[time-nuts] hp10811-60111 on ebay

[Steve Rooke]

On 30 June 2010 02:46, Attila Kinali <attila at kinali.ch> wrote:

>> That would be the sort of gadget which would allow you to compare what
>> ocxo devices you have. If you have a dedicated spectrum analyser that
>> would allow you to look directly at phase-nose. There are a number of
>> ways to determine such "quality" measurements and not all of them
>> require a hefty outlay in test equipment. I wonder what you are trying
>> to achieve with your search for a good ocxo as this may indicate what
>> path is best for you.
>
> My goal is to build a GPSDO and to learn as much as possible
> in the process. And while i'm at it, i'd like to get a
> precission/accuracy that comes close to what can commercially
> bought, if possible even better ;-)

Are you planning on building one of the published designs or coming up
with something of your own? If your really interested in this field
you probably going to look at investing in at least a minimum of
equipment that will produce accurate results. If you don't already
have a good counter, I would suggest you start looking out for one in
the usual places as if you search for a prolonged period you stand to
pick up something at the "right" price for you. Get one that is as
stable as you can afford and make sure it has some form of instrument
buss. This would allow you to perform ADEV measurements either
directly, if the counter is able to pre-trigger on a stop event, or
you can perform a test using the picket fence method. Of course, you
may be able to build up your own version of the TPLL setup using a
phase detector and VtoF converter feeding into your sound card to
count the number of cycles over a minimum tau period. Of course, this
is a chicken and egg situation as you need a good reference oscillator
to start with and if you have nothing so far then this will not work
for you. There is the delay line method which only requires a single
oscillator, the DUT, where you spit the oscillators output with a
power divider or directional coupler and then pass one output through
a delay line that is calculated to end up with the signal being 90
degrees out of phase with the undelayed version. Those two signals are
then fed to a phase detector, through a low pass filter and to some
method of measuring the residual components present. The product of
the two out of phase signals to the phase detector will cancel out
producing 0V when they are exactly 90 degrees apart but any other
frequencies present will not be at 90 degrees so they will show up on
the output. You could use this to simply compare sources without
having absolute measurements, IE. simple test measurements, or obtain
referenced measurements with appropriate equipment.

> And as most of the parameters of the GPSDO are dictated by the
> quality of the OCXO, i'd like to get some that are of good quality.
> Or at least worth the money i pay for them.

Without buying something off the shelf with a manufacturers test cert,
you will have to start somewhere and choose an ocxo that should give
you the best performance that your wallet can provide on the used
market. The 10811 is a very well known and respected unit which comes
in two basic variants, the single oven which has tuning screws and the
double oven which does not. Obviously the double oven will perform
better with a change in temperature but the jury is undecided on which
is better wrt the ADEV performance. Buying a well used xtal should
give you much better performance than a new one which has not been
run-in.

To start from scratch and produce a top quality performance GPSDO at
the first try is quite a goal to reach but in performing the task you
will learn a great deal about the subject and how you can improve
things in the future. There is no reason why you cannot update the
ocxo in your GPSDO later on when you find a better one as I think you
will need to look at how your going to test these before you can
achieve the best performance. Of course, you may be able to buy a used
fully tested ocxo with tested ADEV if you can find someone who would
sell that to you. Maybe someone on this list could help you out there.

I have not expanded on the ideas above but if your interested I'm sure
others or myself can come up with some useful links to assist you and
help as well.

Steve

>
>                        Attila Kinali
>
> --
> If you want to walk fast, walk alone.
> If you want to walk far, walk together.
>                -- African proverb
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 
Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
- Einstein