Technical Manual

EX7100 Technical Manual - Module Descriptions

7.9 VHF Duplex Filter Module Type 8013

7.9.1 General

The Duplex Filter (or Duplexer) allows the receiver and transmitter modules to be

connected to one antenna at each terminal.

This is achieved with selective filtering. At the receive frequency the antenna port of the

Duplexer is connected as directly as possible to the receiver input. Similarly at the

transmit frequency the antenna port is connected as directly as possible to the transmitter

PA output.

The Duplexer isolates the receiver from the large signals produced by the transmitter. In

addition, it provides significant protection against lightning damage to the radio.

Note: The use of suitable earthing and an external lightning arrester is recommended at

all times, refer to Section 2.6.1 for further details.

Three VHF Duplexer variants are available, covering 138 to 156MHz, 148-162 MHz and

152 to 175MHz.

Note: The duplexer Tx and Rx notches have a bandwidth of only 100kHz. This means

that when changing the EX7100 frequencies by more than two channels from

centre frequency, the duplexer will need to be re-channelled

VHF Connections

The Duplexer module has three connection ports: Antenna, High and Low.

Antenna Provides RF connection to/from the installed antenna.

High Connection is dependent on the Tx and Rx operating frequency pair. If the

Tx operates on the higher frequency, the High port connects to the PA

output (PL102). If the Rx operates on the higher frequency, the High port

connects to the Receiver Front-End input (SK101).

Low Connection will be the reverse of that detailed above, dependent on which

module is using the lower frequency.

VHF Mounting

The Duplexer module is mounted on the underside of the Top Cover via 4 threaded studs

and associated fasteners When removing the Terminal top cover, care should be

taken to avoid damaging the duplexer’s flying leads.