Introduction

The GPS comes generally with a small one inch patch antenna.

While this antenna has a good sensitivity and a small size, you probably noticed some positioning errors due to indirect reception path, especially in urban areas or close to a wall.

The backfire helix antenna is quite easy to build, cost near nothing and definitively solve this position error problem.

Various helix antennas can be found, i used this one as a guide : http://lea.hamradio.si/~s53mv/navsats/analog.html

Most GPS provides power through the antenna connector, in this case i had to add a 18pF capacitor for DC blocking purposes and avoid a short circuit with the new antenna.

A classic ceramic capacitor can be mounted on top antenna. Value is not critical, just select one from 10pF to 47pF.

I also did the same modification with a M8N module that has a built in magnetometer.

Another example using a SMA connector, the DC blocking capacitor is soldered between the antenna pin and SMA connector, close to the GPS module on other pcb side.