[time-nuts] PCB layout question for GPSDO

[Mike Ingle]

Hi Tobias,

IT drop should have been IR drop.  --mike

On Fri, Jan 31, 2020 at 7:14 AM Mike Ingle <finndmike62 at gmail.com> wrote:

> 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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>