Manual

TXRX Systems Inc. Manual 7-9176-4 06/23/04 Page 1
GENERAL DESCRIPTION
Vari-Notch® duplexers are used to provide simulta-
neous operation of a transmitter and receiver (or
two transmitters) which are at different frequencies
while connected to a common antenna. These
duplexers are frequently used in radio repeater
systems. This instruction manual (part# 7-9176-1)
covers the installation, tuning, and maintenance of
Vari-Notch duplexers constructed from 4” diameter
cavities.
Tabl e 1
shows the model numbers and
electrical specifications of the duplexers covered by
this manual. Vari-Notch duplexers are composed of
two groups (or sets) of daisy-chained resonant cav-
ity filters, which couple signals to and from the
shared antenna. This creates two signal paths, a
high frequency channel and a low frequency chan-
nel. The minimum frequency separation between
the channels, as well as the isolation in dB’s (per
channel and between channels) is listed for each
model in table 1.
The cavity filters used in a transmit channel will
reduce transmitter noise components at the
receive frequency, thus preventing noise desensiti-
zation of the receiver. Conversely, the cavity filters
used in a receive channel will isolate the receiver
from the transmitter carrier preventing carrier
desensitization of the receiver.
Model
Number
Frequency
Range
(MHz)
Power
Rating
(Watts)
Min. Freq.
Separation
(MHz)
Insertion
Loss
(dB)
Isolation
(dB)
Per Chan. Bet Chan
28-38-03A/D 132 - 174 150 0.5 1.9 80 45
28-37-07A/C 144 - 174 400 3 0.7 85 30
28-37-06A/C 144 - 174 125 1 1.2 75 35
28-37-04A/C 144 - 174 125 0.5 1.8 65 30
28-37-81227-A-R2 144 - 174 125 0.5 2 65 30
28-52-02A 215 - 250 250 1.6 1.2 90 55
28-56C-02A 380 - 420 250 5 0.7 100 50
28-65-07A/B 406 - 430 250 3 1.25 85 60
28-65-02A/B 406 - 430 350 3 0.8 80 30
28-66-02A/B 442 - 450 350 5 0.6 100 46
28-70-09A/B 450 - 470 250 5 1.25 100 70
28-70-02A/B 450 - 470 350 5 0.6 100 46
28-69-06A/B 470 - 512 250 3 1.25 86 60
28-69-02A/B 470 - 512 350 3 0.8 80 30
28-89-01A/B 806 - 866 125 45 0.8 90 60
28-88-04A/B 890 - 960 125 39 0.8 90 50
28-88-01A/B 890 - 960 125 3.6 1.25 90 40
28-97-01A/B 1215 - 1300 125 12 1 100 50
Tabl e 1:
Vari-Notch Duplexer electrical specifications.