Product Manual

Product Manual for Tornado Radio Unit
29
7 DUPLEXER TUNING GUIDE
The Mimomax Tornado radio unit has two transmitters and two receivers; these connect to two antenna ports via
two duplexers.
The duplexer serves three primary functions.
• It allows one transmitter and one receiver to be connected to a single antenna port.
• It reduces the high-power transmitter signal getting into the sensitive receiver, and the received signal
getting into the transmitter.
• In the case of the 400MHz Tornado duplexer, the Low Noise Amplifier for the Receive path has been
integrated onto the duplexer printed circuit board.
This manual covers internal duplexer tuning for 400 – 470 MHz radios. 700 MHz radios do not require duplexer
tuning and duplexers should not be tuned in the 900 MHz range. VHF radios do not have internal duplexers.
7.1 DUPLEXER TUNING
The 400-470 MHz internal duplexers are designed for a TX to Rx frequency difference of 5MHz or greater. The
filters are band pass filters with tuneable notches at +/-the difference in frequency. Given that notches appear either
side of the pass band, the duplexer can support TX high or TX low configurations. Note: TX high means the
transmitter frequency is above the receive frequency. TX low means the transmitter frequency is below the receive
frequency.
The 3dB pass band is nominally designed to be 3.5MHz. However this will vary slightly across the band. It will be
slightly wider at the top of the band and narrower at the bottom of the band. The insertion loss is typically 3.4dB in
the pass band. Insertion loss will vary across the band, being less at the top of the band and more at the bottom of
the band. The Tx notch depth is designed to be >60dB at +/-5MHz. Note that this improves as the other path is
tuned up and typically with both Tx and Rx tuned properly the notch depth will approach 65dB.
7.2 400-470 MHZ DUPLEXER TUNING GUIDE
NB: full anti-static precautions are to be taken.
7.3 400MHZ INTERNAL DUPLEXERS
The 400MHz duplexers are band pass duplexers with notches on each of the alternate signal paths. The transmitter
path will have a notch tuned to the receiver frequency. The receiver path will have a notch tuned to the transmitter
frequency. Each of these Duplexers is made up of ten tuneable elements, five for the transmitter path and five for
the receiver path.
Top View of Channel 1 Duplexer
Channel 2 duplexers are electrically identical, however, from the top view they are considered almost symmetrical
about the longest axis. The duplexers are mounted to pillars in the radio housing. M3x10mm T10 Torx head Taptite
screws are used to secure the duplexer. The duplexer is further secured through fixing the N-Type connector to
the front face of the chassis using the N-Type 19mm hex mounting nut and spring washer.