Great thought on using the led. That goes in the bagOtricks. Regards Paul On Tue, Apr 24, 2012 at 9:29 AM, Ed Palmer <[email protected]> wrote:
> Joe, > > > On 4/24/2012 6:50 AM, J. L. Trantham wrote: > >> Ed, >> >> If it is, indeed, stable at exactly 5.000 000 000 MHz, it is probably >> locked. That being said, I would wonder if there is an indicator issue >> and >> perhaps a control logic issue. >> >> On the HP units, the AC Amplifier, that receives the signal from the Rb >> assembly, has been the source of some problems on my units. Also, the AC >> Amplifier sends a signal that indicates both a 137 Hz fundamental >> frequency >> being present and a 274 Hz 2nd harmonic signal being present to the >> control >> logic assembly as two of the 'required' signals to get a 'lock' >> indication. >> You might want to take the AC Amplifier out, put it on the bench and feed >> it >> a low level fundamental frequency, track that through the assembly then >> repeat with a 2nd harmonic signal and look at it's output. Same thing for >> the logic assembly to make sure that some of the 'required' signals are >> indeed present rather than 'failed on'. >> > > I did that. There were some bad solder joints in the amp / filter circuit > but otherwise, it was good. To test the entire signal chain, I replaced > the Rb lamp with an LED that was modulated at the fundamental (155 Hz in > this case) and then at the 2nd harmonic (310 Hz) and the signals appeared & > disappeared as expected. > > > I forgot to ask, did you find a manual? >> > > That was one of the reasons I bought this thing. It included the original > manual. There's also a partial manual online so I was able to familiarize > myself with the unit before I made my bid. > > > Ed > > Joe >> >> >> -----Original Message----- >> From: [email protected] >> [mailto:time-nuts-bounces@**febo.com<[email protected]>] >> On >> Behalf Of Ed Palmer >> Sent: Tuesday, April 24, 2012 12:55 AM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] Antique Rubidium Standard Questions >> >> >> Hi Joe, >> >> On 4/23/2012 9:45 PM, J. L. Trantham wrote: >> >>> Ed, >>> >>> I am not familiar with the Tracor units, only the 5061A and B as well >>> as the 5065A. These units use the 2nd Harmonic as an integral part of >>> the feedback loop. >>> >>> Without the 2nd Harmonic, is there another way to 'unambiguously >>> determine that it is locked', other than comparing it to a 'known', >>> 'locked' signal? >>> >> Strictly speaking, the answer is probably 'No'. After all, why would >> they include the 2nd harmonic circuitry if they didn't need it? There >> should be 2nd harmonic and I hope to find some somewhere. Remember that >> this unit is being brought back from the dead as a learning exercise so >> a few 'minor' issues aren't a show-stopper. The unit has been running >> for most of the day. I flipped the switch to open the loop. The >> frequency went from 5 MHz to 5MHz +0.045 Hz while the error meter went >> from 0 to -25 on a scale of 50. Close the loop and the frequency >> returned to 5.000 000 000 MHz and the error meter went back to zero. >> That certainly sounds like locking behaviour to me. >> >> I guess another way to ask the question is do you think you happen to >>> have a particularly good OCXO? >>> >> It's a 40 year old AT-crystal that hasn't had nearly enough recent run >> time to work the kinks out. I would be astonished to find that it's >> that good. But I realized that I've never looked at the oscillator by >> itself so I did a quick test. I measured an aging rate in the range of >> 0.2 ppm / day. If I cancel out all the aging, the results start to look >> like the earlier attachment. But not when it's unlocked. >> >> Ed >> >> >> Joe >>> >>> -----Original Message----- >>> From: [email protected] >>> [mailto:time-nuts-bounces@**febo.com<[email protected]> >>> ] >>> On Behalf Of Ed Palmer >>> Sent: Monday, April 23, 2012 10:17 PM >>> To: Discussion of precise time and frequency measurement >>> Subject: Re: [time-nuts] Antique Rubidium Standard Questions >>> >>> >>> Hi Joe, >>> >>> On this unit (not sure about others), the 2nd harmonic is used to >>> unambiguously determine that it is locked. But the 2nd harmonic has >>> no part in the acquisition or maintenance of the lock. That is done >>> by the fundamental. I can tune through resonance and see the standard >>> curve like fig. 5-7 in the HP 5065A manual (see attachment) except >>> mine doesn't quite make it to the full-scale saturation level. I then >>> tune to the resonance point and flip a switch to close the loop. It >>> doesn't turn on the nice green light because that's done by the 2nd >>> harmonic. But it also doesn't drift like an OCXO. Take a look at the >>> second attachment for an ~10 hour data run. The relatively poor >>> performance below 1000 seconds is due to my measurement setup. I was >>> looking for high Tau performance, not low Tau. >>> >>> Ed >>> >>> >>> On 4/23/2012 7:58 PM, J. L. Trantham wrote: >>> >>>> I don't understand how it can 'lock' without a 2nd Harmonic Signal. >>>> >>>> Joe >>>> >>>> -----Original Message----- >>>> From: [email protected] >>>> [mailto:time-nuts-bounces@**febo.com<[email protected]> >>>> ] >>>> On Behalf Of Ed Palmer >>>> Sent: Monday, April 23, 2012 12:54 AM >>>> To: Time-Nuts >>>> Subject: [time-nuts] Antique Rubidium Standard Questions >>>> >>>> I'm playing with a Tracor 304-B Rubidium Standard from 1969. I'm >>>> using it as a learning exercise to find out more about the guts of a >>>> Rubidium standard and how it works. >>>> >>>> This thing is a beast! Rack-mount, 3U high, 39 pounds (~18 kilos), 9 >>>> plug in circuit boards. The OCXO is an oddball frequency that is >>>> multiplied directly to 6.8 GHz. There's no synthesizer in that >>>> chain. A synthesizer is used to convert the oddball frequency to a 5 >>>> MHz output. >>>> >>>> It's sort of working. The error signal isn't up to spec, but it's >>>> strong enough to give a stable lock although there's no trace of a >>>> second harmonic signal. Allan Deviation is in the Xe-12 range from >>>> 1K to 10K seconds. The OCXO has a not-yet-resolved issue that is >>>> probably degrading the results. >>>> >>>> The lock frequency suggests that the Rubidium cell has drifted down >>>> by ~30ppt over the 40+ years since it was built. Is that reasonable? >>>> That's much more drift than the specification states, but I doubt if >>>> the spec was intended to be valid for 40 years! >>>> >>>> Could the drift be at least partially responsible for the lack of >>>> second harmonic? A message on the list ( >>>> http://www.febo.com/pipermail/**time-nuts/2006-April/020562.**html<http://www.febo.com/pipermail/time-nuts/2006-April/020562.html>) >>>> said >>>> that you could peak the second harmonic by adjusting the cavity >>>> tuning. If the cell and the cavity are out of sync would that kill >>>> the second harmonic? How close to they have to be? If this thing >>>> has a cavity tuning adjustment I haven't found it. >>>> >>>> FYI, I checked my counter (Racal 1992 referenced to an Efratom FRK-H >>>> Rubidium) against my Z3801A and Tbolt. Both measure 10.000 000 000 >>>> MHz. so I'm confident that my numbers are good. >>>> >>>> Thanks, >>>> >>>> Ed >>>> >>>> > ______________________________**_________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
