Search results
Results from the WOW.Com Content Network
This is called CTCSS encoding. CTCSS tones range from 67 to 257 Hz. The tones are usually referred to as sub-audible tones. In an FM two-way radio system, CTCSS encoder levels are usually set for 15% of system deviation. For example, in a 5 kHz deviation system, the CTCSS tone level would normally be set to 750 Hz deviation.
CTCSS can be used to silence a radio until another radio with the same tone transmits. This allows monitoring of a channel for transmissions from radios set with the same tone without hearing other conversations that use different or even no tone. The use of CTCSS is not permitted on UHF CB repeaters or the designated emergency channels.
Most analog two-way radios utilize a technology called CTCSS or DCS that helps block out unwanted transmissions. To make MURS two-way radios work together, they must have matching CTCSS or DCS tones. This can usually be done via basic programming which almost all MURS two-way radios support.
CTCSS (Continuous Tone-Coded Squelch System) continuously superimposes any one of about 50 low-pitch audio tones on the transmitted signal, ranging from 67 to 254 Hz. The original tone set was 10, then 32 tones, and has been expanded even further over the years.
Systems generally use tones off of a single, designed tone plan. Individual tone plans are engineered to avoid overlapping or nearby tone frequencies that may cause falsing. Some systems use CTCSS subaudible tones as the tones composing the two-tone sequence. For example, a two tone sequence might consist of 123.0 Hz followed by 203.5 Hz.
FRS radios frequently have provisions for using sub-audible tone squelch (CTCSS and DCS) codes, filtering out unwanted chatter from other users on the same frequency. Although these codes are sometimes called "privacy codes" or "private line codes" (PL codes), they offer no protection from eavesdropping and are intended only to help reduce ...
As with FRS/GMRS and PMR446, the use of tone squelch systems such as CTCSS/DCS is encouraged. Like the PMR446, LPD433, Japan's 421–422 MHz SLPR service and KDR444 services, use of these frequencies in countries such as the United States is illegal without an amateur radio license as they fall within the 420–450 MHz 70 cm ham radio allocation.
Since 10 meters can frequently open up to propagate globally, most 10-meter repeaters use a CTCSS sub-audible access tone. 16 kHz-wide signals with 5 kHz deviation is normal in this band. 8 kHz-wide signals with 2.5 kHz deviation can also be found. 2.5kHz deviation is mandated by FCC rules below 29.0 MHz.