Portable VHF two-way radios operate at low power thereby reducing optimum range of communication. This limited range is extended with the installation of a VHF repeater system. But, commercially available repeaters are expensive.

The Carrier-Operated Relay (COR) for VHF repeater is developed to primarily generate a large amount of savings. It is interface to a build-it-yourself repeater. It also eliminates splatting or desensitization that reduces sensitivity of the receiver; and monitors overheating of the repeater transmitter that could damage the transmitter itself. Since the COR operates on the mechanical switching of the relay, contact closure creates wear and tear that deteriorates relay over years of operation. The project is composed of different circuit modules which are assembled inside a single steel casing. Surface mount soldering technique is employed to eliminate the need of drilling for electronic component's terminal.

The acceptability of the project is evaluated using qualitative survey method. Thirty respondents were asked to rate the project after they were shown the project demonstration and testing. The survey yielded a very satisfactory rating.

Based from the results of the survey and the outcome of the tests conducted on the project, it is concluded that the Carrier-Operated Relay (COR) for VHF repeater is acceptable and operational. However, a single antenna for both transmission and reception is ideal for the repeater system. Also, installation of brush-less fan is considered for an improved heat dissipation. The utilization of Short Messaging Services (SMS) to access the repeater remotely is commendable instead of a dial-up call. Regular charging of cellular phones battery is likely observed to facilitate access of the repeater system anytime and anywhere.

In this communication age, telecommunication technologies span from basic connectivity to complex adaptability. Its ever-evolving technology became ever more dynamic with the advent of mobile phones. Thereat, communication boundaries are crushed. Access to the bigger world has been opened. Communication opportunities previously unavailable in a certain area are now bridged through cell sites installations. The state-of-the-art telecommunication gadgets underwent a shift in social status to answer the growing individual demands. Consequently, cellular phones are indispensable items of today's existence due to the significant role of communication.

However, in case of great distress or misfortune, such as fire, flood, earthquake typhoon and other disastrous accidents which require rescue operations, constant communication is aptly observed. Cellular phones for reasons of unfit application and unsuitable condition fail to wholly accommodate the communication need in this aspect. Apparently, it would be impractical and unwise to stay connected at frequent times due to it  charged rate when utilized.

Unforeseen event or condition requires prompt action. The standard operating procedures to be complied by the rescuer present on the scene is to call for assistance from other members of the rescue groups. This is favorably done with the aid of the two-way radios or transceiver that performs an important function in establishing communication between mobile stations at any hasty impulse.

On the other hand, portable transceiver units operate at low power thus; the optimum range of communication is reduced. This means a limited area of coverage that causes restrictions on the part of the user to communicate outside his radios coverage. This uncompromising condition which also applicable to military operation at war is solved with the institution of the repeater system. A good repeater extends the transceiver operation in terms of range and functionality. Thereby, providing ease for rescuers and militaries to attend their duties quickly and efficiently in giving assistance to different affected areas at times of calamities and state emergencies. But, a complete installation of a commercially available repeater system is a big factor in terms of cost to be reckoned by volunteers of rescue groups who do not have enough funds to avail it.

All these problems discussed on every detailed angle have been floating on the air until the time it was thought of . That is when a commencement of this study was raised and developed.

A good Carrier-Operated-Relay unit (COR) interfaced in the VHF repeater system shall facilitate reliable service:

Specifically the study aims:

1. To develop a low cost COR for a "build-it-yourself" repeater.

2. To eliminate splatting or desensitization that consequently reduces the receiver's sensitivity.

3. To monitor overheating of the repeater transmitter that would cause transmitter failure.

The Carrier-Operated-Relay (COR) operates under a frequency preferred by the user provided the said frequency is within the VHF band. The COR circuit operates on its built-in 12 volts regulated power supply that has the capacity to deliver 15 amperes of current to ensure the proper operation of the entire circuit including the high power repeater transmitter. Its thermostat sensor monitors the amount of heat generated by the repeater transmitter during retransmission. Thus, preventing it from overheating due to cases where the repeater system is being keyed by unauthorized individuals. It also offers optional remote accessing to the repeater system with the aid of a cellular mobile phone. However, this feature will not function if the cellphone battery is empty. Since the COR operates on the mechanical switching of the contact relay, one worst-case scenario is when mechanical failure occurs that would cause transmitter failure.