Recent Performance and Operational Reports indicate several equipment failures that have been attributed to improper operation or installations. It is important to tune the AN/SRA-22 with only TUNE power applied from the associated radio set AN/URC-32 (tune switch is located on the power amplifier chassis), otherwise a badly detuned antenna can cause damage to the coupler unit if full power is applied.
Additionally, the AN/SRA-22 antenna coupler control unit contains a SERIES-SHUNT and CAPACITOR switch that must be operated in accordance with the instructions in the technical manual (or on the associated Operating Instructions Chart). Steps should be followed in that definite discreet sequence and this switch should not be moved again until the red light on the panel indicates the variable capacitor of the coupler has stopped moving as indicated by the red light being extinguished. On certain frequencies and when working into a whip antenna, if the switch is moved more than one step at a time, a radical large change in Q is possible so that exceptionally high voltages can develop within the coupler to cause a voltage breakdown.
Additional difficulties reported indicate that improper antenna tuning is caused by a dirty antenna base insulator, leaky coaxial cable transmission line to the coupler, or inadequate coupler unit grounding. Periodic inspection and cleaning of the antenna base insulator, "megger” checks of the transmission line, and verification of a good ground connection to the coupler CU-714/SRA-22 case will reduce these failures. Do not rely on a good ground being provided by the bolts attaching the coupler to its mounting; a separate ground strap is mandatory.
The Bureau is currently investigating a satisfactory equipment field change for the reduction of equipment failures due to operator mistuning, and the inclusion of a high VSWR protective circuit
C-2698/SRA-22 coupler control
or C-2494/SRA-22 coupler control
manuf Collins 180R-6
