Desensitization Test In Service Duplexer - Motorola R-2200 Operator's Manual

2. Set the "Function" switch to "Pwr Mon/ Anlzr
On" and attenuator to -30 dB. Verify that the
display's center frequency reads the same as the
transmit frequency in step A-7 above.
3. Key the transmitter and adjust the reject notch
adjustments on the duplexer receiver leg cavities
for minimum signal on the display. Change the
attenuator, as necessary, to keep the signal on the
display.
4. Loosen the cavity reject adjustment nut and slide
it within its slot while watching the display.
Tighten the adjustment nut. Be careful not to
mistune the rejection adjustment. Fine tune the
rejection adjustment by turning the bandpass
knob a maximum of +/-15 degrees. This com-
pletes the duplexer receiver leg reject notch ad-
justment.
~
r---1
o-~,·~
.........
0
Rf o./Out
~..=/ Ext-
Domod Out
0 0 0
5llllt1POWOILOAD
Hod Otrt Ext Hod k-1
0 0
\ !
RE.ECT
FIGURE 5.13-DUPLEXER ADJUSTMENT SETUP;
REJECT NOTCH ON TRANSMIT LEG
5.16.0 CAVITY & DUPLEXER TUNING
BANDPASS WITH REJECT NOTCH
C. Adjustment of Reject Notch on Transmit Leg
1. Connect the service monitor's "RF In/Out" to the
in-service duplexer as shown in figure 5.13. Dis-
connect the cable at the duplexer transmitter port
that comes from the transmitter. Move the serv-
ice monitor's "RF In/Out" cable from the
duplexer receiver port to the duplexer transmis-
sion port. Reconnect the cable coming from the
receiver to the duplexer receiver port. Disable the
receiver PL.
2. Set "Function" switch to "Gen", "FM", and enter
the receiver frequency.
3. Set the attenuator to -30 dB and the "RF
Vernier" to mid-range, to allow adequate signal
to get through the duplexer and quiet the re-
ceiver. Reduce the signal generator output, as
necessary, to keep the receiver limiter meter
below saturation.
4. Adjust the reject notch adjustments on the
duplexer transmit leg cavities for minimum signal
level on the receiver limiter meter. Change the
signal generator output, as necessary, to keep the
received signal up out of the noise and below
saturation.
5. Loosen the cavity reject adjustment nut and slide
it within its slot while watching the meter.
Tighten the adjustment nut. Be careful not to
mistune the rejection adjustment. Fine-tune the
reject notch adjustment by turning the bandpass
knob a maximum of
+
/-15 degrees.
6. Remove the test equipment and connect the
duplexer back to the repeater. Check the du-
plexer for insertion loss according to its specifica-
tions .
~
D o.v~
Nrtonno
0
v.rt/SrtN>/
Rf In/Out
DistiDYM
Ext Horiz Domod Out Hod Out Ext Hod In
0 0 0 0 0
REJECT
FIGURE 5.14-DESENSITIZATION TEST SETUP
5.17.0 DESENSITIZATION TEST IN SERVICE
DUPLEXER
5-9
Perform this test after retuning a duplexer or after
detecting inadequate isolation between transmitter and
receiver. The following conditions may make a duplexer
appear mistuned:
High VSWR antenna
IM (intermodulation) between repeater's transmit-
ter and an external signal
Faulty cables or connectors
Improper cable length or configuration