gta02-core and external GPS antenna

Werner Almesberger werner at
Thu May 28 21:53:13 CEST 2009

There's one simplification that looks attractive to make in gta02-core
and that's to remove the external GPS antenna connector. From what I've
heard, this antenna is rarely used in the FreeRunner, and for
stationary use, one could connect an external antenna to the socket for
the internal antenna.

There are the following benefits in removing the external antenna:

- reduced SMT cost by removing about a dozen components, some of them
  unique. Due to its shape, The antenna connector may also need
  special treatment in SMT, such as glueing.

- fewer components means less risk of getting interferences. This goes
  particularly for the external antenna socket when open.

- simplifies the layout of the GPS RF circuit and thus reduces the
  risk of us getting something wrong.

- when investigating the SD/MMC vs. GPS problem, Andy found that the
  antenna selection circuit is operating with an incorrect voltage.
  Apparently, this didn't cause any observable problems, but then
  you never know what's really behind the occasional glitch ...

- in case future designs are made based on gta02-core, a smaller GPS
  subsystem may allow for a smaller PCB size or give more room to
  other subsystems

There are also a few disadvantages:

- if you really need the external GPS antenna along with the internal
  one, this will not be a welcome change

- the antenna connector also helps to hold the PCB in place. Without
  it, there is only USB on that side of the board to assist the
  snap-in mechanism. (Probably doesn't matter all that much, though.)

- removing the connector leaves an empty hole in the case

I think the benefits outweigh the disadvantages, so I'd like to see
the external GPS connector gone.

Any thoughts ?

- Werner

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