Small Wonder Labs
PSK-20 Transceiver Kit 03/09/10
2000
6
Parts list (cont'd)
Quantity
Reference Designator
Value
Description
Markings or Ident.
2
U3,U7
SA612AN,
SA602AN
Mixer IC
8-pin DIP pkg
1
U4
LM1458
Dual op-amp IC
8-pin DIP pkg,
'1458, '4558','5558' or
'HA17458'
1
U5
LM393
Dual comparator IC
8-pin DIP pkg
1
U8
MAR-3SM
Microwave IC,
Pre-mounted on
board
1
U9
78L08
Voltage regulator IC
TO-92 pkg.
9
Y1-Y5,Y7-Y10
9.00 Mhz
Crystal (short case)
HC-49/S pkg.
1
Y6
5.068 Mhz
Crystal
HC-49/U pkg.
5
S1-S5
8-pin DIP IC socket
1
4-40 x 1/4" machine screw
1
4-40 Nylon nut
1
HS1
TO-220 heat sink
1
W1
2' (0.7m) power wire
1
P1
2.1/ 5.5mm coaxial plug
1
Telephone wire, 16" (40 cm)
1
Tuning wand, plastic
white
Theory of Operation:
This transceiver is a single PC-board design measuring
4.6" x 5.27" (7 x 10 cm). It is functionally a crystal-
controlled SSB transceiver with slightly wider-than-
normal IF passband characteristics. It covers the range
of 14.069 to 14.073 Mhz.
Note:
Further description of this design is found in the
June 2000 issue of
QST
magazine.
Receiver Operation:
The receiver RF input (schematic point 'D') is applied
through a series-tuned resonant circuit (C1/L1) and
limiter (D1-D4) to a low-gain preamplier stage
comprising Q1 and associated components. The
output of this preamp is slug-tuned via inductor L3.
Diode-ring Mixer U1 is fed with a 5 Mhz Local
Oscillator (LO) signal and converts the incoming 14
Mhz received signal to the 9.00 MHz Intermediate
Frequency (IF). Q2 and associated circuitry are a
mixer post-amp and provide both gain and a
termination for the mixer. The post-amp is followed by
a 6-dB resistive attenuator with two-fold purpose: it
provides a stable load to the post-amp and reduces
filter passband ripple.
Y1-Y4 and associated capacitors are the IF filter. This
filter has a 3-dB bandwidth of approximately 3.5 Khz
and loss under 2 dB. Its output is terminated by R12
(2.2K and U2's input resistance. IF amplifier U2
provides about 30 dB of gain and also serves as the
control point for the AGC function (more on this later).
The IF amplifier output is coupled to the product
detector via T1, a tuned IF transformer.
Product detector U3 receives the 9 Mhz IF amplifier
output and multiplies (mixes) it with a 9 Mhz LO
signal (from schematic point 'E'. This results in an
audio output at pin 5 of that IC. C14 provides rolloff
of the audio to reduce high-frequency 'hiss'. Op-amp
U4-B and associated components provide audio
amplification. This stage has a gain of approximately
50 (34 dB) and provides additional lowpass audio
filtering as well. The output of this stage is
considerably larger than your computer's soundcard
expects to see, and the combination of R19 and R20
attenuates this signal down down a 'soundcard-friendly'
level.
Because the active soundcard inputs are always active,
even during transmit, the receiver must be 'muted'
