# [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies

Bob kb8tq kb8tq at n1k.org
Sun Jun 4 08:15:03 EDT 2017

```Hi

Have you ever tried to actually *buy* a crystal built to a specification? There is a
tolerance on them. That has a profound impact on what you can *buy*.

Bob

> On Jun 4, 2017, at 12:56 AM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
>
> You have a fundamental misunderstanding of the AT curve family.  See
> my QBASIC plot at
> http://gonascent.com/papers/hp/hp5061/photos/newxtl.jpg .  The
> commonly described AT cut is shown as the largest sine wave in the
> blue rectangle.  The left side of the rectangle is -55°C, the center
> is 25° C and the right side is 105° C.  The bottom of the rectangle is
> -16 ppm and the top is +16 ppm.
>
> Main Cut
> Temp   Freq
> -55° C -16 ppm
> -15° C +16 ppm
> +25° C ±0 ppm
> +65° C -16 ppm
> 105° C +16 ppm
>
> You can get a lower turnover point of 24° C and an upper turnover
> point of 26° C. Their amplitude would be °±0.250 ppb.  As the turnover
> points approach each other, their amplitude approaches zero.  The line
> joining all the turnover points is y= -8·x^3.  The zero temperature
> for 25° is y=4·x^3.  Practical tolerance these days is on the order of
> 0.1 minutes of arc.  This is within the width of the traces in the
> graph.
>
> You are way off on your 0° to 50° C crystal.
>
> ["Umm …. errr … it’s quite easy to get a +/- 2 ppm 0-50C AT cut
> *including* the tolerance on the cut angle."]
>
> Temp   Freq
>     0° C   -0.488 ppb (lower limit)
> 12.5° C  +0.488 ppb (lower turning point)
>   25° C  ±0
> 37.5° C  -0.488 ppb (upper turning point)
>   50° C +0.488 ppb (upper limit)
>
> As I claimed, a Thermal Electric Cooler has never been used to build a
> crystal oscillator.  In the 50s, TEC efficiencies were on the order of
> 1% and were useless.  The Soviets made coolers more practical in the
> 70s with better materials.  I saw one used at Telemation that was able
> to measure dew point by condensing water vapor on a mirror.  It looks
> like efficiencies have now improved to 33% or so.
>
> It was only in the early 70s that Analog Devices invented the AD590
> solid state temperature sensor.  It made thermister bridges obsolete.
> Switching amplifiers are required to drive thermal coolers if you want
> to preserve efficiency.
>
> πθ°μΩω±√·Γλ
> WB0KVV
>
> ---------- Forwarded message ----------
> From: Bob kb8tq <kb8tq at n1k.org>
> Date: Fri, Jun 2, 2017 at 12:22 PM
> Subject: Re: HP5061B Versus HP5071 Cesium Line Frequencies
> To: "Donald E. Pauly" <trojancowboy at gmail.com>
> Cc: "rward0 at aol.com" <rward0 at aol.com>, time-nuts <time-nuts at febo.com>
>
> 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
>
> On Jun 2, 2017, at 3:19 PM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
>
> A cut at that angle has no turn over temperature. The zero temperature
> coefficient point is 25°.  Its temperature coefficient everywhere else
> is positive.
>
> On Friday, June 2, 2017, Bob kb8tq <kb8tq at n1k.org> wrote:
>>
>> Hi
>>
>> If you are going to use an oven, it’s better to run it at the turn temperature of
>> the crystal. That would put you above 50C for an AT and a bit higher still for an SC.
>>
>> Bob
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```