Which one is the best antenna?
If there was just one “best” antenna, everybody would use it. The best antenna for one particular situation may not work well somewhere else. There are three rules of antenna installation:
• Any antenna is better than no antenna.
• Bigger and higher are generally better. If small antennas really did work as well as big antennas, nobody would spend the time, money and effort to put up the big ones.
• Every antenna installation is a compromise.
There are several factors that must be considered when engineering an antenna installation. Height? Size? Weight? Restrictions? Cost?
Now there is a factor that we all have to compromise on with every antenna, cost. Should I build it or buy it? Many antennas can be scratch built for a fraction of what they cost readymade, but are they bargains? Mostly antennas are advertised for $75 to $150 but the same performance can be had from a home built antenna costing less than twenty dollars. A vertical antenna can be constructed from a 1 to 2 meter piece of coax (coaxial collinear) or electrical copper wire, or aluminium, brass, or copper tube (1/4 wavelength groundplane, wire collinear with coils & franklin collinear with hairpin stubs) for a few bucks. However they may be difficult to design and tune (except the naturally tuned 1/4 wavelength groundplane) if the Amateur doesn’t have a background in engineering or key pieces of test equipment. The truth is, when you buy a ready-made antenna, you aren’t just buying a collection of coax, wires, tubing, and connectors, you are also purchasing design expertise.
Do you get your money’s worth? Is the kit of parts complete? Is the hardware stainless steel, or are you going to have to deal with a corroded mess after a couple of years? Are the directions clear, and detailed? Some antenna manufacturers provide a single sheet with a quick sketch whereas others provide a manual running to several pages. Usually the bulk of even a complex antenna is fairly straightforward in assembly, with a single part requiring tuning. When you get to the tuning, either (1) the manufacturer has designed the assembly so it could be tuned at the factory; or (2) he has provided detailed instructions on how to accomplish the procedure; or (3) the instructions are vague and misleading; or (4) you are left on your own. The author has experienced all of these conditions.
The quality of the instruction manual is of primary importance when selecting a ready-made antenna. Some engineer built a number of prototypes to come up with the design the manufacturer decided to market. Assuming they started with exact copies of the pieces of that antenna, the manual should lead you by the hand to assemble those pieces into a good enough copy of the original to equal the performance advertised. A low cost antenna is no bargain if you cannot properly set it up for peak performance.
What should be height of ADS-B receiving antenna? The range is basically determined by height of the aeroplanes which are several thousand feet high. However the receiving antenna should be high enough for low flying aeroplanes, and to overcome obstructions of terrain (such as tall trees, buildings, hillocks etc). In many cases, a tower isn’t necessary. When you think “tower”, remember that your house roof may already be a good height already.
One way to answer the antenna question would be to ask, “What does a ‘typical’ ADS-B amateur use?” There is no ‘typical’ ADS-B station; any more than there is a ‘typical’ amateur. However, given the same engineering problem, the solutions tend toward a common theme. Some ADS-B amateurs, who routinely receive ADS-B, have a tower. The most common height is in the 60-70-foot range. On the top of the tower is mounted a 0.5 to 1.5 meter antenna. There is then a coaxial cable running into the receiver. Is this the “best” antenna? Not necessarily. Many amateurs have to compromise this arrangement due to zoning laws, and deed covenants. This arrangement may not be possible in all locations.The best antenna for you will be as personal as the best pair of shoes would be. Simple, easy antennas are a smart start. You can start with a dipole (1/2 wave or full wave or 4 or 6 element franklincollinear). More elaborate (and expensive) antennas should be carefully researched. The experienced Amateur should be able to decide what limitations his or her own situation imposes on the potential choices.
Objects and landforms in the environment profoundly affect radio waves arriving at an antenna. Will the antenna be ground mounted or elevated? Close to a building or in the clear? Mounted on a tower, pole, building? How much will the whole installation cost? Will the neighbors (or spouse) object?
The antenna system is the single most important component of an ADS-B receiving station. It defines the performance of the entire station. Consider the choices carefully, because only you can really answer the question:
What is the best antenna?
***Adapted and modified for ADS-B by abcd567, from an article written by Amateur Radio Operator NM7R for ham radio amateurs.