User's Manual

6. ALIGNMENT
6.1 DUPLEXER
The duplexer allows the Repeater to simultaneously transmit and receive. To accomplish this, in the
receive input path, the transmitter signal must be notched or suppressed by 70 dB or more. In addition, on
the transmit path, transmitter noise on the receive frequency must be also suppressed by about 70 dB. The
duplexer contains four cavities, two for each path to achieve the necessary notch depth. Because the
notches are very narrow, the duplexer must be re-tuned if the frequency of operation is changed by more
than 50 kHz. Follow the procedure below to tune the duplexer:
1. Connect the antenna to be used to the antenna connector on the Repeater. If possible, the antenna
should be positioned in a way that matches the actual configuration as close as possible. If the antenna
requires tuning, tune it to the transmit frequency. If an antenna is not available, connect a low VSWR
50-ohm load instead.
2. Unplug the two RF cables connecting the duplexer to the main PCB.
3. A spectrum analyzer with tracking generator or a network analyzer should be used to sweep the
duplexer. If one is not available, a spectrum analyzer and an RF signal generator can be used, but the
notch frequencies will be difficult to determine. The duplexer should be swept from one RCA plug to
the other; it doesn’t matter which end goes to the generator or the spectrum analyzer.
4. One should see at least two, and maybe as many as four notches. Carefully loosen the nuts on the two
duplexer cavities underneath the transmitter portion of the main PCB. Adjust the two cavity screws for
the deepest notch possible at the RECEIVE frequency. Tighten the nuts being careful not to de-tune
the notch frequency. Do the same for the two screws on the cavities underneath the receiver portion of
the main PCB, but tune for a notch at the TRANSMIT frequency. When finished, one should see two
notches, one at the transmit frequency and one at the receive frequency. These two notches are very
narrow and special attention should be paid to ensuring that they are at the correct frequencies. The
two notches should be about 70 dB deep compared to a straight-through connection.
6.2 PRELIMINARY
1. Alignment of the RLR-460 Repeater requires that surface-mount potentiometers be adjusted. These
potentiometers do not have end stops so one must pay special attention to the wiper position for
maximum clockwise and counterclockwise settings. Also, one should be careful never to set the wiper
in the dead band between maximum and minimum.
2. Alignment of the Repeater requires connection to the pins on the front panel modular jack.
3. The frequency deviation numbers shown are for narrow (12.5 kHz channel spacing) operation. Double
the values for wide (25 kHz channel spacing) operation.
4. A communications service monitor capable of duplex operation is required to set R328 (REPEAT
AUDIO LEVEL). Other alignment steps can use individual pieces of equipment (RF signal generator,
RF wattmeter, etc.), although communications service monitors tend to include all the functions
necessary to align this product.
5. Ensure that the Repeater is properly programmed for the correct transmit and receive frequencies and
the correct QC/DQC tones/codes. Even if a transmit tone is not to be used (unusual), one should
program one anyway to get the transmit tone deviation properly set. This parameter is, however, set at
the factory.
6. Refer to the RLR-460 ALIGNMENT POINTS diagram for the location of alignment points and
adjstments.