M4 GPS Antenna Options
Enlarge the Groundplane of the GPS Antenna
DIY Dipole GPS Antenna
List of possible Antennas suitable for M4 & other AQ boards
Ceramic patch antennas
PCB/Ceramic antennas, Omnidirectional

M4 GPS Antenna Options

The M4v1 comes with an on-board UBlox 7 GPS module (M4v2 uses an M8Q module). All you need is an external antenna. There´s a variety of antennas being tested. Listed below*

A great tool to determin health and accuracy of your Ublox GPS modules and antennas is the Ublox
u-center GNSS evaluation software for Windows. You can download it here. Use a USB/UART connection at a baud rate of 1200 in the tool´s “Receiver” menu.

Download and install uBLOX uCENTER GNNS software.
Connect to the USB COM port at 1200 baud (tells the M4 that you want to speak directly to the GPS.) Turn on the NAV_SAT messages and you will get a graphic representation of satellites received, strengths and positions. GPS type is ublox8 for the M4r6 V2 production boards and uBlox7 for the BETA boards.

Note: a very first fix of a GPS module fresh from the factory can take 15 minutes and longer, depending on reception conditions. So just place your M4 with a fresh lipo in an open space and let it gather satellite data. On the M4v2 the GPS data will be buffered by a backup battery. Depending on the used antenna (active/passive, size etc.) you will be able to get a 3D fix and accurate coordinates in a very short time.

Enlarge the Groundplane of the GPS Antenna

Examples for Groundplanes. Image by Astudillo. Reference: http://forum.autoquad.org/viewtopic.php?f=40&t=4253

Thickness does not matter. Basically any material with a conductive surface or inner conductive plane would work.

As for size: basically the more, the better. For a 10mm antenna use at least 30 mm diameter.

Distance from the FC itself is a factor too. So the higher you can lift the antenna up off the FC surface, the better.

DIY Dipole GPS Antenna

Cheapest option is a simple DIY dipole antenna, derived from an antenna cable.

Dipole antennas or small ceramic patch antennas will never be able to achieve the same performance as a 35mm active antenna. Please keep that in mind when trying autonomous functions with mini sized Quads.To get the best reception you should mount the antenna as far away from the FC as possible. A bigger ground plane will also help with the small active ceramic patch antennas.

You can order a cable with connectors from Viacopter

Shorten the cable to your needs and dismantle the outer isolator. Cut the wires to 4,6cm length and put some short pieces of heat shrink over both ends.

To strenghten the dipole you can use some plastic rods or similar to keep the T shape.

We´ve been testing these with good results: a 3D GPS fix can be achieved in around 30-40secs.
However you can´t expect solid GPS reception at any conditions.

The longer you wait the more precise the navigation will be since it takes a while until you get an HAcc (horizontal accuracy) of less than 1m. A 2D fix will start at an HAcc <4m, a 3D fix will start at <3m. An HAcc of less than 2m is good enough to fly missions and get a good position hold.