The second stage is the Local Oscillator. The circuit must provide the clock signal that is 4 times the desired center frequency. In the 40/30m kit, the two output frequencies correspond to the 2 crystals supplied:

  • 40m: 28.06 MHz or 28.224 MHz,respectively, for 7.015 MHz or 7.056 MHz center frequency
  • 30m: 40.5 MHz for the 10.125 MHz center frequency
Things to watch out for in this stage are:
  • Mounting the crystals and attaching their ground straps.
  • Soldering the leads on the transistors, Q13 and Q14.  They are mounted to conform to the shape on the board silkscreen,  After soldering the leads, double check them for solder bridges.


Local Oscillator Schematic

Bill of Materials

C43100pF, ceramic, 5% n/a
C4522pF, ceramic, 5% n/a
C500.1uF, smt 1206 smt
C730.1uF, smt 1206 smt
JP22-pin hdr & jumper plug n/a
Q132N3904 NPN TO 92
Q142N3906 PNP TO 92
R5410.0, 1/4 W, 1% North-South
R5510.0 K, 1/4 W, 1% North-South
R5610.0 K, 1/4 W, 1% West-East
R57499, 1/4W, 1% South-North
R581.00 K, 1/4 W, 1% West-East
R5922.1 K, 1/4W, 1% (omit for 40/80) West-East
R60499, 1/4W, 1% West-East
X0128.06 MHz and / or 28.224 MHz n/a
X0240.5 MHz n/a

Build Notes

LO Topside

LO - Bottomside


Mount a small wire loop to bridge the x4 holes, holes 1 and 2, of JP1. (This will result in each crystal frequency being divided by four in the clocking of the QSD and QSE circuits. The center frequency resulting from the x4 jumper will be approximately the crystal frequency divided by four) .

JP1 Loop


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 11.5 mA.
  • Set the ammeter back to voltage

Oscillator Output Waveform

  • Connect your scope lead to the left-hand loop on JP1 and the ground clip to the right hand loop.
  • Use the jumper and JP2 to select one or the other of the crystals.
  • Power up and observe the trace on the scope.
  • Depending upon the crystal selected, you should see a sinusoidal wave approximately 4.5 V p-p and frequency of 40.5, 28.224, or 28.060 MHz
LO Output for 28.224 MHz Xtal
(note: the scope used is quite limited, especially above 20 MHz. Frequency and voltage measurements are, at best, approximations).