Are external GPS antennas interchangeable? I realize that the connections will be different, but aren't the antennas themselves basically the same same thing regardless of make and model? The reason I'm asking is because I have aquired an antenna that is not meant for my unit. If I can find a way to connect it will it work?

What unit and what antenna? Lowrance makes an adapter(I have an extra) to use several antennas for several different units. You can't use a humminbird on a Lowrance though(Well if your savy enough you can make anything fit everything if you try I guess).

You can't use a humminbird on a Lowrance though(Well if your savy enough you can make anything fit everything if you try I guess).

This is what I'm trying to do. It's a Lowrance unit and an antenna of unknown origin. I just don't know if I would be wasting my time trying to rig a connection. 

If it's a Lowrance it is about 4-5" across, round with a flat bottom. Top is shaped like a petri dish turned upside down. go to the Lowrance site and you can eyeball one. BPS list them with pics also.

Based on what I've seen at the connectors, GPS antennas are both active and passive,  meaning that they must receive signals from the satellites and then pass this info to the head unit.  They would necessarily, require a 12 volt source, plus the wiring to communicate with the head unit.  I have no idea if the connector wiring from the antenna to the head unit has been standardized across all manufacturers.  I would think not, but it's just speculation on my part.