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" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
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" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
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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