A common and practical antenna is the quarter-wave (¼ λ) vertical, sometimes called a monopole. It simply uses one leg of the dipole in an upright, vertical position and the other leg of the dipole is replaced with a flat plane or perpendicular radials. Moteinos with transceivers include a monopole wire antenna that you can solder to the “ANT” pinhole for an out-of-box cheap and quite effective antenna.
Examples of quarter-wave verticals, for 1GHz and 2.4GHz respectively:
|¼ λ vertical with 4 radials||¼ λ vertical with a ground plane|
(notice the feedline with SMA connector)
Since the most recognizable part of the original dipole in these antennas is the vertical element sticking up, this antenna is often referred to as a monopole antenna. The term monopole is misleading as this type of antenna needs two elements for proper operation. Even though the ground plane or radials may not look like a ‘pole’, they are essential for making the antenna work.
Another variation of the quarter-wave vertical is the Helical antenna, shown below:
|‘Rubber Ducky’ antenna|
on a handheld transceiver
|Helical on a small radio|
The straight vertical element has been coiled up, mainly to make it conveniently short as this is for a handheld radio. The body of the radio acts as the other half of what essentially still is a dipole antenna. By its very nature, the coiling of the radiating element like this creates an inductor and requires a complete re-evaluation of the antenna to ensure optimal performance.
With the PCB (printed circuit board) acting as the ground plane for a quarter-wave vertical antenna, it now becomes clear how the Moteino circuit board acts as the ground plane for the supplied antenna wire:
|¼ wave vertical wire antenna on a Moteino|
|And here on a MotionMote kit|
To further improve the antenna system you could either extend the ground plane or add ground radials (connect to the nearest GND tracks). However, even in this configuration the Moteino antenna system works surprisingly well.
Another way to add an antenna to the Moteino is to make use of a small PCB edge-mounted SMA connector. This allows you to easily interchange antennas without having to de-solder anything. Here is a moteino with PCB edge SMA connector and a small helical antenna:
Moteino also accepts u.FL connectors which are useful to route the signal from inside the enclosure to an external mounted antenna.