Brief Technical Description
15
9. Frequency drift of VFO-1 within the limits of the 37
.
5 Mc/s filter bandwidth, does
not affect the frequency stability of the receiver. A change in this oscillator frequency
will alter the first I.F. to the same extent and in the same sense as the nominal
37
.
5 Mc/s signal from the harmonic mixer. Therefore the difference frequency from
M2 will remain constant.
THIRD MIXER
10. The 2 – 3 Mc/s receiver, which follows M2, is preceded by a pre-tuned bandpass filter.
The 2 – 3 Mc/s output from the filter is mixed in the third mixer with either the output
from the second variable frequency oscillator VFO-2 or an external signal within the
frequency range of 3.6 to 4.6 Mc/s to provide the third intermediate frequency of 1.6
Mc/s.
FOURTH MIXER
11. The 1.6 Mc/s intermediate frequency is mixed in the fourth mixer (M4) with the
1.7 Mc/s output from the 1.7 Mc/s oscillator/amplifier to provide the fourth and final
intermediate frequency of 100 kc/s.
FOURTH I.F. STAGE
12. The final I.F. stages are preceded by crystal lattice and L-C filters which provide six
alternative bandwidths. Separate signal and A.V.C. diodes are employed and alterna-
tive switched time-constants give the optimum conditions for telegraphy and telephony
reception. An additional I.F. amplifier is incorporated to give an independent output
at 100 kc/s.
A.F. STAGES
13. Two independent audio frequency stages are incorporated for either line output or
headphone sockets and internal loudspeaker; each stage is provided with a level control
(see TECHNICAL SPECIFICATION).
CRYSTAL CALIBRATOR
14. A crystal calibrator unit is incorporated to enable the scale of VFO-2 to be checked at
100 kc/s intervals when the V.F.O. switch is set to INT. position. These check points
are obtained from a regenerative divider controlled by the 1 Mc/s crystal oscillator.
Summary of Contents for RA-117
Page 1: ...Racal RA 117 Radio Receiver...
Page 24: ...Detailed Circuit Description 24 at maximum is the correct calibration maintained...
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