I'm looking at some GPS modules linked below:

http://www.hoperf.com/upfile/GPS04.pdf

Please see pages 3 and 4.

The datasheet says it needs an active GPS antenna. It has three pins related to the external antenna:
Pin 17: Antenna In
Pin 19: V_ANT
Pin 20: VCC RF

I get that pin 17, antenna in, is actually the RF signal line.

What I don't understand is powering the active antenna. V_ANT is shown as an input for the active antenna's power -- as in connecting the circuit VCC to this pin. What I don't get is pin 20, "VCC RF." It says "voltage output for active antenna" in the datasheet. I almost take this to mean that it can be tapped in to to power the external active antenna, but when I look up active antennas on google I just see a single wire from the antenna -- and no voltage in.

What exactly is the difference in Pin 19 and 20 here?

Thanks!

 

One is the external input voltage for the antenna and one is the output RF

You may not require external voltage unless you are using a more powerful antenna.

 

One is the external input voltage for the antenna and one is the output RF

You may not require external voltage unless you are using a more powerful antenna.

Thanks for your quick reply. I'm about to seem REALLY silly now:

So, pin 17 is in fact antenna in, pin 19 is the input voltage pin for the active antenna........
But I just don't understand "output RF"

Why do I need "output RF." Isn't everything being processed internally once I feed the antenna to it?

 

There isn't an "RF Out". Only a voltage supply for an active external antenna. This IC is a GPS decoder that gives serial output data based on received data. It doesn't re-transmit the GPS signals (which is a touchy subject on it's own for US FCC compliance).

V_ANT and ANT_IN are both inputs. Only Vcc_RF is an output.