[time-nuts] PCB layout question for GPSDO

[Tobias Pluess]

Hi Tom

> This violates constraints as set out in the Ublox hardware integration manual.
how? I have read the hardware integration manual, and indeed, for the older modules (like LEA6 and so on) it does say "no traces under the module", but for the newer ones it doesnt explicitly say that. Is there some other manual I probably missed which discusses the PCB layout of the module in more detail?

> I would, but it can be dealt with.
:-) the voltage regulators can be easily exchanged with linear ones. Maybe I could do some phase noise measurements using switchers and also using linear regulators and then compare.

> - In some places your ground layer is severely broken up to reduce its effectiveness.
I have actually a 4 layer board (should have mentioned that), so the layer 2 is completely flooded with GND. On the bottom, I have just added some additional GND plane because there is enough space for it.

- Your antenna seems very close to the 1pps output and has traces underneath it
Yes, antenna is quite close to 1PPS :-/ is that a problem? the trace below the antenna signal is the 5 volt supply line for the active antenna and the 1PPS driver. 


Tobias
HB9FSX


________________________________________
From: time-nuts [time-nuts-bounces at lists.febo.com] on behalf of tom burkart [tom at aussec.com]
Sent: Thursday, January 30, 2020 23:55
To: time-nuts at lists.febo.com
Subject: Re: [time-nuts] PCB layout question for GPSDO

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



_______________________________________________
time-nuts mailing list -- time-nuts at lists.febo.com
To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.