Racal Instruments RA-117 User Manual page 35

(3) Set the controls of the signal generator for a 30% modulated signal of 1 V at 3.5
Mc/s and an impedance of 75 ohms. Connect the signal generator output to the
receiver antenna input socket.
(4) Tune the receiver to the output frequency of the signal generator and adjust A.F.
GAIN control until the output indicates 10mW.
(5) Increase the output of the signal generator to 100mV (+100dB) and check that
the reading on the output meter does not exceed 50mW (+7dB on 10mW).
A.F. LEVEL METER TEST
9. Perform a test of the A.F. LEVEL meter calibration as follows:-
(1) Set the controls of the output meter for an impedance of 600 ohms and a power
range of 120mW. Connect the meter across the 600-ohm 10mW output terminals.
(2) Set the controls of the signal generator for a 30% modulated output of 3.5 Mc/s
at an impedance of 75 ohms and a level of 5 V. Connect the signal generator to
the antenna input socket of the receiver.
(3) Tune the receiver to the output frequency of the signal generator and adjust the
A.F. LEVEL control until the meter reads exactly 10mW. Check that the external
output meter reads within 1dB of 10mW.
NOTE: It is important that the A.F. LEVEL control is not turned towards its maximum
position unless the 10mW 600-ohm winding is suitably terminated with a load.
NOISE FACTOR TEST
10. Perform a noise factor tests as follows:-
(1) Set the receiver controls as detailed below:-
R.F. RANGE
MEGACYCLES
KILOCYCLES
SYSTEM switch
R.F. ATTENUATOR
BANDWIDTH
B.F.O. switch
LIMITER
R.F./I.F. GAIN
B.F.O. NOTE
SPEAKER
(2) Set the noise generator RANGE switch to OFF.
(3) Connect the noise generator output to the receiver antenna input socket.
(4) Set the controls of the output meter for an impedance of 3 ohms and a power
range of 60mW and connect it to the 1W 3-ohm output terminals of the receiver.
(5) Set the A.F. GAIN control for a convenient level and adjust the MEGACYCLES
tuning and R.F. TUNE controls for maximum noise in the loudspeaker.
(6) Adjust the A.F. GAIN control to obtain a reading of approximately 10mW on the
output meter. Check that the MEGACYCLES and R.F. TUNE controls are set
for maximum output and then reset the A.F. GAIN control for exactly 10mW.
General Servicing and Aligment Procedures
16 – 30 Mc/s
29
0
MAN.
MIN.
3 kc/s
ON
OFF
maximum gain position
1 kc/s
ON
35