[time-nuts] Lucent KS-24361, curious observation

Bob Camp kb8tq at n1k.org
Mon Dec 1 20:27:32 EST 2014


Hi

> On Dec 1, 2014, at 7:17 PM, Doug Ronald <doug at dougronald.com> wrote:
> 
> Bob, thanks for the answers.
> 
> I am guessing my Garmin active antenna isn't drawing enough current, or is on the hairy edge. I won't worry about the occasional flashing LED.

If it gets to the point it bothers you, a resistor on a power splitter will take care of the problem. It’s probably worth fixing, the unit may go into holdover each time it thinks the GPS has gone away.

> 
> My concern with the 1 PPS locking the 5 MHz oscillator isn't with the quality of the 1 PPS, but that there is only one update every 5,000,000 cycles of the oscillator. It seems like that infrequent an update would cause jitter. 

The time constant of the loop that locks the OCXO to the GPS is probably in the 500 to 5,000 second range. The GPS signal has a lot of jitter on it, so filtering needs to be pretty slow. There is a bunch of stuff in the archives about all of the how and why of this.

Bob

> Maybe because the oscillator is of such high quality, it doesn't need more periodic updates.
> 
> Thanks,
> -Doug
> 
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
> Sent: Monday, December 01, 2014 3:50 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Lucent KS-24361, curious observation
> Importance: Low
> 
> Hi
>> On Dec 1, 2014, at 4:20 PM, Doug Ronald <doug at dougronald.com> wrote:
>> 
>> I have also received mine, and powered them with my GPS antenna indoors. After a 20 minute wait, I had full lock, and proceeded to compare the 15 MHz to WWVB. I saw a 20 degree shift in 4 hours which was pretty linear. I don't know if that is WWVB's propagation variation, or the Lucent "warming-up", but I'm a happy camper as I have never had a decent reference here before. I have not yet tapped into the diagnostic information available on the "Diagnostic" port.
>> 
>> I have a couple questions which someone may have an answer for:
>> 1) Every once-in-a-while, REF-1's "NO GPS" LED will flash. It flashes twice, three times, or four times, then back to extinguished for a long time. Anyone also see that on theirs, and what might the unit be trying to tell me?
> 
> If the light flashes, that’s saying the antenna current is over / under the limit the box is looking for. 
> 
>> 2) What is the 5 MHz crystal oscillator locked to? If it the L1 or L2 carrier - cool, or the PRN code clock - okay, but if it is the 1 PPS - ugh. Since the sync signal must go through the jumper cable, I suspect it is the 1 PPS. 
> 
> The 1 pps out of the GPS module is what they lock to . There is a lot of information in the archives explicating why Doppler on L1 or L2 make direct carrier lock less useful. 
> 
>> Anyone know, and if it is the 1 PPS, is that as ugly as I believe?
> 
> The PPS is s differential output. Run into a proper receiver it looks pretty good to me.
> 
> Bob
> 
>> 
>> -Doug Ronald
>> 
>> -----Original Message-----
>> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Paul
>> Sent: Monday, December 01, 2014 8:48 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Lucent KS-24361, curious observation
>> 
>> On Mon, Dec 1, 2014 at 11:15 AM, Graham <planophore at aei.ca> wrote:
>> 
>>> It has been less than 18 hours since I powered them up so I am not 
>>> yet wondering why the the REF-0 LED's are in the state they are as I 
>>> have seen reports of others having to wait 24 hours or so before every "locks in".
>> 
>> 
>> 
>> There are differing states.  My pair went OK+Standby in about 10 minutes but they're not "stable" at that point.
>> 
>> Here's a log snippet:
>> 
>> Log 019:20141128.00:00:00:  Power on
>> Log 020:20141128.00:00:26:  Power settings ok, Int: 17 dBm, Ext: 17 
>> dBm Log 021:20141128.00:52:21:  Position hold mode started Log 
>> 022:20141128.01:28:32:  GPS reference valid at 20141128.20:34:00 Log 
>> 023:20141128.20:35:04:  Locked mode entered Log 024:20141129.10:35:03:  
>> Ready for 4 hour flywheel Log 025:20141129.16:35:03:  Ready for 8 hour 
>> flywheel
>> 
>> 
>> The first timestamp after power-on is 00:00 of the last valid date prior to power-off.  I assume the deltas are correct.  So 1:29 to Locked and 20 more hours to "stable".  Holdover uncertainty continues to decrease for many more hours.  It decreased from hundreds of microseconds to 3 at the time of that log and is now at  900 nanoseconds.
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