[time-nuts] 0MHz distribution...NOT

[Mark Spencer]

The attached file should give you an idea of what I have observed when using daisy chained equipment.

The horizontal axis of the graph represents seconds (1 reading per second) the vertical access represents the time difference in nano seconds between an OCXO and a GPSDO that is daisy chained with other devices.  The blips are associated with equipment being powered off and on that is daisy chained to the GPSDO.  As a control I also repeated the experiment using another OCXO as a signal source (in lieu of the GPSDO) and did not see the phase jump when the same equipment was power cycled.  The GPSDO is located in another room and fed from another circuit thru a UPS so I'm confident it's not being somehow influenced via power fluctuations by the other equipment being turned off and on.   I made the measurements with an HP5370B which is also powered via a UPS.

If anyone would like more details or can't view the file please let me know.

Regards
Mark Spencer


--- On Mon, 3/12/12, Bob Bownes <bownes at gmail.com> wrote:

> From: Bob Bownes <bownes at gmail.com>
> Subject: Re: [time-nuts] 0MHz distribution...NOT
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Received: Monday, March 12, 2012, 5:43 PM
> What, if any, are the phase changes?
> 
> 
> On Mon, Mar 12, 2012 at 5:39 PM, Chuck Forsberg WA7KGX
> N2469R
> <caf at omen.com>wrote:
> 
> >
> >
> > On 03/10/2012 04:44 PM, Mark Spencer wrote:
> >
> >> I've done this as well.
> >>
> >> I daisy chained several pieces of hp and marconi
> gear together that all
> >> had an approx 1k ohm input impedance for the
> frequency reference and fed
> >> them from a single 10 Mhz source via t connectors
> with a 50 ohm terminator
> >> at the end of the line.   Looking at
> the signal with either a scope or a
> >> time interval counter I have seen noticeable phase
> shifts when some of the
> >> equipment receiving this signal is turned off or
> on.   That being said so
> >> long as the equipment was not turned off or on the
> adev of the signal was
> >> as expected.   Your mileage may
> vary.
> >>
> >> Sent from my iPad
> >>
> >> On 2012-03-10, at 4:24 PM, Michael Blazer<mblazer at satx.rr.com> 
> wrote:
> >>
> >>  You may want to take a look at the signal on
> a scope.  Most instruments
> >>> terminate their reference input.  You
> might actually have 4 50 ohm loads on
> >>> the Thunderbolt's output and the input voltage
> might be marginal.  If your
> >>> instruments have both reference input and
> output, it's better to daisy
> >>> chain the units.
> >>>
> >>>
> >>> On 3/10/2012 5:10 PM, Chuck Forsberg WA7KGX
> N2469R wrote:
> >>>
> >>>> A month or two ago I had sketched out a
> simple distribution amp
> >>>> for my 10 MHz
> reference.   In the meantime I became
> somewhat
> >>>> disillusioned about my FE-5680a
> standards.   So I removed the
> >>>> FE-5680a and disconnected its power supply
> from the box that
> >>>> holds the Thunderbolt, power supply, and
> big line filter.
> >>>>
> >>>> I decided to try daisy-chaining the
> Thunderbolt's 10 MHz output.
> >>>> I have plenty of hardware left over from
> the days of 10BaseT networking.
> >>>>
> >>>> So I have the Thunderbolt going to a BNC T
> on the back of my FlexRadio
> >>>> 1500,
> >>>> hence to my Advantest U3641 spectrum
> analyzer, and finally to the
> >>>> external
> >>>> reference on my Racal-Dana 1992 nanosecond
> universal counter.  That end
> >>>> has a 50 ohm termination on the other side
> of its T connector.
> >>>>
> >>>> All three devices seem happy with the 10
> MHz they are receiving.
> >>>>
> >>>>  I connected my Tek 2712 to the end of
> the chain.  It reads +10dbm
> > +-1db.
> >
> > Switching units on/off/ext ref causes less than 1db
> change in the 10 MHz.
> >
> >
> >
> > --
> > Chuck Forsberg WA7KGX N2469R     caf at omen.com   www.omen.com
> > Developer of Industrial ZMODEM(Tm) for Embedded
> Applications
> >  Omen Technology Inc      "The High
> Reliability Software"
> > 10255 NW Old Cornelius Pass Portland OR
> 97231   503-614-0430
> >
> >
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