Using Garmin GPS 17HVS NMEA with RL70C

[Tigray]

Chuck, thanks for the info.
Connecting the GPS17 directly doesn't work. The Northsar NMEA output swings 0-5V, this works on the RL70 NMEA input. So I decided to develop an interface circuit to translate the -5V to +5V signal from the GPS17 to 0 - 5V. I used an old CMOS logic IC, a CD4009 hex inverter to do the job. I applied 5V (from a cigarette lighter USB cellphone charger power adapter) to VCC and VDD, Ground to VSS, the GPS17 output in series with a 10K resistor to one inverter input, that inverter output to another inverter input, then the second inverter output goes to the RL70 NMEA input. Also tie the other four inverter inputs to VSS. The input diodes on the CD4009 work with the 10K resistor to clamp the -5V/+5V signal to 0/5V so the output of the second inverter is a 0 to 5V swing in phase with the GPS17 output. This works nicely. Probably any 5V supply CMOS logic chip providing inverters or buffers will work if you can't find the old CD4000 or 74HC chips. I do see 74HC chips on Ebay and Amazon.
Thanks for the tip on only having one source for GPS data input into the Raymarine units, I will install a separate power switch for the GPS17 so I can have it active only when the Northstar is inactive.