that device is a commercial marine solution - no doubt ruggedised and the outputs are optically isolated meaning its pretty rugged - [good in a marine situation].

For your use however, you're probably planning on building a homebrew solution/interface to your GPS and you presumably need to convert the GPS signals from TTL level to "RS232" level already.

This means you may already have most of the solution required to do this now.

I would probably change the existing MAX23X circuit design you have to feed the GPS NMEA (TTL Level) signal out to multiple of the TTL level inputs on [presumably] your MAX232 or 233 chip instead of just the one input as now.

I can't recall exactly which one, but one of the MAX2XX chips has 4 TTL inputs and hence 4 RS232 outputs "on board", so you could have 4 independant, short circuit protected serial lines from the one GPS with a little solder work and some additional wiring.

The MAX232 may not have enough TTL level inputs - its has 3 TTL outputs and 2 inputs I think [ but - I may be wrong and have it the other way way round].

In that case, two MAX chips may be required, simply wire them to power, ground, and seperate capacitors (if required) up the same way. then wire the circuit so that the TTL level output signal from the GPS goes to the first MAX chips pair of TTL level inputs in parallel, then do the same for the second MAX232 chips TTL inputs from the same GPs TTL input.

Of course two MAX chips like this doubles your power requirements, but in the wider schema of things, thats probably ok.

If you don't need the MAX chip in your GPS interface [because the GPS is already outputting RS232 levels], then a simple splice driving multiple serial ports might work - but it would depend on the loads imposed on the signal by the serial ports and the transceivers used in the GPS device itself (and possibly whether or not the GPS was running on batteries or not) as to how sucessful it was.

If it did not work and you already had RS232 level outputs you wanted to feed to multiple devices, you could have a small "black box" device that used a MAX23X chip that took the RS232 level signal from the GPS in, [to convert it to TTL], then send it out again via the TTL level inputs to the on chip TTL level outputs, thus creating a "buffered splitter" device - the only requirement being that you can power this black box from 5 volts somehow - possibly from the GPS itself.
The power drain won't be enourmous - probably 10-20 millamps.

You could potentially power this from a [one or other] of the serial ports you're pluggingthe outputs into by putting a small 7805 "low power" voltage regulator and some zener diodes to derive the 5 volts need to run the MAX chip(s) from your pc's serial port (connected to the RTS and DTR signals) - or even just using 4 AA cells will do - provided you have a manual on/off switch or the batteries will go flat over time.

You could use this balck box to get up to 3 serial ports out of the one serial output that way.

Also note, you may be able tomultiplex multiple "RS232 level" inputs (from your PCs transmit signals) (once converted to TTL by a MAX chip) to your GPS's serial TTL level input via a MAX23X chip and either a 7407 open collector hex buffer (or 2 circuits from a 7405 hex invertor) using a "weak" (e.g. 4k7) pullup to +5V. This would let anyone of the Pc's talk to the GPS, but only one at a time can "talk"

Folks who have been working with interfacing to ISO7816 compliant (i.e. smartcard) devices using their PC serial port will know this trick because its used to multiplex the PC's RS232 TX and RX signals on the single IO line on the smartcard.