[time-nuts] Checking accuracy of Rubidium standards

[Alan Melia]

This is an interesting thread again.....it may be similar to ones that have
been discussed, but one or two furthur questions occur to me. I have a
Montronics sytem that does comparisons by the multiply and mix process, and
I find (also common to more modern Kethly systems) that the limitation is
around a part in 10^10 where the noise on the phase output makes it not
really usable (without a lot of averaging) being around or in excess of 90
degreees even with a couple of very good OXCOs. How does the 10G comparision
avoid this problem with standard multipliers? I doubt you can go all that
way with low-noise multipliers and have any useful signal left, or have I
missed something. At present I use a phase meter (lock in amps can be quite
good) at the MHz range and datalog the phase drift for several hours. I have
determined that setting "on the nose" is not necessary (for my
applications). It is more useful to know how far a source is "off".
How does the mix down compare with the seemingly more popular "mix down and
timestamp" I understand from previous threads that this has more potential
but might it also be as good even using simpler circuits that the NIST
system.

Thanks for all your efforts inthe background John..... great reading
material !

Alan G3NYK

----- Original Message -----
From: "Jeffrey Pawlan" <jpawlan at pawlan.com>
To: <hamradio at oz.net>; "Discussion of precise time and frequency
measurement" <time-nuts at febo.com>
Sent: Saturday, November 08, 2008 6:40 PM
Subject: Re: [time-nuts] Checking accuracy of Rubidium standards


>
>
> On Sat, 8 Nov 2008, Randy wrote:
>
> > I was wondering if it is worthwhile or even feasible to compare an LPRO
> > Rubidium standard against a Z3801.  Since their frequencies are probably
> > going to be extremely close anyway it would seem some special
> > method/equipment would be required for high precision.  Suggestions?
> >
> >
> > Randy, W7HR
> > Port Orchard, WA
>
> The best way would be to compare the highest possible frequencies you can
> generate with these two sources. I use two 10GHz sources that are each
phase
> locked to an external 10MHz reference. Then the 10GHz outputs can be
compared
> using either of these easy methods:
> 1) look at the DC/IF output of a microwave mixer where the LO and RF ports
are
> driven by the two 10GHz sources. Don't overdrive the RF input to a level
that
> can burn out your mixer.
>
> 2) use a good microwave frequency counter to read one of the 10GHz outputs
while
> driving the counter's 10MHz ext ref input with the 10MHz from the other
10MHz
> source. This is very fast but will only give you accuracy readings that
are a
> function of the resolution of the counter plus the bounce of the last
digit
> owing to sampling and triggering.
>
> 3) if you have access to a lab with one or two microwave synthesized
signal
> generators, then you can apply the 10MHz sources to the ext ref inputs of
each
> of these signal generators and then proceed as in 1) or 2)
> I have done comparison at 26GHz this way so I have a bit more resolution.
>
> 73,
>
> Jeffrey Pawlan  WA6KBL
>
>
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