[time-nuts] Efratom FRK - no 10Mhz oscillator

Wed Jan 4 18:34:19 UTC 2012

If you have GPSDOs than no need to walk (if not for your health). As
already told here, GPSDOs are the best reference we can have and, in the
long run, even better than Cs. Use your GPSDOs as a reference and go for a
walk without the Rb: clocks must stay quiet.

On Wed, Jan 4, 2012 at 6:41 PM, <lists at lazygranch.com> wrote:

> At the old HP Santa Clara office, they had a cesium clock in the lobby. I
> was told the 10MHz reference for the facility came from that clock.
> Reality? Who knows.
> -----Original Message-----
> From: "Don Lewis" <dlewis6767 at austin.rr.com>
> Sender: time-nuts-bounces at febo.com
> Date: Wed, 4 Jan 2012 11:35:24
> To: 'Discussion of precise time and frequency measurement'<
> time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency measurement
>        <time-nuts at febo.com>
> Subject: Re: [time-nuts] Efratom FRK - no 10Mhz oscillator
>
> Thanks, all, for your recent help on my Efratom.  I finally got it
> operational.
>
>
>
> The crystal-holder in the [hot] OCXO was bad; one pin looked like it had
> corroded in two.
>
>
>
> I had to dig out the crystal and holder (it was REALLY potted with grey
> RTV.)
>
>
>
> Once I got it all back together, I had to tweak a 'factory-set' small pf
> capacitor in the VCO/varactor circuit; and then it locked after about 5
> minutes.
>
>
>
> Since it is now my only 'standard' I guess I will proclaim myself a true
> TIME-NUT and start seeking an even better standard. I have three Rockwell
> GPS-D200 modules ...maybe tying all three together someway will help me vet
> the rubidium.
>
>
>
> Btw ...Is there any place in Austin, TX I could walk in with the Efratom
> and
> get a 'cesium' check on the Efratom and calibrate it even further???
> Appears it has a trimmer for such.
>
>
>
> -Don
>
> Austin, TX
>
>
>
>
>
>
>
>
>
>
>
>
>
> ............................................
>
>
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Ed Palmer
> Sent: Wednesday, December 21, 2011 12:12 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Efratom FRK - no 10Mhz oscillator
>
>
>
> Hi Don,
>
>
>
> I'm assuming that you've checked for obvious things like bad solder
>
> joints.  After 20 or more years in that heat, anything is possible.
>
> Luckily, the oscillator board doesn't have too many connections to
>
> remove when you pull the board.  I use a 20X magnifier to really get
>
> close.  I've often found problems that you can't see with less
>
> magnification.
>
>
>
> In one message you mentioned that touching the crystal oven with an
>
> external 10 MHz signal starts the oscillator.  Isn't the oven supposed
>
> to be grounded?
>
>
>
> I agree with other posters that if you have a bad crystal, you'll have
>
> to find a replacement that's made to be used in an oven.  However, any
>
> old 10 MHz crystal will be useful to diagnose the problem.  It might be
>
> possible to sacrifice another OCXO and transplant the crystal into the
>
> FRK.  Your best bet would be an OCXO with an AT crystal.  I wouldn't try
>
> using an SC crystal.  The circuitry would be significantly different.
>
> The oven would have to be retuned to match the new crystal, but that's
>
> just a resistor change.
>
>
>
> If you're up for a bigger challenge, you could try interfacing an
>
> external OCXO to the Rubidium loop.  Rubidiums are typically marketed
>
> for low drift applications rather than low Allan Deviation or phase
>
> noise.  I've wondered whether a high quality SC-crystal OCXO would make
>
> a significant improvement in a Rubidium's short-term performance.  I've
>
> never had a Rubidium with a dead oscillator to experiment on.
>
>
>
> Ed
>
>
>
>
>
> On 12/21/2011 8:04 AM, Don Lewis wrote:
>
> > Thanks, Pete.
>
> >
>
> > Good tips.
>
> >
>
> > I ordered 10 crystals this morning, ...they are dirt cheap.  Will try and
>
> > test one as you suggested.
>
> >
>
> > If it is the 'crystal', a bad crystal, .......what then?
>
> >
>
> > Do I try to place one of these cheap ones in the oven, ...or do I try to
>
> > just run it outside the oven or find a high-temperature crystal???
>
> >
>
> > The crystal oven/controller seems fine, ...hot enough to hurt my fingers.
>
> >
>
> > Thanks, ...-Don
>
> >
>
> >
>
> > ------------------------------------------
>
> >
>
> >
>
> >
>
> > -----Original Message-----
>
> > From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>
> > Behalf Of Peter Bell
>
> > Sent: Wednesday, December 21, 2011 5:28 AM
>
> > To: Discussion of precise time and frequency measurement
>
> > Subject: Re: [time-nuts] Efratom FRK - no 10Mhz oscillator
>
> >
>
> > Yeah, that was why I suggested just sticking a random 10MHz xtal
>
> > across the pins on the board (with the existing xtal wiring
>
> > disconnected) - if the rest of the circuit is good, then the
>
> > oscillator should start up with no problems - if it doesn't, then
>
> > suspect a fault somewhere else.  I just pulled out the manual, and I
>
> > would start by lifting the connection on E7, and connecting a 10MHz
>
> > xtal in series with a 10pF cap between the E7 pin and ground.  This
>
> > will bypass both the xtal and the frequency adjustment circuit.  If
>
> > that doesn't work, then the oscillator circuit is the problem - if it
>
> > does work, then remove the 10 pF cap and connect the xtal directly
>
> > between E7 and E8 - if it still works, it's almost certainly a bad
>
> > xtal.  If it worked with the 10 pF cap but not with the E8 connection,
>
> > then check the control voltage (E9: 0.5V-17V) - if that looks good,
>
> > then suspect the frequency control circuit.  If it's bad, then try
>
> > hooking it to +5V to verify the oscillator and then troubleshoot the
>
> > servo board.
>
> >
>
> > Regards,
>
> >
>
> > Pete
>
> >
>
> >
>
> > On Wed, Dec 21, 2011 at 5:00 AM, Azelio Boriani
>
> > <azelio.boriani at screen.it>  wrote:
>
> >> 10MHz crystals used in OCXO are designed for the temperature of the oven
> so it is not possible to find an off-the-shelf suitable crystal. Better
> find
> a crystal coming from an OCXO.
>
> >>
>
> >> On Tue, Dec 20, 2011 at 7:10 PM, Peter Bell<bell.peter at gmail.com>
>  wrote:
>
> >>> Hi, Don
>
> >>>
>
> >>> It's been quite a while since I worked on a FRK, but from what I
>
> >>> remember the only signals going to that oscillator board are power and
>
> >>> the control voltage. It might be worth checking the control voltage to
>
> >>> see if it's at a plausible value (nominal is 5V, spec range is 1V-16V,
>
> >>> IIRC) - if you have a spare xtal around, just try connecting it to the
>
> >>> pins on the PCB and see if it starts up.
>
> >>>
>
> >>> I'm not aware of the xtals being failure prone - I have seen one FRK
>
> >>> with a bad one, but having seen the condition of the system it was
>
> >>> removed from, that was clearly impact damage.
>
> >>>
>
> >>> Regards,
>
> >>>
>
> >>> Pete
>
> >>>
>
> >>>
>
> >>> On Wed, Dec 21, 2011 at 1:29 AM, Don Lewis<dlewis6767 at austin.rr.com>
>
> >>> wrote:
>
> >>>> A little help, pls, from the more experienced.  This is my first time
> into one of these .I have listened and learned from you' all for some time,
> though.  It can be intimidating in this close-packed FRK.
>
> >>>>
>
> >>>> I am trying to bring up an Efratom FRK  I have had for a while.  The
> 10
> MHz oscillator does not start upon power on.
>
> >>>>
>
> >>>> Any ideas where to look?
>
> >>>>
>
> >>>> I have done the following:
>
> >>>>
>
> >>>> *       I have it opened-up and applied 24vDC and the current starts
> up
> initially at 1.45 amp and slowly goes down to ~.6- .8 amps.
>
> >>>> *       Since I have no 10 MHz output, .so I looked at the oscillator
> board and nothing out from it.
>
> >>>> *       The 17 volt dc supply-rail is good, and the VCO input signal
> to
> the varacter control-circuitry is constantly ramping up and down slowly
> between ~1volt and ~15 volts.
>
> >>>> *       All the transistors in the oscillator circuit seem ok with a
> VOM,
>
> >>>> ..and when I purposely inject a 10Mhz signal into the collector of the
> 'oscillator' transistor (Q3), .I do get a clean 10Mhz out of the unit (of
> course it won't lock), .and I haven't even been into the rest of the unit.
>
> >>>> *       I think the crystal is bad, .I took the cover off the crystal
> oven, it 'looks' ok, . and the crystal heater in the oven is heating and
> regulating.
>
> >>>>
>
> >>>> Any ideas?  .does the 10 MHz crystal in these have a history of
> failing?  Can I get a replacement  crystal for it easily?
>
> >>>>
>
> >>>> How can I test this crystal for pass/fail?
>
> >>>>
>
> >>>> Thanks, .just my first test of the waters as a fledging time-nut.
>
> >>>>
>
> >>>> Don Lewis
>
> >>>>
>
> >>>> Austin, TX
>
>
>
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