[time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
jack at hudler.org
Wed Dec 13 19:59:51 EST 2006
If I'm totally missing something here please correct and enlighten me.
On the subject of Brooks Shera's design, the one thing that troubles me is the
use of a 24 MHz oscillator to count the width of the 1PPS signal.
This yields a precision of 4.16e-8, but does it really?
This oscillator is uncontrolled and any drift would exist as noise that would
have to be filtered (He uses a software low pass filter).
Question: Why not multiply the VCXO or OCXO output by 5 or 10 and run that into
24 or 32 bit counter? OR just sample the counter on every 10th PPS?
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf
Of Richard H McCorkle
Sent: Wednesday, December 13, 2006 4:44 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
I would contact Brooks Shera directly before you go any further as the span
of his controller is set at 4.5e-8 and the maximum span on an LPRO is about
5e-9. He can reprogram the controller by changing the filter gain and loop
time so it is about 8X more sensitive so it will work with a direct
connection to the LPRO. I have a controller modified with the filter gain is
scaled up 1 step and the loop time set to 120 seconds and this works well
with an LPRO attached directly to the DAC.
----- Original Message -----
From: "Brendan Minish" <ei6iz.brendan at gmail.com>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Wednesday, December 13, 2006 9:13 AM
Subject: [time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
> Hi I am looking for info on using the Brooks Shera GPS-VCXO Controller
> with an EFRATOM LPRO-101?
> I currently have it locking an old and unknown single oven Xtal
> oscillator this is working as well but I hope to replace this with the
> Has anyone any suggestions as to how best to choose the correct values
> of R5 and R6 for use with the LPRO-101 C field control input.
> Brendan EI6IZ
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