Here is a nice GPS antenna for APRS mode that is easy to build yet offers surprisingly good performance in a compact size. Best of all, it uses commonly available components and materials.
Connect the antenna to the GPS receiver and watch the signal-strength indicator.? You should see an improvement over the supplied stock antenna. You can tweak the antenna by bending the wires up and down gently and watching the results on your GPS unit. Be careful of the solder joint?it?s rather fragile. Adjust for maximum displayed signal. Repositioning the antenna may also improve reception. With this antenna, I routinely receive five to eight satellites on my Garmin II receiver.? If you are using a GPS unit that sends dc voltage volts up the coax to power an external preamp or amplified antenna, don?t worry. Since the elements are not grounded or shorted, there is no dc path.
Just be careful not to let either end of the active elements touch ground. [Be advised that some GPS receivers with internal patch antennas have an antenna switching circuit. This circuit disables the internal antenna when an amplified external antenna is attached. The receiver senses current flow that is intended to power the amplifier of the external antenna.? If your receiver has this feature, you will want the switch to activate and disable the internal patch antenna. Placing 1 k to 5 k across the ground and center conductor of the coax should be sufficient. Check with the manufacturer of your GPS receiver.
Visit Here for more.