GPS active antenna question

Discussion in 'The Projects Forum' started by wannaBinventor, Nov 27, 2010.

  1. wannaBinventor

    Thread Starter Active Member

    Apr 8, 2010
    I'm looking at some GPS modules linked below:

    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?

  2. retched

    AAC Fanatic!

    Dec 5, 2009
    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.
  3. wannaBinventor

    Thread Starter Active Member

    Apr 8, 2010

    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?
    Last edited: Nov 27, 2010
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    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.