First the summary:
– If you want a very low cost and easy to make DIY antenna, make a Spider or Cantenna. Both can be used indoors as well as outdoors. Their gain is not high (about 2 dBi), and their performance is substantially enhanced if you use an amplifier. If your coax length is longer than 5 meters / 15ft, an amplifier becomes essential.
– If you want a good quality high gain (5 to 6 dBi), mechanically strong outdoor antenna, purchase Flight Aware 1090 Mhz antenna from Amazon.com. It is good, and very reasonably priced.
Now the detailed explanation…
(1) Any antenna placed outdoors (in yard, on roof or on mast), performs better than same antenna placed indoors (in attic or near a window)
(2) The maximum range is achieved if antenna’s location & height is such that it can “see” the horizon all around or in most directions. Raising antenna above roof lines of surrounding buildings, houses & trees improves range greately.
(3) Under DIY hobbyist conditions, it is very easy to make a collinear antenna (coaxial or wire or strip line), but very hard to get it right. Only a few lucky DIY hobbyists succeed in making a good collinear, and most end up with a poor collinear antenna. The reasons are:
(a) In order to succeed in make a good collinear, proper test equipment & technical know how are required. Most hobbyists dont have these.
(b) The collinears have very low dimensional tolerance. Few mm error in dimensions due to either poor design, or inaccurate construction, throws the collinear from “excellent” to “poor” category. A lot of collinear designs posted on internet are inaccurate or flawed.
(4) Under DIY hobbyist conditions, the 1/4 wavelength groundplane antennas (Spider & Cantenna) are easy to make, and easy to get right. These antennas are:
(a) Naturally tuned, so dont require any test equipment and technical know how.
(b) Have large dimensional tolerance, and perform fairly good even with few mm error in dimensions.