Maintenance, Isolators – Bird Technologies 73-67-25 Series User Manual
Page 27
TX RX Systems Inc. Manual 7-9120-5 07/26/10 Page 21
necessary to rotate the loop for a notch depth
that is slightly less than the reference. The
Notch depth will tend to increase slightly as all
three locking screws are tightened.
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 transmit combiners are com-
posed of passive components, they will continue to
operate without any maintenance for years and
there is no recommended maintenance period.
However, we do feel that it is wise to check com-
biner performance by measuring channel loss peri-
odically and this may be done at any convenient
time along with other radio system maintenance.
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
73-67-11/25-XX-NN series of T-pass transmit com-
biners 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.