I have a number of GPS etc. modules which I'm using for experimental purposes, with (genuine) Ublox neo-xx cans onboard. In general I select these to have provision for an external antenna, very often they support both an external and an onboard antenna.
I've seen various mutterings that a capacitor should be removed so that there is only a single RF source. Can anybody provide definitive or at least informed information on this?
In more detail, the attached photo shows part of a GPS module with SMA and IPEX connectors paralleled at the bottom and left, and the centre connection of the onboard (ceramic patch) antenna towards the top right.
The external antenna is connected to C8 and L1 in parallel, with C8 connected to U3 which is an unmarked six-pin device.
The internal antenna is connected to C4 and L2 in series, hence to U3.
The fragmentary instructions I've seen suggest that C8 should be removed if the external antenna is being used... which is of course rubbish since that's the in-path device. However the seller who advised that must have got the notion from somewhere.
If U3 is a passive combiner, e.g. from Mini-Circuits, then is is reasonable that an unused RF source should be isolated since an out-of-phase signal would mess things up.
If U3 is an active switch, e.g. from Peregrine as mentioned in
https://www.u-blox.com/sites/default/files/products/documents/GNSS-Antennas_AppNote_%28UBX-15030289%29.pdf , then it's not reasonable to expect to have to remove components.
I lean towards U3 being active, since the component layout on the module is approximately as described in the Ublox appnote- even if the open-circuit detection has been omitted or simplified. However I'd be interested in the community's opinion or experience.
MarkMLl