[time-nuts] Why is holdover LED on HP 58503A not lit, when GPS lock is unlit too?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 18 December 2016 at 14:31, Tim Shoppa <tshoppa at gmail.com> wrote:

> A common misconception, is that holdover is the opposite of GPS lock.
> Sometimes we might even talk about the two as if we're in one or the other.
> But really the power-on state, is that we're in neither holdover or GPS
> lock.
>
> Holdover means the smartclock previously had GPS lock and had used it to
> characterize the aging of the OCXO, and is maintaining the EFC
> extrapolation, such that it believes it can still produce accurate time and
> frequency through the GPS loss.
>
> The state of your clock at the moment, is that it has never had GPS lock
> since regaining power, it does not know what time it is, and it has not
> characterized or extrapolated the aging of the OCXO. So it is definitely
> not in holdover.
>
> Tim N3QE
>

Cheers Tim, that makes sense.

I'm a bit concerned it has not managed to track a single satellite, despite
it has been on 5 hours or so. But perhaps things have improved, as its not
attempting to track 6 (PRN=15, 2, 21, 25, 26 and 28), whereas before it was
attempting to track just with a PRN of 32. I'm hoping its current status
(see below), is looking more hopeful than what it was before.

scpi >
scpi > SYSTEM:STATUS?
------------------------------- Receiver Status
-------------------------------

SYNCHRONIZATION ........................................... [ Outputs
Invalid ]
SmartClock Mode ___________________________   Reference Outputs
_______________
   Locked                                     TFOM     9
FFOM     3
   Recovery                                   1PPS TI  --
   Holdover                                   HOLD THR 1.000 us
>> Power-up: GPS acquisition                  Holdover Uncertainty
____________
                                              Predict  --

ACQUISITION .............................................. [ GPS 1PPS
Invalid ]
Tracking: 0 ____   Not Tracking: 6 ________   Time _____ +1 leap second
pending
                   PRN  El  Az                UTC      14:43:22 [?] 01 Jan
1998
                   *15  -- ---                GPS 1PPS Invalid: not tracking
                   *20  -- ---                ANT DLY  0 ns
                   *21  -- ---                Position
________________________
                   *25  -- ---                MODE     Survey:      0%
complete
                   *26  -- ---                         Suspended: track <4
sats
                   *28  -- ---                INIT LAT N  51:39:03.825
                                              INIT LON E   0:46:36.278
ELEV MASK 10 deg   *attempting to track       INIT HGT          -14.04 m
(MSL)
HEALTH MONITOR ......................................................... [
OK ]
Self Test: OK    Int Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
OK
scpi > SYSTEM:STATUS?
------------------------------- Receiver Status
-------------------------------

SYNCHRONIZATION ........................................... [ Outputs
Invalid ]
SmartClock Mode ___________________________   Reference Outputs
_______________
   Locked                                     TFOM     9
FFOM     3
   Recovery                                   1PPS TI  --
   Holdover                                   HOLD THR 1.000 us
>> Power-up: GPS acquisition                  Holdover Uncertainty
____________
                                              Predict  --

ACQUISITION .............................................. [ GPS 1PPS
Invalid ]
Tracking: 0 ____   Not Tracking: 6 ________   Time _____ +1 leap second
pending
                   PRN  El  Az                UTC      16:59:08 [?] 01 Jan
1998
                   * 8  -- ---                GPS 1PPS Invalid: not tracking
                   *10  -- ---                ANT DLY  0 ns
                   *11  -- ---                Position
________________________
                   *12  -- ---                MODE     Survey:      0%
complete
                   *13  -- ---                         Suspended: track <4
sats
                   *30  -- ---                INIT LAT N  51:39:03.825
                                              INIT LON E   0:46:36.278
ELEV MASK 10 deg   *attempting to track       INIT HGT          -14.04 m
(MSL)
HEALTH MONITOR ......................................................... [
OK ]
Self Test: OK    Int Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv:
OK