Antennas Basics for Survival – A Glossary for the Radio Communications Uninitiated – Message One
So far, we’ve discussed a lot of aspects of various communications services. One thing that stands out among the TOP most important aspects of anything having to do with communications is your antenna.
Without an antenna a radio transmitter, or a receiver are virtually useless. In fact, a radio without an antenna might as well be used as a paperweight or door stop. With that said, let’s look at some real physics for a bit. Don’t get wrapped around the axle with the math or physics, but I’d really like for everyone to have a working knowledge of antennas before they go on and do much else. The reason is an antenna can be manufactured from simple wire, and perhaps about anything else that is conductive, including rusty bed-springs, slinkys (remember those?), copper pipe, metal tubing, and perhaps about anything else that can be cut and/or tuned to a given frequency.
The next few articles will deal with radio antennas specifically. This particular post will be a glossary that will be updated as necessary to contain as much information as possible for you to refer back to when necessary. I will add them as we go. I will make this a message all by itself – with a kind of glossary you can refer to when you run into a phrase or a word you don’t know or don’t understand. If for some reason you still “don’t get it”, post a message about the subject, especially if it is a glossary definition and I will correct or update the message with more information.
Let’s look at some terms and definitions first. Again, don’t worry too much about terminology until it becomes critical for you to understand a word I’ve used.
Antenna: Any tuned device that can be made to radiate radio frequency energy. The same device can be used to receive signals as well.
Capacitor: An electronic device capable of storing an electric charge. Is used in everything from power supplies for filtering out noise and cleaning up signals to RF systems for tuning. -|(- (ÃŸ a schematic symbol)
Coil: A coil of wire, usually cut to a certain length and wound around a specific sized core, usually air-core which can be used to tune circuits.
Dipole antenna: Usually a straight, center-fed, one-half wavelength antenna.
Extremely High Frequency (EHF, millimeter wave signals): The band of frequencies from 30 gigahertz to 300 gigahertz. Called millimeter wave signals because the wavelength is in the millimeter measurements, instead of meters.
Extremely Low Frequency (ELF): The band of frequencies from 0 to 3 kilohertz. (That is 0 cycles per second to 3000 cycles per second.)
Frequency: An alternating current that appears as a SINE WAVE when plotted out, having a set of valleys and peaks, alternating at a given rate, usually in cycles-per-second. For instance, 60 Hertz (also called 60 cycles per second) has a sine wave that occurs 60 times in one second. A radio frequency is simply a very high frequency, for instance, 150 Mhz, or 150 million Hertz, or 150 million cycles per second.
High Frequency (HF): The band of frequencies in the radio frequency spectrum ranging from approximately 3 Megahertz to 30 megahertz. This area of the spectrum contains a majority of the Amateur Radio (ham) bands, all the shortwave bands, the upper end of the AM band, weather stations, aircraft, ground control stations, and many signals can be heard there. Signals like voice in various modes, digital signals, facsimile, Radio Teletype, Morse code and others will be heard throughout these frequencies.
Low Frequency (LF): The band of frequencies from 30 kilohertz to 300 kilohertz.
Medium Frequency (MF): Also known as the Medium Wave Band, this is from 300 kilohertz through 3000 kilohertz.
Schematic: A drawing or diagram containing electronic symbols and wiring information for circuits.
Super High Frequency (SHF): The band of frequencies from 3 gigahertz to 30 gigahertz.
Tuned-circuit: A circuit containing a coil and capacitor, also known as inductance and capacitance.
Ultra High Frequency (UHF): The band of frequencies between 300 megahertz to 3000 megahertz.
Very High Frequency (VHF): The band of frequencies between 30 megahertz to 300 megahertz.
Wavelength: This is the physical length of a single (usually radio frequency) sine wave cycle, measured at the zero reference point, to include exactly one cycle. The simple calculation for the wavelength is: l= C/f . Where: C= speed of light in either meters-per-second, or miles per second. Your answer will be in either meters or feet. f = frequency in hertz (or cycles per second) and l= (Lambda =) the wavelength of the single cycle. This particular calculation will generally give you the length of wire for a full wavelength antenna and is necessary to know about how much space you will need for an HF antenna or the lower frequencies. The higher you go in frequency, the shorter the wavelength will be.
A couple of nice charts on the spectrum can be found here: http://www.ntia.doc.gov/osmhome/allochrt.pdf