by Frank Moss
The mobile radio is a tried and true method for communications in the field. Modern technology has increased range and clarity while also allowing for add-ons like voice scrambling. The FCC regulates and licenses some of the more “prime” radio frequencies, but with the demise of UHF Analog Television Broadcast, there are now other frequencies that are available.
Frequency and Wavelength
A good chart on broadcast distance for the below selections is located here. Though MF and HF have good transmission distance, they are not practical for portable radio solutions due to antenna length requirements.
- Frequency is how often a signal cycles in a given amount of time (seconds).
- Wavelength is the distance between peaks of a signal’s cycle.
- Medium Frequency
- 300-3000 kHz | 1 km – 100 m
- AM radio broadcast (US)
- High Frequency
- 3-30 MHz | 100m – 10 m
- Shortwave Radio, CB, RFID, Over-The-Horizon Radar, Maritime Telephony
- Very High Frequency
- 30-300 MHz | 10 m – 1 m
- Amateur/HAM radio, Aircraft, Maritime and TV Broadcast, MURS
- Ultra High Frequency
- 300-3000 MHz | 1m – 100 mm
- Television, Radio Astronomy, Mobile Phones, WiFi, GPS, GRMS/FRS
Family Radio Service is a short range, unlicensed range of frequencies. The maximum power rating for transmission is 500 milliwatts, which ensures short range; less than 1.5 miles. The FCC does not require a license for use of the FRS Spectrum due to short range and low wattage limitations even though it shares frequency with GMRS. For a list of investigated radios see GMRS
General Mobile Radio Service does require a $75.00 license, but no test. Users are allowed up to 5 Watts of transmit on FRS shared frequencies and 50 Watts transmit power on GRMS only channels. You should not use frequencies listed for use by “Repeaters” and many radios will not allow it. Most commercial off the shelf (COTS) handheld units will operate at 5 watts for adequate battery life. This can be range limiting outside of line of sight, but used in conjunction with a mobile radio that can send and receive at 50 watts of power can work well in SOME limited line of sight situations. However the more powerful mobile transmitter will overpower the weaker handhelds. Units looked at in our research have been:
HAM radio transmissions require a license that can only be acquired after passing a test. The FCC will also issue you a Radio ID (or you can request a Vantiy ID). There are three levels of radio licenseTechnician, General, and Amateur Extra more information can be found here.
Multi-Use Radio Service used to be called the Color Dot class. There are no individual licensing requirements and can be used for personal or business reasons. The frequency range is in the 11.25/20kHz range and limited to 2 watts of transmit power. MURS radios give about twice the distance of GMRS radios. You can find more information on MURS here. These radios are more expensive than GMRS/FRS options.
CB radios have been around since 1945 and use 40 channels within the 27 MHz range. These radios require a lengthy antenna and do not have very good in building signal penetration. Handheld devices suffer transmission distance and clarity due to short antenna’s inherent to portable design. Look for Cobra radios which are very popular choices for the crowded CB radio bands.
More info here.