Re: 1956 -- circuit reliability book

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#619782

From: si... Simon Turner
Date: Wed, 07 Feb 2018 10:30

39 lines
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On Tuesday, in article
     <8b68e11e-5b32-4e00...@googlegroups.com>
     hanc...@bbs.cpcn.com wrote:

> On Tuesday, February 6, 2018 at 4:55:35 AM UTC-5, Andy Burns wrote:
>> Simon Turner wrote:
>> 
>>> I have no experience of US phone bells, but UK ones certainly don't
>>> sound right if they are rung with the wrong frequency (50 Hz from the
>>> mains rather than the 25 Hz they are expecting)
>> 
>> I thought they were 17Hz?  Though it's a long time since I heard a phone 
>> with a bell, apart from as an MP3 ringtone ...
> 
> In the U.S., landline ringer frequency is 20 Hz.

In the UK, it's now 25 Hz; 17 Hz (actually 16 2/3 Hz) was the old GPO
ringing frequency, but it's been 25 Hz for many years (I haven't managed
to find a reference to exactly when this happened, or whether it was
gradual as exchanges were upgraded, but have seen the 60s-70s suggested
as a time frame).

Strictly, it's 25 Hz +1 Hz, -5 Hz, according to BT Suppliers'
Information Note 351 ("Technical Characteristics Of The Single Analogue
Line Interface"), Annex A:

  http://www.sinet.bt.com/sinet/SINs/pdf/351v4p8.pdf

A bell phone ringing at 16 2/3 Hz would probably have sounded noticeably
different from the 50%-faster 25 Hz (I'll have to modify my ringer and
see), but 50 Hz definitely doesn't sound right at all.

As an aside, I wonder if it's a coincidence that both the old UK 16 2/3
Hz ringing signal and the US 20 Hz are one third of mains frequency...

-- 
Simon Turner                                    DoD #0461
si...@twoplaces.co.uk
    Trust me -- I know what I'm doing!          -- Sledge Hammer

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From: si...@twoplaces.co.uk (Simon Turner)
Newsgroups: alt.folklore.computers
Subject: Re: 1956 -- circuit reliability book
Date: Wed, 07 Feb 2018 10:30:49 +0000 (GMT)
Organization: Two Places in Time
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