Time trials testing multiple distentions of various concepts of equipment. In the case of the ARM micro processor (Raspberry PI) the test involves reliability and up-time. In the case of the antennas (a j-pole vs 1/4 wave) the reception range in all seasons. These antennas are placed in close proximity with both units feeding signal to the same SDR receiver setup. By permanently running this setup the effects of weather, humidity and even foliage on trees can be seen.
See the effect different antennas have on the ability to receive UHF ADS-B signals from passing aircraft.
Live view (as shown above): 1/4 wave dipole ADS-B Aircraft tracking ground radar can be seen at http://adsb.steeman.org
Live view (as shown above): j-pole ADS-B Aircraft tracking ground radar can be seen at http://adsb2.steeman.org
In other articles I'll go into the details of building these and other UHF antennas.
The quarter wave antenna is as the name states, a quarter of the wavelength long. For 1090 MHz with a wavelength of 269.228 mm it makes the active antenna element 68.807 mm or 6.8 cm long.
This type of antenna requires a ground-plane (virtual mirror reflection of itself) to operate, hence the four (or more) ground-plane elements at the base of the active element. These are bend down at an angle of 45 degrees for impedance matching to 50 Ohms.
Quarter wave antennas require a large volume of space to operate and are not ideal for use in cramped areas, nor do they produce any gain (signal amplification).
The J-Pole antenna, depending on how you look at it, is a full wave element, using a half wave stub for impedance matching purposes. The quarter wave (short) section is grounded while the three quarter wave session is the active element.
It is longer than the 1/4 wave, but requires less volume the short element is 68.807 mm the long element is 206.422 mm. The distance between the elements (+ or - for matching) is 6.730 mm. This antenna goes not require a ground plane, but does require a balun. The balun for this type of antenna matching is to prevent current flow on the transmission line.
J-Pole design antennas are ideal "pipe antennas", which can easily be inserted into a section of PVC pipe to protect them from the weather.