It is possible to feed GPS into two ports at once.

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I once had to do this to prove a Kenwood PMR radio was not sending GPS coordinates correctly, for an AVL system, so we hooked up the GPS to the radio, and via a splitter to a laptop's serial port. We then compared what got captured on the laptop and what was sent by the radio, and sure it was eating up decimal places.

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So, what you need to do is to get the TX data pin from the GPS (it's either pin 2 or 3 on a DB9 connector, I forget which one now), and connect it to the RX pin on the two serial ports you want data into, and voilà.

Cheers,

Mother