Codan Radio Radio Repeater Systems Training Guide - Manual (Page 23)

RADIO REPEATER SYSTEM | TRAINING GUIDE
Chapter 2: Repeater System Confi gurations Page 15
CTCSS
Where frequencies are congested, the authorities may require frequency sharing, in which case it will
be necessary to use some type of CTCSS (Continuous Tone Coded Squelch System) as shown in
Figure 2-8. In such a system all mobiles, portables and base stations are provided with a sub-audible
tone-encoder on the repeater channels. Each repeater uses a tone-decoder. These units are operating
continuously when your microphone transmit button is depressed. Another signal on the same VHF or
UHF frequency cannot activate the receiver at the repeater because it would be allocated a different
CTCSS tone. This gives the appearance of a quiet channel all of the time although there can still be
interference between users if both come on channel through their own systems at the same time.
Figure 2-8: CTCSS Protected Repeater Systems
OTHER CONFIGURATIONS
Another confi guration option for radio systems is telephone interconnects. Interconnects are usually
electrically located between the base station and the telephone company lines. They enable mobiles
to receive and initiate normal telephone calls.
Most authorities require that they be compatible with the telephone system, cause no electrical
interference, and be controlled by the mobile, not the telephone caller. From a repeater users’ point of
view, the most important requirement is that an interconnect has timing devices that enable its use and
control through one or more repeaters.
The ultimate test of which interconnect to purchase is whether it will work on your repeater system. By
entering the proper sequence of DTMF tones, the mobile user is able to dial either pre-programmed
telephone numbers or any other telephone number. Limitations on length of call, restrictions on use of
long distance numbers and other features may be programmed into the interconnect unit.
Mobiles A Mobiles B
Repeater A Repeater B
Tx-F1
Rx-F2
CTCSS
Tone A
Tx-F1
Rx-F2
CTCSS
Tone B
Possible Interference
Tx-F2
Rx-F1
Tx-F2
Rx-F1