TELE-TECH & - AmericanRadioHistory.Com

Getting back to the front end of
the i -f amplifier, the low -noise preamplifier
uses a type 416B triode in
a grounded -grid circuit. The i -f
noise figure is about 5 db, and the
overall receiver noise figure is
about 19 db. An AFC system is
utilized that is relatively simple
and has proved quite effective. This
is a dual -channel system, in which
two narrow -band i -f amplifier channels
are used, each with a bandwidth
of 10 MC. One of these channels
is tuned to 20 MC below the
center frequency of the i -f amplifier,
and the other is tuned 20 MC
above the center frequency. These
amplifiers effectively sample the
energy content of the spectrum of
the i -f pulse on either side of its
peak. When the receiver is properly
tuned, the i -f spectrum will
produce equal outputs in the two
channels. Any unbalance in the
outputs of the two channels signifies
improper tuning. This unbalance
is detected and used to correct
the local -oscillator tuning.
The remainder of the receiver
contains a distributed detector,
video amplifier and line drivers,
gain control circuits, and a sensitivity-
time -control circuit.
In the PPI, a special 16 -inch
cathode -ray tube preserves the
high -resolution capabilities of the
system. Although the tube has no
unusual or unique characteristics,
it does represent a combination of
the best known techniques to give
high resolution for this application.
The resolution obtainable is better
than 1000 lines /diameter.
Instead of the usual servo system
to drive the rotating deflection
yoke in step with the antenna, a
simplified synchronous motor drive
system has been devised. In this
system, an alternator is geared to
the antenna at about 80 times the
speed of the antenna. The 80 -cycle
voltage from the alternator is used,
after amplification, to excite a synchronous
motor in the PPI that
drives the deflection yoke through
a corresponding gear train. The
system is designed to hold the deflection
yoke within -±-0.1 degree
of the relative position of the antenna
and hold this accuracy in the
face of the greatest accelerations
to be expected from the antenna.
This system has many possible
(Continued on page 186)
RCA "Time- Proved" Tube Designs
...for longer life
The remarkable endurance of RCA Power Tubes in radio
communications is due in great measure to RCA "proved -in"
designs that have stood up in practical transmitter operation
over many years. They are your answer to lower tube costs per
hour of operation.
For prompt service on RCA Tubes, .contact any RCA Tube
Distributor (located in all major cities). Tube technical data on
mobile communication types can be obtained from RCA, Commerical
Engineering, Section HOP. Harrison, N. J.
TUBES for COMMUNICATION
Radio Corporation of America Harrison, N. J,
Tele -Tech & ELECTRONIC INDUSTRIES June 1956
For product information, use inquiry cord on pages 209 -210. 185