Your Specialists in Radio and Navigation Equipment for use on Land, Sea and Air

UHF (Ultra High Frequency)

Q. Are there any special channels I should know about?
A. For 477Mhz UHF: channel 5 is your emergency channel, channels 1-8 are your repeater stations (refer below to Simplex and Duplex), channels 21 and 22 are data channels and may not be used for sending or receiving transmissions (new model radios block out these channels) and channel 40 is your highway channel used by most trucks. For 27Mhz CB: channel 9 is your emergency channel and channel 11 is your call channel.

Q. What is VOX?
A. VOX stands for Voice Activated Transmissions and allows the operator to have hands-free conversations. The microphone automatically detects your voice or other nearby sound causing the radio to transmit without the need press the PTT (push to talk) button.

Q. What role does Squelch play on a radio?
A. Squelch allows the operator to eliminate / close off background noise when there are no signals present. Strong incoming signals override this closed squelch to be heard in the speaker. Opening squelch allows background noise to be heard as well as allowing weaker signals to be received. Weaker signals may come through as a broken or chopped transmission by the squelch action.

Q. What are the group scan and open scan functions?
A. Open scanning allows the operator to pickup transmissions broadcasted on any of the 40 UHF channels. Group scanning allows the operator to pickup transmissions broadcasted on any of the programmed channels in the radio. Group scan channels may be user or dealer programmable depending on the type of unit and may include any frequency from the UHF band.

Q. What is selcall?
A. Selcall stands for Selective Calling System. This feature allows the operator to contact an individual or group of radios using coded transmissions known as ANI (auto number ID) to notify the corresponding radio of an incoming call.

Q. What is CTCSS?
A. CTCSS stands for Continuous Tone Coded Squelch System which provides quiet channel operation by blocking unwanted signals being received except those transmitting on your particular code. There are 38 codes per channel to choose from.

Q. What are Simplex and Duplex?
A. Simplex transmissions receive and transmit on the same channel as far as the operator’s setup will allow. Duplex transmissions utilise repeater stations around the country to onforward signals giving a greater transmission / receive range. Duplex channels are from 1 to 8 and transmit on one channel and receive on another. Eg: If the radio is set to channel 3, it will receive on channel 3 but transmits thirty channels higher on channel 33 through the repeater stations. All UHF radios have the ability to transmit using Simplex or Duplex.