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2. Design
The ATmega328 AVR microcontroller (IC1) is pre-programmed with firmware to control the LCD, buttons,
and GPS interface. The Si5351A Synthesiser module kit includes its own on-board 27MHz crystal
reference oscillator. On/off keying is handled in software by switching on/off the output stage of the
Si5351A synthesiser IC. The Q1 BS170 MOSFET is the power amplifier, producing about 250mW from a
5V supply on 30m (power output varies on different bands). Finally standard 7-element low pass filter plug-
in modules remove harmonics of the transmission frequency.
3. Parts List
3.1 Resistors
R1
100K preset potentiometer, for LCD contrast adjustment (code "104")
R2
No resistor – space is provided on the PCB only for reducing LCD backlight brightness
R3
No resistor – space is provided for a 100K resistor, if you want to do AVR firmware upgrades
R4
No resistor – space is provided for a 220K resistor, for smoother contrast adjustment
R5
4.7K preset potentiometer, for setting the PA bias (code "472")
R6
4.7K resistor
3.2 Capacitors
C2, 3
22pF (ceramic, marking 22, or 220)
C1, 4, 5, 6
10nF (ceramic, marking 103)
C7
No capacitor – space is provided for future enhancements
3.3 Inductors
L1
25 turns, FT37-43 core (black)
3.4 Semiconductors
Q1, 2, 3
BS170 (note: two BS170 are provided in the kit. Only one needs to be installed in the kit.
For use with higher PA supply voltages, more transistors may be added, i.e. Q2 and Q3).
D1
No diode - provided for use with relay-switched LPF board kit
IC1
Pre-programmed ATmega328 microcontroller
Si5351A
Synthesiser module, including 27MHz reference oscillator
3.5 Miscellaneous
Two push buttons, S1 and S2
16-column x 2-row LCD (HD44780-compatible) with blue LED backlight
Printed circuit board, 80 x 37mm size
Wire for winding toroid
Socket for IC1
20MHz quartz crystal
Two 10-pin female header sockets
Two 4-pin female header sockets
16-pin female header socket
16-pin male header plug
Four 12mm nylon hex PCB spacers
Eight 6mm M3 screws
Relay RL0 – not supplied, provided for use with relay-switched LPF board kit
3
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