User Manual

TR-800 Service Manual
-35-
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 on the same antenna at the same time without the
transmitter RF frying the receiver. Before using your repeater, you must tune the duplexer using one
of the following three methods for ensuring that the duplexer is tuned to the correct frequencies of
operation:
 Pre-Tuned Method (preferred method)
Order the duplexer from the manufacturer or supplier pre-tuned to the desired frequencies. This
is not a “method” of tuning the duplexer but does not require any field tuning or test equipment.
Note that there must be a separation of the transmit and receive frequencies. This is called
“split”. On two meters the split is about 600 KHz. On 70cm the split is much easier to do 5MHz.
 Visual Method
Use a tracking (sweep) generator and spectrum analyzer to adjust the tuning of the pass bands
and reject bands of the duplexer.
 Emergency Method
The following paragraphs address a simple method of tuning a “notched” duplexer such as
DT04 UHF duplexer. This is not as accurate a method of tuning as the visual method afforded
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 main radio and slave radio meet
the requirements of the duplexer. The duplexer you can order from HYT is notched type
(band-reject) only and the minimum separation available is 4MHz on UHF band and 3.5MHz on
VHF band. Note that this notched type duplexer offers a considerably narrow bandwidth. If the
operating transmitter/receiver frequencies for the TR-800 are appreciably different than that of
duplexer specification, 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 main radio with an additional “receive only” mode at the frequency of receive
(assume that the main radio operates as transmitter of a uni-directional repeater).
2. Program the slave radio with an additional “receive only” mode at the frequency of transmit
(assume that the slave radio operates as receiver of a uni-directional repeater).
3. Connect a communications test set, such as HP8921 series, or an RF signal generator to
the antenna port of the duplexer. The test set should be operating in the “Generate” mode.
Modulate the RF source with a 1kHz tone at 60% system deviation to facilitate “hearing”
the signal during the tune-up procedure.
Tuning the Main Radio Section
Tuning the main radio section of the duplexer begins with the tuning screw closest to the antenna
port of the duplexer.