[time-nuts] Re: Efratom LPRO-101 Rubidium question....

[Dan Kemppainen]

Dana,

Just curious, can you share some details on what you are using for the 
IQ demodulator? Is this a 'roll your own' solution Gilbert cell mixer, etc?

Thanks,
Dan


On 8/23/2021 3:30 AM, time-nuts-request at lists.febo.com wrote:
> Message: 4
> Date: Sun, 22 Aug 2021 10:16:56 -0500
> From: Dana Whitlow<k8yumdoober at gmail.com>
> Subject: [time-nuts] Re: Efratom LPRO-101 Rubidium question....
> To: Discussion of precise time and frequency measurement
> 	<time-nuts at lists.febo.com>
> Message-ID:
> 	<CADHrwpeyiqA1PWRVtB_HTmzc8Oxe-wr+fZYz4oZ4VUcnc4h8bQ at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
> 
> C'mon guys- when you speak of a frequency error in Hz, you should also
> specify "at
> what frequency"*in the same breath*.  Or better yet, always specify
> frequency errors in
> relative terms.
> 
> Hundreds of Hz at 10 Mhz is unthinkable for a Rb.   Even at 8.2 GHz, 100 Hz
> error is about
> 12E-9, which is likely to be outside the EFC tuning range of some (if not
> most) Rb standards.
> Both of my Rbs have a tuning range of only roughly 2E-9 via the EFC input.
> Outside that
> range, much sterner measures must be taken, which I frankly dread.
> 
> The two Rbs that I own (an L-Pro and a PRS-10) both tend to drift upwards
> in frequency
> to the tune of about 1E-11 or 2E-11 per month.  Superimposed on that are
> random
> variations of around 1E-11 on a time scale of a few hours.
> 
> I make phase comparisons between the 10 MHz outputs of a GPSDO and the Rb
> under
> test using a simple quadrature demodulator, with the I & Q outputs
> displayed on a 2-chan
> DSO.  I use the "roll mode" display feature on the DSO at its slowest speed
> (1000 sec/div)
> and just leave things running continuously for up to several days.  On my
> DSO a full screen
> width is 14000 sec (slightly under 4 hours), and I just take a glance from
> time to time as I
> happen to pass by.
> 
> Someone suggested a 100 sec measurement with a counter, but that is right
> in the realm
> where GPSDOs are typically the most noisy, so a single measurement is
> likely to have
> rather large errors.  One would have to record a fairly large number of
> such measurements
> (several hundreds of them) and plot them out to get a good assessment of
> what the Rb is
> actually doing.  WIth the IQ phase difference display, one can get a pretty
> decent estimate of
> the needed tuning correction, without doing any real work at all, in a day
> or so.
> 
> When I'm doing something requiring the best frequency accuracy, I keep the
> 'scope display
> running while I'm doing the serious work, and note the frequency error of
> the Rb at the time
> for use in correcting the final result.  BTW, I don't see much "settling"
> effect after making
> tuning changes- the correction made seems to take effect essentially
> immediately (as best
> as one can tell in the presence of GPS noise).  By comparing two Rbs, I can
> investigate
> settling effects quite well without the noise having anything to do with it.
> 
> Dana
> 
> 
> On Sun, Aug 22, 2021 at 8:41 AM Matthias Welwarsky<time-nuts at welwarsky.de>
> wrote: