[time-nuts] unknown GPSDO
tshoppa at gmail.com
Tue Jul 18 11:39:24 EDT 2017
The original Brooks Shera unit was 20 years ago and is pretty well
documented in QST and his website. In the original the loop filter
timeconstant was set by jumpers or DIPswitches. And I think the EFC gain
factor was set somewhere else (DIPswitch? Resistor network? Both?)
Shera's webpage documents some improvements and changes up through 2001 but
there have been an incredible number of variations out there in the wild as
folks move parameters that used to be set in hardware/DIPswitches to
firmware with LCD config screens etc. I think the OP's unit shows a decade
or more of evolution past what Shera documents.
Is there a "Brooks Shera GPS family tree" out there showing recent
evolution of the design?
On Tue, Jul 18, 2017 at 11:10 AM, David C. Partridge <
david.partridge at perdrix.co.uk> wrote:
> ISTR that you started it with a short time constant to get locked, and
> once you had lock you would increase the time constant in a few steps to a
> final value of (say) 1000s or so.
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Volker
> Sent: 18 July 2017 14:15
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] unknown GPSDO
> Thanks so far. I will have a look at the docs.
> The machine is running well, particularly the OCXO is performing very good
> when free running (without GPS signal). It is stable and its ADEV looks
> good (2E-10 at 10s). Not so the overall ADEV (when GPS locked)
> (1E-5 at 10s). It seems to not having the right filter time constant what
> had to be much longer. As I understand the documents, the filter constant
> can be programmed and I will experiment whith that this afternoon.
> Thank you
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