category; Hello, Soon to move over to Sky Talk, and we have a hard-wired bell (proper loud thing) which was installed ...

    1. #1
      hivemind's Avatar
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      Hard wired bells and pulse dialing supported?

      Hello,

      Soon to move over to Sky Talk, and we have a hard-wired bell (proper loud thing) which was installed some time in the early '80s. It has been working fine using BT for line rental and Be for broadband.

      Does Sky still support bell/ring wire? And, while I'm here, does it support pulse dialing (that one more for curiosity...)? Thanks.

      ETA Just had a proper look at it, I think it's a Bellset 50C - anyway, 2x2000 ohm ringers, with green+orange+blue wires entering the box, but only orange+blue connected (aren't they the colours for the speech wires?).
      Last edited by hivemind; 15-02-14 at 03:42 PM. Reason: more info


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      Re: Hard wired bells and pulse dialing supported?

      The signal on the ring wire is generated by a capacitor in the master socket, it is not connected all the way back to the exchange, so there is no reason that it shouldn't work just the same on a Sky telephone system. It was only used to make the old round dial type phone extensions ring. Be warned though having this wire connected creates interference which can have a major impact on broadband speeds and performance.
      I have no idea if the pulse dialing is still supported I guess there might be a few people about with the old clicky dial type phones still.

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      Re: Hard wired bells and pulse dialing supported?

      The ring wire is still 'supported' but if you don't already have one you should fit a ADSL/vDSL filter, both of which filter the ring circuit. The problem with using pulse dialling is that you will be unable to use certain functions. eg, many service calls require you to press digits for alternative enquiries, called a phone tree. There is also a good chance that Sky's fully automated system may not support pulse dialling. Pulse dialling started to be phased out in the 70s in favour of DTMF(touch tone) dialling, the vast majority of phones now use this system.

      TomD


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      Re: Hard wired bells and pulse dialing supported?

      Koala5 and Isitme, thanks. OK this has kicked me to trying to understand what goes on in the master socket, so I am staring at this diagram: UK Telephone Wiring (underneath "The Wiring"). This is for curiosity purposes, and I have only vague amateur understanding of electronics, so anyone shout at me if I am getting things wrong.

      - Spark gap exists to short-circuit on momentary voltage surge, protecting customer equipment.

      - When things are idle, A/J5 = tip/earth = 0 V, B/J2 = ring/battery = -50V DC (although other places say the other way round, although apparently /usually/ it doesn't matter).

      - Ringing involves a superimposed 20Hz AC voltage across A/B of something like 40-60V RMS.

      - That capacitor, which from reading elsewhere is actually 1.8uF, gives >3.5kOhm reactance at ringing frequency (~20Hz), but <300 Ohm reactance at voice frequencies (300Hz+). Is latter irrelevant as far as triggering the bell because off-hook voltages are comparatively low?

      - Traditional AC bells are fitted between J3 and J5, so it gets the AC component but not DC. I suppose 1.8uF also means >10 kOhm reactance to ~8Hz pulse dialing, so less likely to hear tinkling (see also below).

      - The 470k resistor provides a high impedance closed circuit, so AC tests can be applied to the line even when no equipment is connected.

      - Why create separate ring wire at entry point:
      1) Multiple bells were traditionally wired in series. They could be wired up in parallel directly to J2/J5 (A/B) each with their own capacitors, but too many of them would draw significant current;
      2) No need to repeat historically bulky capacitors;
      3) (read this somewhere, but without explanation) Somehow assists anti-tinkling circuitry in phones during pulse dialing.

      Does this sound vaguely right?

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      Re: Hard wired bells and pulse dialing supported?

      Mmmm you are probably about right! It's about 25 years since I had anything to do with resistors and capacitors so I'm a bit bit rusty, but I suspect like you say the capacitor is to make sure just the ring signal gets to the bell and nothing else.

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      Re: Hard wired bells and pulse dialing supported?

      Impulse dialling does still work as illustrated by this post:
      http://www.skyuser.co.uk/forum/sky-t...tml#post429008
      As for your query about the bell, without getting too technical:

      • Bells were connected in series because the magnetism required to ring the bell depended on current so connecting all bells in series ensured that they all had the same current flowing through them and if correctly adjusted would be equally loud.
      • Some extensions had a bell On/Off switch which shorted out the bell coils ensuring that ring current could still flow through the remaining bells.
      • The exchange recognises an off hook condition by a direct current flow through the subscribers instrument back to the -50V battery at the exchange.
      • Without a DC blocking capacitor the low impedance bell coils would cause this condition.
      • As well as the impulsing contacts a rotary dial has "off normal" contacts which shorted out the bell and voice circuits during impulsing.
      • This served to eliminate bell tinkling and loud clicks in the earpiece as well as preventing distortion of the dialling pulses.
      • A fourth "anti tinkling" wire (no longer used) applied the benefits of these contacts to the other telephones connected to the same line.

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      Re: Hard wired bells and pulse dialing supported?

      OK, that had made things clearer, thanks - and you don't want DC flowing through the low impedance bell coils all the time anyway. I suppose the bells are not immediately silenced when going off-hook because some applications require off-hook ringing. Was the fourth wire just J3=bell straight from the master box/socket without passing through other bells, i.e. all bells silenced by shorting this to J5=earth?

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      Re: Hard wired bells and pulse dialing supported?

      The series model either used hard wired connections or a round jack plug with tip, three rings and a sleeve ie. five contacts giving a&b (the speech pair), bell in, bell out and anti-tinkle.
      I don't remember the contact layout. A break contact separated bell in and bell out when the plug was inserted allowing the series bell to be included in the circuit.

      The bells changed to parallel connection at the same time as the new (now standard) BT telephone plug was introduced. When fitting the new plug existing telephones required a 3.3KΩ resistor to be fitted in series with the bell coils to prevent excessive loading when more than one instrument was connected in parallel though new telephones had high impedance bell coils fitted as standard.

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