Nice module, but I really need a USB connection for the present design. However, there seem to be a number of GPS modules on eBay at your link, Since the GPS unit's only requirements are that it be within the Pi Zero form factor AND connect with USB, substitutes are straightforward and I will poke some more. Thanks!
What is the negative downside of the Adafruit GPS modules based on the MT3333 chipset compared to say the U-blox chip sets?
It is possible the foil is acting as a ground plane increasing sensitivity. However that does not then explain why it is highly sensitive in the open away from the assembly, and apparently desensed near the assembly.
But if you are correct and it is acting as a ground plane, then that is a two way street and it is also acting as a ground plane for the modules below and directing their noise away from the module. Either way: it does not work without it and works with it. I know for a fact from other testing that all the modules are very noisy electrically, the system is sensitive to this noise, and managing electrical noise in the configuration is critical for the design.
I have no plans to buy SIRF chips in the future: the present standard solution uses them and this is a replacement for the present design. And since the SIRF chip for this application is the default standard, if the new system is as good as or better than the SIRF chip, we are good to go. It is the present vendor has to deal with the shortage of SIRF chips.
Thanks for your comments and assistance!
And any further leads/comments on alternate chip sets for GPS modules within the PI Zero form factor AND using USB would be much appreciated!