GPS antennas

GPS receiver

Most Medusa spectrometers with an onboard GPS receiver use a uBlox ZED-F9P or uBlox ZED-X20P GNSS receiver. This chip can capture GPS, QZSS, GLONASS, Galileo and BeiDou signals. Modern Medusa systems use the L1, L2 and L5 frequency bands. At minimum, the L1 band is needed to acquire a valid GPS position.

Medusa spectrometers with an onboard GPS receiver are outfitted with one of two different GPS connectors, depending on the model. The MS-100, MS-350, MS-700 and MS-1000 use an SMA connector. The MS-2000, MS-4000 and MS-20k use a TNC connector, which is slightly larger.

Antennas

A GPS antenna is required for satellite reception. GPS antennas mainly differ in how clean a signal they deliver to the receiver, not in what they receive. More expensive antennas include better filtering, which reduces noise before the signal reaches the GPS chip.

In practice, a better antenna typically means more satellites tracked, especially under trees or near buildings where weaker signals would otherwise drop out. More satellites does not automatically translate into a better position, though. Once the receiver has enough satellites with good geometry to fix an (RTK) solution, additional satellites mainly add redundancy rather than accuracy. Position quality depends more on signal cleanliness and satellite geometry than on raw satellite count, which is why it is possible to reach centimeter precision even with lower cost antennas.

Both SMA and TNC connectors are commonly used, and many different GPS antennas are available. Most antennas will work with the Medusa spectrometers, as long as the connector matches or a suitable adapter is used.

Our detectors accept both active and passive antennas. When using an active antenna, the port supplies 3.3V bias voltage, current limited to 50 mA. LNA gain range follows uBlox specifications.

Recommended antennas

The antennas listed below have been tested successfully with Medusa spectrometers. In practice, most antennas meeting the specifications above will work.

SMA connector systems

The following antennas have been tested and are known to work.

Antenna	Notes
Siretta MIKE3A/0.5M/SMAM/RA/S/17	Available in various cable lengths. Recommended
u-blox ANN-MB2	Better quality, larger housing and longer cable
Maxtena M1516HCT-15A-SMA	Stubby antenna without cable. Recommended
JC Antenna JCA228F	Best GPS quality, largest housing

TNC connector systems

The spectrometers with a TNC connector are supplied by default with a JC Antenna JCA228F.

Ordering

The GPS antennas can be ordered through Medusa Radiometrics, but ordering directly through a dedicated supplier is usually faster and cheaper.