Bird Technologies 21-87A-11-xx-T Series-Manual - Manual (Page 29)

TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 23
11) Tighten all loop locking screws. The cavity loss
is now set. The cavity will have to be tuned to
its operating frequency following the proce-
dures outlined earlier in this manual.
MAINTENANCE
Because T-Pass transmitter multicouplers are
composed of mostly passive components, they will
continue to operate without any maintenance for
years and there is no recommended maintenance
period. We do feel, however, that it is wise to check
multicoupler performance by measuring channel
loss periodically and this may be done at any con-
venient time along with other radio system mainte-
nance.
ISOLATORS
Isolators perform two important functions. Their pri-
mary function is to keep unwanted RF frequencies
out of the transmitter so that intermodulation prod-
ucts cannot be generated. Isolators have a sub-
stantial amount of reverse isolation. They also
ensure that the transmitter never sees any signifi-
cant reflected power so it will always operate with
maximum stability at full-power output. Isolators
prevent energy from getting into the transmitters
output by dumping any RF energy entering the out-
put of the isolator into a dummy load. The model
73-90-11 series of T-pass transmit combiners will
use either single section or dual section isolators at
the input to each T-pass channel.
Single-section isolators have one load port. A prop-
erly sized load capable of dissipating the maximum
expected reflected power that might be encoun-
tered should be used. Dual section isolators have
two load ports, one for each section. Although
loads of equal power rating may be used for both
ports, it is customary to use an output load capable
of dissipating the maximum expected reflected
power that might be encountered. A small load (5
watts) is usually factory installed on the first section
of the isolator where high reflected power is not a
factor. Refer to Appendix A for a further discus-
sion of isolators.