[time-nuts] Nortel GPSDO osc age alarm
Volker Esper
ailer2 at t-online.de
Fri Jan 24 21:31:58 UTC 2014
New ways of RF design - see photo ;-)
Ok, I put three 1N4148 in series between DAC out and EFC in and a pull
up of 4k7 up to 12V. It shifts the DAC voltage 1.8 volts up, so the osc
is able to tune to 10MHz+3Hz. Locked!
Now I can go back to the sofa, having a beer or two, being sweet again
to my wife and my dog, :-)
Thanks
Volker
Am 24.01.2014 17:49, schrieb Volker Esper:
> Thanks so much, Nigel, for this very interesting mail.
>
> Yes, the voltages are exactly as my ones. And yes, I've removed the
> oscillator, already. I then removed the thermal isolation from the osc,
> as well as the label, in slight hope for a hidden tuning screw. Of
> course, there isn't any.
>
> I, too, had this idea to level shift the EFC voltage. So I took seat at
> my computer to find out, which maximum EFC voltage would be ok. And saw
> your mail. Do you have any further information about the osc? The number
> on the sign (Trimble *0110-2450-T* *34310-T*) isn't really informative.
> By the way: When removing the big Trimble label I found a smaller one
> beneath, reading "DOC2127 0101/1940"; I think it's a Tekelc osc?
>
> Is there a pull-up resistor behind the EFC input pin so that I could use
> two diodes for level shifting? Or how did you?
>
> This part is more thrilling than I expected...
>
> Regards
>
> Volker
>
>
> Am 24.01.2014 12:08, schrieb GandalfG8 at aol.com:
>> Hi Volker
>>
>> One possibility, as I found with one of these recently, is that your
>> oscillator has aged such that the required EFC voltage for 10MHz output is now
>> outside the range provided by the board.
>>
>> The EFC behaviour can be tracked if Lady Heather is enabled from switch on
>> and the DAC voltage monitored.
>>
>> The EFC voltage should start at 3 volts, in my case reported by LH as
>> 3.000002 Volts, and will sit at this level until enough satellites are being
>> tracked for the board to decide it can start the conditioning process, at
>> which point the DAC voltage will ramp upwards over the course of a few seconds
>> until the point is reached where the oscillator frequency crosses 10MHz and
>> the control loop takes over.
>>
>> All standard stuff of course but, as you've discovered, if the oscillator
>> hasn't reached 10MHz by the time the EFC voltage reaches, in my case
>> anyway, approximately 5.6 volts the board's "OSC" report switches to "BAD" and
>> "Normal OSC age" switches to "OSC age alarm" and LH highlights both in red.
>> The EFC voltage finishes its ramp at 6 Volts, reported as 6.000004 Volts,
>> and then just sits there, all exactly as you're seeing.
>>
>> Having removed my "faulty" oscillator, something that needs to be done
>> VERY carefully to avoid damage to the board, I found that it required an EFC
>> voltage of just under 6.6 Volts for the the output frequency to reach 10MHz.
>>
>> The seller, fluke.l, was very helpful as always and offered to supply a
>> replacement 34310-T oscillator, this one did have it's required EFC voltage
>> in the correct range and resolved the problem.
>>
>> However, whilst waiting for the replacement to arrive I left the original
>> oscillator on test and monitoring it for a while suggested that the only
>> thing "wrong" with it was the required EFC voltage, so I reconnected it to
>> the board using a wired lash-up on the bench with a simple 2 Volt level
>> shifter inserted into the control loop and did indeed get a locked condition
>> with Lady H reporting the DAC voltage from the board as close to 4.5 volts.
>>
>> This suggests that whilst the board design requires the oscillator EFC
>> Voltage at 10 MHz to be between 3 and 6 Volts an oscillator that falls outside
>> this range shouldn't automaticall be assumed to be "faulty" in more
>> general terms, although it's obviously getting a bit long in the tooth and that
>> doesn't help much if it happens to be soldered into your circuit board !
>>
>> Whilst it is possible to remove and replace the original oscillator there
>> is an alternative to physical replacement, one which I've now implemented,
>> and this uses the mounting positions already available beneath the
>> oscillator, not usable though until it's removed, to fit a couple of SMA or SMB
>> connectors.
>> These two connectors couple the 10MHz signal from the oscillator into the
>> board (J9) and the EFC Voltage out to the oscillator (J10).
>> Although there is a regulated supply available from the oscillator, which
>> might be expected to supply the EFC circuitry, in practice this connection
>> does not seem to be required.
>> I have not investigated further as yet to determine whether the board auto
>> senses and uses this supply if it is present, or whether it always just
>> ignores it, but it doesn't seem to be an issue either way and it's interesting
>> to note, at the extremes anyway, that LH does report the DAC voltage to be
>> the same in both instances.
>> The oscillator can be powered from the board or given its own supply, in
>> which case the only required connections between them are the two coax leads.
>>
>> Using this arrangement, and some variation of a positive or negative level
>> shifter if required, it becomes possible to use different oscillators with
>> the Nortel board and it does become an even more interesting toy.
>>
>> One limitation though when using the Nortel boards in this way is that
>> they don't seem to share the versatility of the Thunderbolt when it comes to
>> modifying the oscillator conditioning parameters.
>> It's suggested in the LH documentation that such commands are currently
>> "undocumented" but that also leaves the possibility that any such change
>> might only be a firmware option.
>> If anyone has further information on this that would be much appreciated.
>>
>> I've been sufficiently impressed with the modified unit that I'm seriously
>> considering modifying another one, even though it doesn't actually "need"
>> it, although not over enthusiastic about repeating the oscillator removal.
>> However, an added bonus with this configuration is that it's also more
>> forgiving when it comes to any damage caused during removal of the original
>> oscillator, since the pads for the external connectors are separate from the
>> internal oscillator pads. Obviously it needs to be ensured that any
>> necessary continuity is maintained but that could be easier if a board mounted
>> oscillator is no longer required.
>>
>> The later single board unit, the NTBW50AA, has a similar external connector
>> arrangement but in this case the connector pads are available without
>> removing the original oscillator.
>> This hints at the possibility that perhaps a simple track interruption
>> might allow fitting of an external oscillator with the original still onboard
>> but examination suggests that the onboard connections route first to the
>> internal oscillator so that would probably still need to be removed.
>>
>> Regards
>>
>> Nigel
>> GM8PZR
>>
>>
>>
>>
>>
>> In a message dated 23/01/2014 23:59:34 GMT Standard Time,
>> ailer2 at t-online.de writes:
>>
>> Hi!
>>
>> I bought a Trimble/Nortel GPSDO
>>
>> http://www.ebay.de/itm/300933951405?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m
>> 1497.l2648
>>
>> and Lady Heather's now tells me that everything is alright - except
>> - DAC 6.000004V
>> - OSC BAD
>> - osc age alarm
>>
>> The rectangle "10MHz" output signal (J5) shows a signal at about 9.8MHz
>> (a deviation of about 200kHz), wobbling 4Hz up and down. Oddly enough,
>> the direct oscillator output (J4) shows a sine wave at a stable
>> 10.0000004MHz (a deviation of 0.4Hz).
>>
>> It seems to me it's not the oscillator that is bad but the servo loop -
>> what can I do?
>>
>> Thank you
>>
>> Volker
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DF9PL_GPSDO3_DSCF3003_bb.jpg
Type: image/jpeg
Size: 58015 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20140124/fd9eb0bb/attachment.jpg>
More information about the Time-nuts_lists.febo.com
mailing list