Introduction

First stage is the power supply. The circuit has 2 power rails:
  • 12 Vdc power (for the transmitter)
  • and 5 Vdc power (for LO and ICs)
Things to watch out for in this stage are:
  • Ensuring the electrolytic caps are mounted correctly with respect to polarity. The positive lead is the longest lead; the negative lead is identified by a grey marking on the "-" side of the can.
  • Mounting the diode D1 corretly with respect to polarity.  The anode end (no marking) should be installed snug to the round pad and the cathode end (identified by a band) mounted "hairpin" style into the square pad (see the topside illustration below).
  • Soldering the leads on the 5 volt regulator, U4.  U4 is mounted to conform to the shape on the board silkscreen,  After soldering the leads, double check them for solder bridges.
If this is your first time dealing with SMT components, check out the online primer on soldering SMT components.

Schematic

Power Supply Schematic

Bill of Materials

Designation Value Orientation Notes
C25 10uF/16 VDC Electrolytic South-North
C26 10uF/16 VDC Electrolytic South-North
C27 10uF/16 VDC Electrolytic East-West
C28 10uF/16 VDC Electrolytic East-West
C29 10uF/16 VDC Electrolytic North-South
C30 10uF/16 VDC Electrolytic North-South
C31 10uF/16 VDC Electrolytic North-South
C32 10uF/16 VDC Electrolytic North-South
C33 10uF/16 VDC Electrolytic North-South
C34 10uF/16 VDC Electrolytic North-South
C35 10uF/16 VDC Electrolytic South-North
C63 0.1uF smt 1206 smt
C64 0.1uF smt 1206 smt
C65 0.1uF smt 1206 smt
D1 1N4003 East-West Mount the diode D1 correctly with respect to polarity.  The anode end (no marking) should be installed snug to the round pad and the cathode end (identified by a band) mounted "hairpin" style into the square pad
R44 49.9, 1/4W, 1% South-North
U04 78L05, 5v voltage regulator TO 92

Build Notes

Power Supply Board Topside

Power Supply Bottomside

JP1

Mount a small (sturdy) wire loop in hole 4 of JP1 location to use as a ground test point. A short length of resistor or capacitor lead may be used for each of the wire loops. Make it stout - you will really use and abuse this lead during testing.

JP1 Loop

Testing

Current Draw

  • Initially, place a current limiting 1K resistor in series with one of the power leads,
  • apply 12 Vdc power
  • measure the current draw.
  • You should see less than 10 mA draw. If the draw is greater than 10 mA, you should check your circuit for a short.
  • Remove the current limiting resistor
  • apply 12 Vdc power
  • measure the current draw.
  • The result should be around 4.5 mA. Much greater than that and you should look for an electrolytic capacitor with the wrong polarity.
  • Set the ammeter back to voltage

Voltages

  • Set the DMM to voltage
  • apply 12 Vdc power to the board
  • Measure the voltage at the point on the board marked "+5V"
  • You should see a value in the range of 4.75 volts to 5.25 volts (i.e., +/- 5%).