[time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
kb8tq at n1k.org
Fri Jun 2 20:04:18 EDT 2017
> On Jun 2, 2017, at 7:45 PM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
> 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.
>> On Friday, June 2, 2017, Bob kb8tq <kb8tq at n1k.org> wrote:
>>> 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.
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