Transmissions from your marine radio to destination sources will lose partial brevity along the way, meaning only parts of your signal gain are actually plausible. When shopping for antennas, another major component taken into account is the SWR, or Standing Wave Ratio. In electronic transmission lines, a specific voltage value is assigned which dictates its ability (or the lack thereof) to keep signal when sent miles away. Mathematically speaking, this ratio measures nonconforming electromagnetic fields on coaxial cables or similar lines being used in marine radio antennas. In SWR nomenclature, there are three known types:
- ISWR, or the antenna’s electrical current ratio;
- VSWR, which values the voltage;
- PSWR, the square root of VSWR figures which measures power.
Although arbitrary to some, the Standing Wave Ratio plays heavily into astute marine antenna buyers.
What Standing Wave Ratio Is Best?
Ideally, having perfect 1:1 antennas (which lose no signal) would appease every boater, and prove to be money well spent. Logically, then, your goal is getting as close to ‘perfect’ antenna transmission ratio as possible. You’ll find many antenna manufacturers dance around the 1:1 mark; today’s standard strengths range from 1.2:1 to around 1.4:1. Factually speaking, the higher your ratios go upward, the more wasted signals you could expect – a vital component when your intended target is miles away. Transmitter antenna’s impedance must be properly tuned to match coaxial feed line using specific meters, or your antenna will improperly work – or throw weaker signals than their decibel ratings.
Antenna Shape Matters
Your antenna’s tip shape matters considerably when signal broadcasts are being made. Since round antennas will throw signals with more circumference than squares, you’ll need to avoid any shapes which take away impedance since your SWR will plummet into the 5:1, 8:1 range regardless what rating it states. Having particularly low angles of radiation also matters considerably, too, since radiation intercepts outgoing transmission waves and negates them. Round, even elongated, antennas will throw signals further into the air and should be equally considered to have a lower Standing Wave Ratio.
Why Measuring SWR Is Vital
Leisurely boating perhaps doesn’t appear threatening, yet consider this: when you’ve found yourself 5 miles from shore, stranded and have only your radio, it’s probably an excellent idea it works. With lower ratios, you’ll lose less signal when radioing for help. Nearly every antenna will experience weakness in signals, albeit fractionally; your goal is having strong coax cable and SWR’s closely matching that cable’s impedance. As previously stated, you’ll probably never find 1:1 standing wave ratios in our lifetime, yet coming within decimal points of perfection should be your primary goal when boating miles away from civilization.
Asking Before Buying
Your antenna manufacturers really don’t display their guideline or definition of standing wave ratio for consumers to view. Shakespeare Electronics, makers of fine antennas and general marine gear, could help consumers achieve the tightest ratios since they’re always studying methods of equalizing coax and antenna impedance. If antenna savviness becomes part of your marine antenna buying repertoire, calling the manufacturer directly will give perhaps the best indication which height, construction, masthead fastening and decibel levels will offer best antenna efficiency, which ultimately is what standing wave ratio measures.