External adjustment makes it very easy to adjust as you have
access to the adjustment voltage to measure it, and even a 1K
multi-turn wirewound pot would give around 1E-12 setting resolution.
The sensitivty of the EFC is only around 1E-12 per mV, so it is
much less sensitive to temperature stability than quartz oscillators.
A temperature coeff of +/- 20ppm /degC with an EFC voltage of 2.5V
would only contribute around +/-5E-14 /degC frequency change.
By adding fine adjustment or a DAC, you can get way below 1E-13
setting resolution. The only problem here is that environmental
conditions such as variations in temperature and pressure do affect Rb
oscillators and the EFC circuit, and can change the frequency by 1E-13
in a matter of minutes. Still, it's useful to be able to do it for
disciplining, or if the environmental conditions are being controlled
or compensated for. The ADEV of an LPRO can be around 1E-13 or so at a
tau of hours, so even a step size of 1E-13 can be rather too coarse,
especially if the environmental effects have been minimised.
It would be nice to find a relatively simple and inexpensive 10MHz
synthesizer that has a resolution of closer to 1E-14 to avoid messing
with the EFC at all.
Angus.
On Fri, 25 Jul 2008 20:33:26 -0400, you wrote:
>If I choose to control the frequency via External C-field control I guess it
>would take a very precise and stable voltage source. Any thoughts or
>suggestions?
>
>----- Original Message -----
>From: "Scott Mace" <[EMAIL PROTECTED]>
>To: "jshank" <[EMAIL PROTECTED]>; "Discussion of precise time and
>frequency measurement" <time-nuts@febo.com>
>Sent: Friday, July 25, 2008 7:15 PM
>Subject: Re: [time-nuts] LPRO 101 ADJUSTMENT
>
>
>> Both methods work well. Be sure the unit is mounted to some sort of
>> heatsink,chassis, etc.
>> I'm using a Fury GPS receiver to drive the EFC on an LPRO-101.
>> You won't get much range out of either adjustment. Leave it powered
>> on for a couple of hours before trying to adjust it. I usually set the
>> trim pot in the
>> middle of it's range and use the EFC pin. I think it's a 28 or 30 turn
>> pot. EFC
>> is 0-5v. The unit will self-bias to around 2.5v if the EFC pin is open.
>>
>> Scott
>>
>> jshank wrote:
>>> Hi,
>>>
>>> I recently acquired a LPRO 101 Rubidium Oscillator. After reading the
>>> manual I see that there are two ways to adjust the frequency 1) using and
>>> adjusting screw on the unit and 2) using the External C-field control
>>> signal at pin J1-7. Has anyone experimented with either method and if so
>>> what method was preferred?
>>>
>>> Jeff
>>>
>>>
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>
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