Procom have recently added two new filters to its wide range of RF filtering products. The LP 174-FME is a Low-Pass filter with a pass band of 0-174MHz and a stop band of 380-1000MHz. The HP 380-FME is a High-Pass filter with a pass band of 380-1000MHz and a stop band of 0-174 MHz.
The LP 174-FME and HP 380-FME are designed together to avoid possible interference between VHF radios and TETRA radios. A couple of examples being with two vehicles being near to each other and using different radio systems, or in vehicles where both VHF and TETRA radio systems are being used and operated either with a common multiband antenna or on two separate closely spaced antennas.
In this, or similar situations, three types of disturbance can occur:
• Possible harmonics from the VHF transmitter can disturb the reception of TETRA signals.
• The TETRA transmitter signal can overload the VHF receiver input, thus disturbing or blocking the VHF reception.
• The VHF transmitter signal can overload the TETRA receiver input, thus disturbing or blocking the TETRA reception.
By inserting the LP 174-FME into the VHF radio antenna cable, the TETRA radio will be protected from harmonic signals from the VHF transmitter. The VHF receiver will also be protected from overload from the TETRA transmitter signal.
By inserting the HP 380-FME into the TETRA radio antenna cable, the TETRA receiver will be protected from overload from the VHF transmitter signal.The filters can also be used separately as harmonic filter or pre-selector in appropriate VHF or UHF radio systems.