[time-nuts] PCB layout question for GPSDO

[Mike Ingle]

Hi Tobias,

I agree with Tom, that I also like PTC fuses, but don't forget that they
have a sometimes significant IT drop.  Been there, been burned.

--mike


On Fri, Jan 31, 2020 at 3:36 AM tom burkart <tom at aussec.com> wrote:

> Hi Tobias,
> additional answers below:
>
> Quoting Tobias Pluess <tobias.pluess at xwmail.ch>:
>
> > a) is it acceptable to route some signals under the GPS module? As
> > one can see, the signals I have routed under the GPS module go to
> > the front panel interface, i.e. they are not highspeed signals or
> > so, but I still wonder whether you experts would worry about it
> > (like "oh no, routing anything near the GPS module will disturb it
> > and decreases its sensitivity" or something).
> This violates constraints as set out in the Ublox hardware integration
> manual.
>
> > b) would you worry about the switching regulators? I know linear
> > would be better, but the professional GPSDOs also have switchers,
> > and besides that a linear regulator would not be so nice because my
> > power supply will be at least 15 volts.
> I would, but it can be dealt with.
>
> > c) is the usage of a RS232 chip a good idea or would you kick that
> > out because they produce such massive amounts of EMI that it will
> > disturb my GPS module or OCXO?
> Keeping it away from sensitive circuits will probably suffice.
>
> > d) is it a wise idea to use an LC filter for the OCXO power supply,
> > or does this lead to another rabbit hole because the inductors will
> > pick up magnetic fields (50 Hz...) and modulate the OCXO?
> All depends whether you will bath the whole thing in 50Hz stray
> magnetic fields. ;-)
>
> > e) anything else important I forgot?
> - Please double check your wiring of the GPS module it looks back to front.
> - In some places your ground layer is severely broken up to reduce its
> effectiveness.
> - Your antenna seems very close to the 1pps output and has traces
> underneath it
> - I quite like resettable PTC fuses (no need to replace)
>
> Tom
>
>
>
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