[time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies

Donald E. Pauly trojancowboy at gmail.com
Fri Jun 2 19:45:36 EDT 2017


Electronic thermal coolers did not exist then so it could not be done.
Electronic temperature sensors did not exist either.  That crystal cut
has been known since the 1940's at least.  It has been neglected
because of limited temperature range. It yields ±1 ppm over a range of
±20° C from 25° C.  A slightly different angle of cut can yield ±250
ppb over that range. (4:1 improvement) Contrast that with a normal AT
cut which yields ±9 ppm over that range.

I built an oven with an Analog Devices temperature sensor 20 years
ago.  I did not have time to incorporate foam insulation.  The heater
power was not available to run it at 65° C without insulation.  It had
to run at 40° C and it would hold about 1 ppb over a few hours.   It
would hold the crystal within 0.01° or so but it was far away from the
turnover temperature.   Convection currents cause problems.  It
convinced me that ovens were headaches.   Thermal coolers remove most
of these.


---------- Forwarded message ----------
From: Bob kb8tq <kb8tq at n1k.org>
Date: Fri, Jun 2, 2017 at 3:50 PM
Subject: Re: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Cc: "rward0 at aol.com" <rward0 at aol.com>, "Donald E. Pauly"
<trojancowboy at gmail.com>


Have you checked out the papers from the 1950 and `1960’s where they
actually tried what you
propose with essentially the same parts you are looking at using?


> On Jun 2, 2017, at 5:51 PM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
> # 2 is not true.  A cut has either two turning points or zero.  Where
> both turning points exist there are two temperatures at which the
> temperature coefficient of frequency is zero.  Cut 0 on figure 6 at
> https://coloradocrystal.com/applications has no turnover point.  It is
> neither fish nor fowl.  Cut 6 is the normal AT curve with extremes of
> ±16 ppm for -55° C thru +105° C.  All curves normally intersect at 25°
> C rather than the 27° C shown.  25° C is half way between -55° C thru
> +105° C.  Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0
> is y=4x^3.
> Consider the standard AT cut which has turnover points at -15° C and
> 65° C.  The lower turnover would ordinarily not be used in ovens.  A
> set point error of ±1° C in the upper turnover point at 65° C results
> in a frequency error of +14.875·10^-9.  For cut 0, that same ±1° error
> in room temperature results in a frequency error of  ±31.25·10^-12.
> This is an improvement of 476 to 1.  You apparently have not thought
> thru what improvements are possible with thermal coolers/heaters.
> Among these is near instant warm up and greatly reduced power for
> thermal management.
> πθ°μΩω±√·Γ
> On Friday, June 2, 2017, Bob kb8tq <kb8tq at n1k.org> wrote:
>> Hi
>> Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
>> the temperature will be a bit different and you will match your oven to it. If you attempt a zero
>> angle cut, you will never really hit it and there is no way to compensate for the problem.
>> Bob
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