Small Wonder Labs PSK-30

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Small Wonder Labs PSK-30 Transceiver Kit 03/09/10 2000 1

PSK-30 Transceiver

Board Kit Instructions

Thanks for purchasing one of the Small Wonder Labs "PSK-30" transceiver kits!

Please take a few moments to look over the sections entitled "First Things First" and "Building Instructions"

before you dive in. These sections contain information which is key to your success with this kit

Note: This version of the printed-circuit board features all through-hole capacitors and only one SMT part

(U8). Please refer to the enclosed sketch for placement of .01 disk capacitors and IC sockets for U3 and U7 and

install those components during assembly. The parts list has been revised to reflect this change.

TABLE OF CONTENTS:

First Things First..................................... 2

Materials ................................................... 3

Parts List ................................................... 4

Theory of Operation ........................... 6

Schematics ................................................. 8

Pictorial Drawing................................... 10

Building instructions , general..........11

Grouped assy. Instr……. 12

"Hooking Up" ................................ 22

Alignment ................................................ 23

Troubleshooting the "PSK-30 " ............... 25

Appendix 1: "Frequently Asked Questions"………26

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The Small Wonder Labs PSK-30 Transceiver Kit is a single PC-board design, measuring 4.6" x 5.27" (7 x 10 cm). It functions as a crystal-controlled SSB transceiver with slightly wider-than-normal IF passband characteristics, covering the frequency range of approximately 10.138 to 10.141 MHz. This manual provides comprehensive instructions for assembling, aligning, and troubleshooting the kit.

Important Technical Specifications:

Power Requirements: The PSK-30 operates with a minimum supply voltage of approximately 10V DC. A power supply capable of delivering a minimum of 1 Amp at 12-14 Volts DC is recommended, with a maximum recommended supply voltage of 15VDC. A suggested low-cost supply is Jameco's #169391, a 15V 1A regulated wall-wart.
Receiver RF Input: 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 preamplifier stage (Q1). The output of this preamp is slug-tuned via inductor L3.
Mixers: Diode-ring Mixer U1 is fed with a 6.1 MHz Local Oscillator (LO) signal, converting the incoming 10.1 MHz received signal to a 4.00 MHz Intermediate Frequency (IF). Q2 and associated circuitry act as a mixer post-amp, providing gain and termination. Product detector U3 receives the 4 MHz IF amplifier output and multiplies it with a 4 MHz LO signal (from schematic point 'E'), resulting in an audio output at pin 5.
IF Filter: The IF filter (Y1-Y4 and associated capacitors) has a 3-dB bandwidth of approximately 2.8 KHz and a loss under 2 dB. Its output is terminated by R12 (4.7K) and U2's input resistance.
IF Amplifier: IF amplifier U2 provides about 30 dB of gain and serves as the control point for the AGC function.
Audio Amplification: Op-amp U4-B and associated components provide audio amplification with a gain of approximately 50 (34 dB) and additional lowpass audio filtering. The output is attenuated by R19 and R20 to a "soundcard-friendly" level.
T-R Switching: Controlled by dual comparator U5 and associated components, T-R switching uses the 'RTS' or 'DTR' signal from the host computer's serial port. MOSFET Q12 shorts the receiver output to ground during transmit, muting it. Comparator section U4-B turns on the transmitter bias switching (Vsw) a few milliseconds later, eliminating transients.
Transmitter Stages: Q6 is an emitter follower providing a 51-ohm source termination for diode-ring mixer U6. U6 is driven by a 4 MHz LO signal from Colpitts oscillator Q7. The output of mixer U6 is a suppressed-carrier double-sideband signal, which, after passing through the transmit IF filter (Y7-Y10), becomes a 4 MHz SSB signal. U7 is an active mixer fed by the 4 MHz SSB signal and a 6.1 MHz LO signal from Colpitts oscillator Q8. Q9 is an emitter follower buffering the mixer's high-impedance output. U8 (Monolithic Microwave IC - MMIC) provides approximately 12 dB of gain.
Bandpass Filtering: L8, L9, and associated capacitors form a bandpass filter with input and output impedances of 50 ohms, cleaning up the mixer U7 output spectrum.
Driver Stage: Q10 and associated components form the transmitter's driver stage, feedback-controlled by R50 for linearity, operating in class-A. The output is L-network matched via L10 and C38 to the Power Amplifier (PA) base. D11 biases the PA base.
PA Stage: Q11 features a bifilar transformer (T2) at its collector, providing a 1:4 impedance match. L11-L13 and C40-C43 form a 7-pole lowpass filter to remove harmonic content, complying with FCC requirements for spurious emissions (all harmonics down at least 50 dB, largest spurious output down 41 dB).
Output Indicator: Diodes D13, D14, and associated components form a peak detector circuit for RF output indication. A 'T1-3/4' LED can be installed at TP2 as a modulation indicator.

Usage Features:

Assembly Sequence: The manual specifies a recommended assembly sequence, but notes that the order of populating the board is not strictly rigid. Some parts are best installed in a particular order, as noted within each group's instructions.
Component Handling: Static-sensitive components (noted in bold) should be kept in their antistatic bag until ready for installation. A grounded-tip iron is recommended, or the iron tip should be touched to shack ground or a PC-board ground point before soldering. Avoid placing these components on paper.
Diode and Resistor Installation: Diodes may be bent for "upright" installation, with the banded (cathode) end oriented at the top, matching the silkscreened circle. Resistors are often installed in "hairpin" fashion, matching the mounting orientation shown in the drawing for better troubleshooting access. Orientation of color bands on nonpolar devices is not critical.
IC Socket Installation: The "notch" or dot at one end of IC sockets should be oriented as shown in the pictorial drawings. Solder two opposite corners first, then reheat while pressing the socket from underneath to ensure it is well-seated.
Toroid Winding: Instructions for winding toroids emphasize counting turns accurately, ensuring snug and uniform windings, and stripping insulation from lead ends. For T2, specific instructions are given for winding a bifilar pair without twists.
Alignment:
- Receiver Alignment: Involves connecting the soundcard to the PSK-30, downloading DigiPan software, adjusting trimmer capacitor C44 to center the noise picture, and adjusting inductor L3 for maximum audio with an antenna connected.
- Frequency Alignment: Requires transmitting a CW signal on 10140.0 MHz (into a dummy load) and adjusting C48 to align the signal line with the '10140' tick mark on DigiPan.
- Transmitter Alignment: Involves connecting the serial port cable and a dummy load, setting DigiPan's 'Transmitter drive' levels, verifying TX bias voltage at Q10, and adjusting inductors L8 and L9 for maximum meter indication (or maximum output on a wattmeter).
- Operational Adjustment: For wattmeter users, adjust the master volume slider for 3 Watts output in 'TUNE' mode. For those without a wattmeter, install an LED at TP2 and adjust the master volume slider until the LED glows steadily and flickers brighter when typing. Oscilloscope users can adjust output envelope just below distortion.
Enclosure: The board can be mounted in an enclosure using #4 machine screw hardware and #4 spacers. Information on a specific Lansing 'Micropak' CT1-series enclosure with a custom-punched end panel is provided.

Maintenance Features:

Troubleshooting: The manual emphasizes checking for solder bridges, missing solder joints, and incorrect component installation (ICs, transistors, diodes). It notes that most problems are due to cold solder joints (85%), solder bridges (5%), or incorrect resistor installation (5%).
Desoldering: Recommends using desoldering braid to remove components. For transistors, it suggests snipping the part off and pulling leads out singly to minimize pad damage.
Component Removal: If a through-hole is blocked with solder after component removal, a dissecting needle, dental probe, or wooden toothpick can be used with heat to clear it.
Cleaning: After assembly, use cotton swabs and acetone (nail polish remover) to remove solder flux from the underside of the PC board. Caution is advised to avoid getting acetone on plastic items on the top side.
Technical Support: Contact information for Dave Benson, NN1G, is provided for further technical support. Troubleshooting services are available for a flat fee.