[time-nuts] GPS and Rubidium frequency standards and noise question (newbie).

[Jim Lux]

On 6/2/12 2:57 PM, Chris Wilson wrote:
>
>
>    I am looking to get a frequency standard for my amateur radio shack,
>    initially for verifying test gear readings, but later as a standard
>    to lock receiver and transmitter oscillators to. I was going to buy
>    a GPS frequency standard but a friend warned me these may have noise
>    issues when I come to use it with an oscillator in RX / TX
>    applications. It's not something I had considered, so what's the
>    score here please? Should I not buy a GPS standard? Thanks. Any
>    links to known safe suitable purchase sources from personal
>    experience welcome, either here or by PM or e-mail. I am in the UK.
>

What's your need, frequency accuracy wise?
What's your phase noise requirement?

The first thing to look at would be an ovenized quartz oscillator. 
They're stable (aging rate is around 1E-10/day.. ) and pretty quiet 
(-165 dBc at 10kHz out).  They run $50-100 on eBay or similar, and are 
pretty easy.. you hook up a 12 or 15V DC power supply and they put out 
10 MHz..  Like an old HP 10811 or a Wenzel Streamline would do you nicely.

(BTW, a lot of test equipment has a decent oscillator inside.. so you if 
you got a suitable counter or signal generator, surplus, that has a good 
oscillator, then you just use the reference output from the instrument. 
  Ask on this list about candidate instruments)

if 1E-10/day isn't good enough... (maybe you're doing microwave 
hilltopping every 6 months.. 1E-10/day would be 0.01 ppm, so your 10GHz 
signal would be off by 100 Hz every time you went out)

Then, a GPS disciplined quartz oscillator (any of several kinds are 
available surplus or cobble one together yourself) is probably your best 
bet.   Even without the GPS signal, it will typically be pretty quiet 
and stable (because basically it's an ovenized XO).  HP Z3801As used to 
be common, Trimble Thunderbolts are more recent, etc.


A Rb source (bunches of these on the surplus market recently) is another 
choice.  Just like the GPS, they usually are disciplining a quartz 
oscillator, so the output spectral purity is really that of the quartz 
oscillator. Advantage of a Rb is that it works indoors or underground 
where there is no GPS.  And, it's accurate sooner after applying power 
in most cases.   But they DO age, and you need to adjust them  (still, 
pretty good.. aging might be 1E-8 over 20 years. )
The lamp wears out too, so a 25 year old surplus Rb might be near end of 
life (or might not).

google the FS725 for an example of what a current inexpensive Rb 
reference looks like.  Surplus, the internal source can be in the $100 
range, but you'll have to cobble up a power supply, and probably modify 
some connectors.  This list has lots of people who can give you advice 
on this, though.

But it gets back to.. how good do you need?