[time-nuts] Mechanical 1PPS Oscillator Disciplining

[Alan Melia]

Hi Tom dividing down wasn't always necessary I have sample from the UK  GPO 
Crystal Factory of NT-cut bars, quartz tuning fork, and Gapped Ring 
crystals, the latter marked 400cps (pre Hertz :-))  )  I think these are 
post WWII because they are mounted in IO base GT style tube envelopes. 
Dividers were achieved with neons and locked multivibrators, where 
necessary, I believe.

The original ( 1926 ) frequency source for Rugby GBR  16kHz radio station 
was an invar tuning fork with a tube maintaining amplifier. I cannot find 
any information on syntonising that but it probably was not necessary.
Alan
G3NYK


----- Original Message ----- 
From: "Tom Van Baak" <tvb at LeapSecond.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Friday, January 09, 2015 9:51 PM
Subject: Re: [time-nuts] Mechanical 1PPS Oscillator Disciplining


> Andy,
>
> Yes, Neal Stephenson's Mother Earth Mother Board article is a classic that 
> every time nut should read at some point.
> The "one page" version is at 
> http://archive.wired.com/wired/archive/4.12/ffglass_pr.html
>
> Prior to quartz, pendulum clocks and tuning fork oscillators were the 
> standard. Even until the 1950's or early 1960's tuning fork oscillators 
> were used when one needed accurate frequency in the audio range. That's 
> because dividing down high frequency quartz oscillators to, say, 60 Hz or 
> 400 Hz required lots of circuitry. Not sure if Neal's reference to 
> "vibrating reed" is what we would call a tuning fork, or if it's something 
> else.
>
> Here in the US General Radio made precision tuning fork oscillators. Model 
> numbers 213, 723, 813, 815. One example is at 
> http://leapsecond.com/museum/gr815b/
> Also check out old issues of "General Radio Experimenter" magazine for 
> details on these wonderful instruments.
>
> Pendulum clocks were also used in power plants around the world to keep 
> the grid synchronized. There is occasional discussion about this on clock 
> collecting or horology forums. They are precious and can be extremely 
> accurate, as good as a second a year.
>
> Since pendulum clocks were better long-term timekeepers and generated only 
> 0.5 or 1 Hz signals, a PDTF (Pendulum Disciplined Tuning Fork) made sense. 
> Has a nice ring to it, doesn't it.
>
> /tvb
>
> ----- Original Message ----- 
> From: "Andy Bardagjy" <andy at bardagjy.com>
> To: "Discussion of precise time and frequency measurement" 
> <time-nuts at febo.com>
> Sent: Friday, January 09, 2015 9:22 AM
> Subject: [time-nuts] Mechanical 1PPS Oscillator Disciplining
>
>
> From a fascinating (albeit long) article about transatlantic communication 
> cables
>
> http://archive.wired.com/wired/archive/4.12/ffglass.html
>
> On the bottom of page 45 to the top of page 46
>
> "Each piece of equipment on this tabletop is built around a motor that 
> turns over at the same precise frequency. None of it would work - no 
> device could communicate with any other device - unless all of those 
> motors were spinning in lockstep with one another. The transmitter, 
> regenerator/retransmitter, and printer all had to be in sync even though 
> they were thousands of miles apart.
>
> This feat is achieved by means of a collection of extremely precise analog 
> machinery. The heart of the system is another polished box that contains a 
> vibrating reed, electromagnetically driven, thrumming along at 30 cycles 
> per second, generating the clock pulses that keep all the other machines 
> turning over at the right pace. The reed is as precise as such a thing can 
> be, but over time it is bound to drift and get out of sync with the other 
> vibrating reeds in the other stations.
>
> In order to control this tendency, a pair of identical pendulum clocks 
> hang next to each other on the wall above. These clocks feed steady, 
> one-second timing pulses into the box housing the reed. The reed, in turn, 
> is driving a motor that is geared so that it should turn over at one 
> revolution per second, generating a pulse with each revolution. If the 
> frequency of the reed's vibration begins to drift, the motor's speed will 
> drift along with it, and the pulse will come a bit too early or a bit too 
> late. But these pulses are being compared with the steady one-second 
> pulses generated by the double pendulum clock, and any difference between 
> them is detected by a feedback system that can slightly speed up or slow 
> down the vibration of the reed in order to correct the error. The result 
> is a clock so steady that once one of them is set up in, say, London, and 
> another is set up in, say, Cape Town, the machinery in those two cities 
> will remain synched with each other indefinitely."
>
> Does anyone know any other history about that particular piece of 
> equipment?
>
> Cheers!
>
> Andy ◉ Bardagjy.com ◉ +1-404-964-1641
>
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