TR-800 Service Manual
63
Duplexer Instructions
Electrically, a duplexer is a device using sharply tuned resonate circuits to isolate a transmitter from a
receiver. This allows both of them to operate with the same antenna at the same time without the
transmitter RF frying the receiver. Please check the duplexer is tuned to the correct operating
frequencies before using the repeater. You can tune the duplexer using one of the following three
methods:
z
Pre-Tuned Method (preferred method)
Order the duplexer pre-tuned to the desired frequencies from the manufacturer or supplier. This is not a
“method” of tuning the duplexer and does not require any field tuning or test equipment. Note that there
must be certain frequency spacing between the Tx and Rx frequencies. This is called “spacing”. For 2m
wavelength, the spacing is about 600 KHz. For 70cm wavelength, the spacing is 5MHz (duplexers with
such spacing can be realized more easily).
z
Visual Method
Use a tracking (sweep) generator and spectrum analyzer to adjust the pass-band and reject-band
specifications of the duplexer.
z
Emergency Method
The following paragraphs address a simple method to tune a “notched” duplexer such as DT04 UHF
duplexer. This method is not as accurate as the visual method provided by the tracking generator
/spectrum analyzer sweep setup but it is much less costly. It may be sufficiently good for all but the most
exacting applications.
Use this method only when the operating frequencies of the master radio and slave radio meet the
requirements of duplexer. The duplexer you can order from HYT is a notched type (band-reject) only.
The minimum spacing available is 4MHz for UHF band and 3.5MHz for VHF band. Note that this notched
type duplexer offers a considerably narrow bandwidth. If the operating Tx/Rx frequencies for TR-800 are
appreciably different from that of the duplexer, degraded performance of the repeater will result.
The following procedure assumes that the duplexer is applied and the radios should be connected to the
proper ports of the duplexer with the RF coaxial cables provided in the TR-800 kit. The duplexer should
not be mounted on the bracket and the tuning screws of the duplexer (on the other side of the cavities,
opposite to the RF connectors) should be accessible.
Programming the Radios
1. Program the master radio to the “Rx=Tx” mode at the frequency of Receive (assuming that the
master radio operates as transmitter of a uni-directional repeater).
2. Program the slave radio to the “Rx=Tx” mode at the frequency of Transmit (assuming that the slave
radio operates as receiver of a uni-directional repeater).
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