By David Cameron VE7LTD

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1 By David Cameron VE7LTD

2 Introduction to Speaker RF Cavity Filter Types Why Does a Repeater Need a Duplexer Types of Duplexers Hybrid Pass/Reject Duplexer Detail Finding a Duplexer for Ham Use Questions?

3 Not an expert in RF, just a hobbyist Basic/Advanced licensed since 1993, through UBC ARS Born, raised, and living on the North Shore Designed and rebuilt the current UBC Ham repeaters (VHF, 220, UHF) Designed and maintain the IRLP System

4 Started with duplexers after seeing several cavities laying around UBC club Borrowed a few, and using a handheld and a power meter learned how they work

5 Bandpass Filter Passes only selected frequency, attenuates others. Notch Filter Passes all but selected frequency. Hybrid Pass / Variable Notch Filter Passes selected frequency, notches a different selected frequency.

6 Has two ports (input and output). The pass loss through the cavity is adjustable. The higher the pass loss, the higher the rejection outside the pass. Using multiple low-loss cavities in series is better than increasing the loss on one.

10 Has a single port with either a fixed or variable capacitor. The notch is adjusted by moving the tuning rod inside the cavity. Notch filters pass all frequencies except the desired notch frequency.

11 Has a single port with a variable capacitor. Contains characteristics of both bandpass and notch filters in one cavity. Pass loss and notch depth are adjusted by changing the orientation of the coupling loop.

14 High powered transmitters and sensitive receivers don t mix well: Example: Desense effect of handheld beside a mobile transmitter on the same band. Transmitters put out low levels of wideband noise that can be on the receive frequency. High levels of received signals on nearby frequencies cause intermod.

15 Couples both receiver and transmitter into one antenna Requires only one antenna Requires only one feedline Two antennas are a possibility, but require vertical separation to work On VHF, a 10 watt transmitter would require over 100ft. On UHF, a 10 watt transmitter would require about 40ft.

16 One port connects to the antenna. One port connects to the transmitter (TX). One port connects to the receiver (RX). The TX port passes the TX frequency while notching out the RX frequency: Prevents any wideband noise from the TX being received by the RX. The RX port passes the RX frequency while notching out the TX frequency: Prevents any power from the TX from entering the RX.

17 A duplexer is a series of cavites chained together to isolate two radio devices from one another. Could be a receiver and a transmitter, two transmitters, or two receivers. Duplexers which have a relatively small separation of frequencies are build using hybrid pass/notch filters, or notch only filters. Duplexers which have a larger separation can use bandpass filters.

18 Advantages: High power handling Prevent all out of band signals from reaching the receiver By design, filter out a lot of spurious transmissions from the transmitter. Disadvantages High insertion loss ~ 3db Can only be used where there is a large separation between frequencies (only on 440Mhz and above)

19 Advantages: Can be used in mobile applications Small footprint can fit inside a radio Can be used on a wide range of frequencies Inexpensive Disadvantages Low power handling 50 watts maximum High insertion loss ~ 2db Can only be used where there is a large separation between frequencies (only on 440Mhz and above) Allow all out of band frequencies to pass.

20 Advantages: Can isolate receiver and transmitter on close separations (>500Khz) Low insertion loss ~1.5db High power handling ~250W Disadvantages Allow all out of band frequencies to pass, although in-band signals are slightly attenuated. Popular on the used market, and therefore expensive.

25 144 MHz (600 khz) 220 MHz (1.6 Mhz) 440 MHz (5 Mhz) Bandpass NO MAYBE YES Notch NO MAYBE YES Hybrid Pass/Notch YES YES YES

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