[time-nuts] How Rubidiums make their frequency

[Magnus Danielson]

From: "Dave Brown" <tractorb at ihug.co.nz>
Subject: Re: [time-nuts] How Rubidiums make their frequency
Date: Thu, 20 Apr 2006 09:13:08 +1200
Message-ID: <03dd01c663f6$0e8dda80$7900a8c0 at athlon1200>

> 
> ----- Original Message ----- 
> From: "Matt Ettus" <boyscout at gmail.com>
> To: <K3IO at verizon.net>; "Discussion of precise time and frequency 
> measurement" <time-nuts at febo.com>
> Sent: Thursday, April 20, 2006 7:55 AM
> Subject: Re: [time-nuts] How Rubidiums make their frequency
> 
> 
> > Since we can now make DDS's with arbitrary frequency resolution, 
> > could
> > you make an Rb oscillator without the magnetic field adjustment?
> 
>  snip---
> 
> I suspect the FEI 5650 series does just that- a 50.255+ MHz VCXO is 
> 'locked' at 1/136 of the 6.8GHz Rb resonance and there is no 'user' 
> adjustment provided for the physics package.  I suspect the magnetic 
> field IS preset in the factory but thereafter intended to be left well 
> alone.

Well, first of all they state that it is 1/136 and yes it is preset put
available as a controlable thing as an option. See their sales-material and
you find it (I did):

http://www.freqelec.com/

>  The 50.255+ VCXO drives an AD9830-all fine tuning of the output 
> frequency takes place by setting the DDS.
> Can anyone comment further on this?
> 
> On a related issue- the physics package in these units draws a 
> significant current at startup- I'm considering current limiting the 
> suppy until the current drops back to a lower value-I guess this 
> delays the warmup somewhat but it would reduce the current required 
> from the supply to the steady state value, for example, thus allowing 
> a smaller power supply rating.

I would not do that. However, the heater supply isn't as critical so it would
allow itself for a very simple supply anyway.

Cheers,
Magnus