Hi
A lot of commercial designs run through multiple lock strategies as they warm
up and
stabilize. What the ultimate lock approach is after they have messed around
very much
depends on what the customer is looking for. There are indeed FLL GPSDO’s in
some
very fancy systems.
PLL is the
Hi Bob
RRR.
In fact all my original GPSDOs in the '90s were FLLs, for radio comms
gear, essentially frequency counters with the error driving a PI loop.
They were controlling standard XOs. For new engineers, if they want a
project to teach them many skills, I recommend a GPSDO project from
Hi
In a GPSDO, an FLL can be done with no “cycle slips” between readings. In that
case, the I term will indeed
correct for long term errors. The net result will be effectively the same as a
PLL for long term error. That is by
no means to say that *all* FLL’s are done this way. Only that it is
Leo is right
Depends on the application. Phase lock for 1pps to trigger say,
simultaneous capture of many radio telescopes around the globe is a good
need for phase lock to a source. Frequency lock might suit many . change
of phase between two sources might indicate frequency change, or duty
Hi Dana,
I am just saying that, properly implemented, PLL and FLL are indistinguishable
as long as output signal is concerned while lock is present and that the phase
slew at regaining lock in PLL loop is counterproductive for one but necessary
evil for others. I have a feeling that FLL is
Hi
Welll … ummm ….. e ….
With things like time re-synch going on, the only thing you should drive a
clock with
is the PPS output. You can go on pretty much forever and ever with a FLL and
still have
a good PPS out.
Bob
> On Jun 23, 2019, at 10:44 PM, Hal Murray wrote:
>
>
>
t...@leapsecond.com said:
> Can you explain more what you use a GPSDO for? For most people a GPSDO is
> merely a replacement for a stand-alone XO or TCXO or OCXO or even rubidium.
> As such, the more stable and accurate the frequency the better. Which is why
> a FLL-based GPSDO, as Leo
Hi Dana,
Can you explain more what you use a GPSDO for? For most people a GPSDO
is merely a replacement for a stand-alone XO or TCXO or OCXO or even
rubidium. As such, the more stable and accurate the frequency the
better. Which is why a FLL-based GPSDO, as Leo describes, is a perfectly
fine
Hi
A lot depends on just how long your “frequency” samples are. If the GPS is good
to
a nanosecond, you are at 1x10^-11 at 100 seconds. It’s a rare crystal based
GPSDO
that will hold closer than that frequency wise.
The FLL is non peaking so that’s going to help things a bit as well.
Bob
>
Correction from Dana:
I meant "... without accumulation of phase error during normal times ...".
Sorry about that.
Dana
On Sun, Jun 23, 2019 at 11:45 AM Dana Whitlow wrote:
> Leo,
>
> Are you saying that you want to abandon phase lock altogether in favor of
> freq
> lock? Or just during
Hi Karl,
I will work on better website description. There are few loops in the device -
GPS reference is PLL and the synthesiser is now FLL (used to be PLL.)
Leo
> Hi, Leo. The web pages for your precision frequency references say they use
> PLL. Is that just for frequency generation, and
Leo,
Are you saying that you want to abandon phase lock altogether in favor of
freq
lock? Or just during the reacquisition following loss of and restoration
of the
reference?
By me definition of pure freq lock, there will generally be some permanent
(but varying)
frequency error, so that phase
Hi
On most commercial designs a “time reset” is done when coming out of holdover
to take
care of the PLL issue. This provision for this is detailed in most OEM specs.
If you watch
most of the eBay surplus GPSDO’s as they do their thing, you can see them do a
“hop”
when this happens.
Bob
> On
Hi, Leo. The web pages for your precision frequency references say they use
PLL. Is that just for frequency generation, and you use FLL for resyncing?
Karl
On Sun, Jun 23, 2019 at 7:01 AM -0700, "Leo Bodnar"
mailto:l...@leobodnar.com>> wrote:
I have to draw your attention to practical
I have to draw your attention to practical aspects of why some designs use FLL
rather than PLL.
Consider a GPS locked OCXO outputting GPS synced 10MHz signal.
Properly designed control loop will not produce much (if any) difference when
the reference (GPS signal) is present. In the end,
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