When making decisions on buying radios, remember this "Rule of thumb": the lower the frequency the longer the wave length or the better/further it will travel across land, go over hills, etc. The higher the frequency the shorter the wavelength but the better penetration power it has through a building and in a straight line.
Examples:
25-35 mhz (lowband) approximately 2 miles/watt (has sun spot problems - antenna is approximately 36" for a ¼ (wave) antenna.
140-175 mhz (highband, VHF) approximately 1 mile/watt antenna is approximately 18" for ¼ wave (includes marine band for talking across water). Good, all-around radio for talking across land, hunting, fishing, traveling, etc.
450-470 mhz (UHF, GMRS) approximately ½ mile/watt and is approximately 6" long for ¼ wave. Good for business, talking through buildings and using repeaters. Not so good for open area because the wavelength is too short and straight.
Note: FRS radios fall under this class at ½ watt (500 mw). No license required which is not good for talking across water, not good for open land, good for approximately ¼ mile not the 2 miles usually stated.
800 mhz ( most police departments) is good for approximately ¼ mile/watt (handhelds are turned down to 2 watts per OSHA/FCC for radiation exposure). Very good for buildings but bad for outdoor use. These frequencies are usually trunked (LTR). Because of their short wavelength, more repeaters are needed to cover a city, etc.
This is also where the analog cell phones are. Because of the longer wavelength (800mhz) analog vs. digital (2000 mhz), you have less dropped calls depending on your carrier.
2000 mhz (2ghz) where you will find digital phones, PCS, etc. The wavelength is approximately 1" and the power is turned down to .1 watt because of possible damage to cell tissue in your brain (big controversy). Many, many towers are needed to cover an area to prevent dropped calls.
There are 3 types of modulation:
AM (Amplitude Modulation) - CB radios are affected by all forms of sunspots, power wires, under bridges, and skip.
FM (Frequency Modulation) - Not affected by any of the above problems under AM. All business radios, goes in a straight line, can usually operate on repeaters. The power and height of the transmitter dictates the length of the transmission, or range of communications.
PM (Phase Modulation) - Used in radar etc. Not generally used for any form of verbal communications.
Increasing range/communications coverage:
To increase your ERP (Effective Radiated Power). For every 3 db (x2) gain in antenna height (5 -10 ft, 10-20 ft, 20-40 ft.) you will effectively double (3 db gain) your power out. (5 watts would be equivalent to 10 watts, etc.) This also works in radio reception. In other words, if you want to talk and hear better, climb up on a rock, hill, mountain, or building.
