total of 1.5 dB of insertion loss. The total insertion
loss is the sum of losses from each cavity in the
channel as well as from the interconnecting cables
between the cavities.
Required Equipment
Due to the sensitivity of the adjustments, it is
strongly recommended that the proper equipment
be used when tuning the individual filters, other-
wise the filter should be sent to the factory or an
authorized representative for retuning. The follow-
ing equipment or it's equivalent is recommended in
order to properly perform the tuning adjustments
for the Vari-Notch duplexer.
1. IFR A-7550 spectrum analyzer with optional
tracking generator installed.
2. 5/32" hex wrench.
3. Double shielded coaxial cable test leads
(RG142 B/U or RG223/U).
4. 50 ohm load with at least -35 dB return loss
(1.10:1 VSWR). The JFW Industries model
50T-007 or equivalent.
5. Female union (UG29-N or UG914-BNC).
6. Return Loss Bridge
(Eagle model# RLB150N3A).
7. Insulated tuning tool (TX RX Systems Inc.
part# 95-00-01).
Tuning Procedure
Tuning of the filter requires adjustment of the
passband and the rejection notch. The passband
is adjusted while observing the return loss re-
sponse and the rejection notch is adjusted by
monitoring the output of a tracking generator after
it passes through the filter.
All Vari-Notch filters should be temporarily re-
moved from the system and tuned on the bench
using test instrumentation only. Do not adjust the
filters while they are under transmit power. To in-
sure proper tuning of the 6.625" Vari-Notch filter,
all adjustments should be performed in the follow-
ing order:
1. Rough tune the passband.
2. Rough tune the rejection notch.
3. Final tune the passband.
4. Final tune the rejection notch, always the last
adjustment made.
WARNING - Tuning while under trans-
mit power can result in damage to the
duplexer.
PASSBAND
The peak of the passband will correspond very
closely to the point of minimum reflected energy
from the filter and maximum forward power
through it. A transmitter connected to the filter will
operate best when the reflected energy is lowest,
therefore the return loss response will be used to
set the passband. The passband can be checked
and adjusted using the following procedure.
Checking the passband
1. A zero reference for return loss must be estab-
lished at the IFR A-7550 prior to checking the
passband frequency, this is done by connect-
ing the return loss bridge to the analyzer / gen-
erator as shown in figure 3.
TX RX Systems Inc. Manual 7-9177-1 09/19/97 Page 4
GENERATE
OUTPUT
ANALYZER
INPUT
40
30
20
10
0
-10
-20
-30
-40
dBm
40
0
10
300
dB ATT
GEN
dBM
MSEC
KHz RES
KHz/DIV
200
MHz
LOAD
SOURC
E
REFL
ECTED
RLB - 150 BRIDGE
Figure 3: Setting the return loss reference.
