The Eagle ELC-1 and Lowrance LC-1 loran antenna coupler modules each have a
4 pin plug at the end of the long pigtail cable.

Their pinout for the 4 pin plug is:

1 ground
2 XMIT
3 12vdc+
4 recv

Ground I understand. 12vdc+ I understand. RECV I understand. What I
don't understand is XMIT. What function does this wire play ? What would
be transmitted from a loran set?

I assume pins 3 and 4 would be jumped together and go to the center of the
chassis bnc fitting on most loran sets. Pin 1 would be hooked to chassis
ground. All this sound right?

That leaves pin 2. Does it just float?