The Front End:
The front end normally designates every-
thing up to the first IF stage, usually the RF
amplifier, oscillator and mixer. The SW-717
has no RF amplifier. The input from the an-
tenna is coupled by separate LC circuits for
bands ‘B’ through ‘D’ directly to the mixer
Q2. Band ‘A’, the broadcast band, uses the
tuned ferrite rod antenna as its coil and is
not connected to the external antenna con-
nector. The mixer incorporates an RCA
40673 dual-gate MOSFET.
The HF oscillator Q1 uses a Motorola
MPF-105 JFET. Power to the oscillator is
regulated by a zener diode for added stabili-
ty. The IF operates at the standard 455 KHz
and the oscillator operates above the re-
ceived frequency on bands A, B and C and
below it on band D. The bandspread only ad-
justs the oscillator frequency. This is also
true on the GR-78 and means as the band-
spread is tuned the input coils are not also
tuned resulting in some minor loss of sensi-
tivity. The oscillator signal is coupled to the
second gate of the mixer MOSFET.
The I-F:
The signal from the mixer is fed through two
455 KHz ceramic filters in series before being
coupled to a 2N5308 high gain Darlington
transistor (Q3). A small un-bypassed emitter
resistor provides some degenerative feedback
for stability. The output of Q3 is coupled to
Q4, a conventional 2N5232A transistor which
provides additional I-F gain and impedance
matching to a third ceramic filter. Output
from the I-F after the filter is fed to the detec-
tor stage and also to the AGC amplifier.
The BFO:
The SW-717 uses an unconventional BFO
circuit. This was probably done as a cost sav-
ings measure. Output from the third IF filter
is fed back through a potentiometer desig-
nated BFO to the input of the input of the
first ceramic filter. In AM the BFO control is
set to zero; in CW the BFO control is ad-
vanced and the I-F starts to oscillate at the
455 KHz frequency of the filters. the level of
oscillation can be adjusted by the BFO con-
trol; however, to change the tone you have to
Frequency Coverage:!
Band A 550 kHz to 1500 kHz!
Band B 1.5 MHz to 4 MHz!
Band C 4 MHz to 10 MHz!
Band D 10 MHz to 30 MHz
S-Meter: Indicates relative signal !
strength.
Headphone Jack: Low impedance head-!
phones or external !
speaker.
Loudspeaker: Built in.
Controls:!
VOLUME with on-off switch.!
MODE AM, Standby and CW.!
MAIN TUNING!
BANDSPREAD TUNING!
ANL ON - OFF (On rear panel)
Transistor Complement:!
40673 (RCA) Mixer!
MPF105 (Motorola) HF Oscillator!
2N5308 I-F Amplifier!
2N5232A (Qty: 2) I-F and AGC Amplifiers!
2N3393 Audio Preamplifier!
X29A829 (GE) Audio Driver!
MPSU05 (Motorola) Audio Output (NPN)!
MPSU55 (Motorola) Audio Output (PNP)
Power Supply: Transformer operated.!
Full-wave bridge rectifier.
Power Requirements: 120 or 240 VAC 50/60 Hz!
8 watts (3/4 amp fused).
Dimensions: 14-1/2”W x 5-3/4”H x 10”D
Net Weight: 7 lbs.
TABLE II :SW-717 SPECIFICATIONS
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