[time-nuts] Nortel GPSDO osc age alarm

EB4APL eb4apl at cembreros.jazztel.es
Fri Jan 24 19:27:22 UTC 2014


Volker,

I have also a Trimble Nortel NTG550AA and fortunately it works very well 
from the beginning.  I have a downloaded manual and some other info that 
I can send you if interested.
And one word of caution: if you observe the cable that goes from the 
main board to the small interface board, you will see that one of the 
connectors is reversed so be careful if you make a custom one for your 
cabinet, do it in the same fashion.  Using a normal cable produces 
bizarre results that can actually drive you nuts, don't ask how I know.
The coax connector, J5 is a 9.8304 MHz output, an odd frequency used by 
the cell tower equipment, J4 carries 1/2 PPS (even seconds), the next 
one (J1) is the for the antenna and J4 is the 10 MHz output. You already 
know that but I want to note that the 9.8304 frequency has mislead some 
users to think that it was the 10 MHz output, not your case.

The seller (Bob Mokia , fluke.l) is well known to the Time Nuts, he has 
a technical background and normally known quite well what he sells and 
is very positive about solving the problems that may arise, his only 
problem is that his English is worse than mine .  I think that he 
regularly monitors this list.

I have observed a strange thing on this offering, at the end of the page 
he says:

"power on it ...

after 30 minutes/it will locked/10mhz come on the SMB connector

1pps on the back d sub connector "

I never heard of a 1PPS signal on these units, only 1/2 PPS on the J4 
coax and I had asked on this list if anybody had found how to extract 1 
PPS from the unit.   I have to put a scope on the DSR pin because it is 
the only connected to the main board other than TxD and RxD.  Could you 
verify this on your unit when you change the OCXO and get it running?

Best regards,
Ignacio EB4APL


On 24/01/2014 16:23, Volker Esper wrote:
> ...thanks, Bob, it seems to be the oscillator, that is at it's limit, it
> cannot tune to 10 MHz at full EFC voltage, see new thread (started by Mark).
>
> Volker
>
> Am 24.01.2014 01:09, schrieb Bob Camp:
>> Hi
>>
>> That’s a cell phone base station board. It’s got a bunch of outputs, some of which are related to the cell network it was built for rather than 10MHz. I’d bet your 9.8 MHz output is one of those. They are DDS based so there likely is some range of possible outputs.
>>
>> The age alarm is not unusual on a newly powered up board. It’s moving faster than it should. It may settle down.
>>
>> The DAC at limit is not a real good sign ….
>>
>> Bob
>>
>> On Jan 23, 2014, at 6:43 PM, Volker Esper <ailer2 at t-online.de> wrote:
>>
>>> Hi!
>>>
>>> I bought a Trimble/Nortel GPSDO
>>>
>>> http://www.ebay.de/itm/300933951405?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.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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