Radar System Engineering

432 R-F COMPONENTS [SEC.1112
the receiver sensitivity y. In the radar operating position a straight piece
of waveguide with a choke-flange joint at each end transmits the power
direct to the antenna. There is, of course, appreciable r-f leakage at the
air gaps of the two junctions. Accurate construction keeps this small
enough not to affect the AFC mixer in the same compartment. A safety
switch prevents turning on the magnetron unless the guide is in proper
position. This piece slides out of the way and a matched probe-fed
transition piece slides in for introducing a test signal.
The receivers are typical of ground and ship sets, except that in this
case they do not contain the regulated power supplies. The usual i-f and
video amplifier, the various anti clutter circuits, and the .4FC circuits are
included. A tight outer box provides general shielding, but the i-f
amplifier and local oscillator have inner shields in addition.
One of the most noteworthy features of this radar is the built-in
test equipment. An operator can go to the turret and, by transferring
the usual remote controls to a duplicate set in the turret, operate the
radar and view the echoes or waveforms on the scope provided. A universal
meter furnishes a quick check on all the currents mentioned in
Sec. 11.11. The vital check on receiver sensitivityy is made with a
klystron noise source, whose output signal is introduced via the r-f
switch just described. The reliability and day-to-day reproducibility
of the test set are excellent, and having it built in makes a quick daily
check on a cent inuousl y operated radar simple to perform. Over-all
noise figures of 9 to 12 db are commonly maintained.
Neither the r-f head nor the waveguide is pressurized. The moisture
problem in the turret is solved by electric heaters which come on whenever
the radar shuts down. Only a few degrees rise above general
atmosphere temperature prevents condensation. Drain holes for water
are provided at proper points in the antenna line.