[time-nuts] Nortel GPSDO osc age alarm

GandalfG8 at aol.com GandalfG8 at aol.com
Fri Jan 24 17:50:45 EST 2014


In a message dated 24/01/2014 21:48:27 GMT Standard Time,  
ailer2 at t-online.de writes:

New ways  of RF design - see photo ;-)
-------------
 
Definitely the last word in high rise developments:-)
 
And glad to hear you got it sorted.
 
----------------



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
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