Local Oscillator Introduction


The local oscillator stage generates a 28.188 MHz signal (for quadrature clocking signals of 7.047 MHz each) using a 74HC04 hex inverter and a 21.188 MHz crystal.

The circuit is described in the schematic "Oscillator Connection Genesis G** Design".

The output of this stage will divided in the follow-on stage.

Local Oscillator Schematic

Local Oscillatorschematic

Local Oscillator Bill of Materials

Stage Bill of Materials

(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)

2330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W  Local Oscillator
14K7 1/4W 1% (4.7K)yel-vio-blk-brn-brn yel-vio-blk-brn-brn1/4W  Local Oscillator
356 1/4W 1%grn-blu-blk-gld-brn1/4W  Local Oscillator
110 nF (.01uF)103 103Ceramic  Local Oscillator
1100 nF104 104ceramic  Local Oscillator
233 pF33JCeramic  Local Oscillator
174HC04 Hex Inverter DIP-14  Local Oscillator
1100 uF/25Vdc Electrolytic  Local Oscillator
1BNC Connector Male - PCB mountjack NOT SUPPLIED WIT KIT Local Oscillator
4shunt wire (cut-off lead)misc  Local Oscillator
128.188 MHzXtal Local Oscillator

Local Oscillator Summary Build Notes

Local Oscillator Detailed Build Notes

Top of the Board

Local Oscillator Top View

Install Jumpers

Install the four jumpers, using cut-off leads from the preceding phase. Be careful to observe the correct holes for the jumpers (see the graphic, above).

jmp1shunt wire (cut-off lead)misc 
jmp2shunt wire (cut-off lead)misc 
jmp3shunt wire (cut-off lead)misc 
jmp4shunt wire (cut-off lead)misc 

Install the IC

Install the IC before installing the remainder of the components, as it "nestles" among some components. Pay careful attention to the orientation of the IC (notch facing the top edge of the board).

Before inserting the IC, straighten the leads:

straightening pins on Ics

E35974HC04 Hex Inverter DIP-14 
Take ESD precautions

Install Remaining LO Conponents

Parts placment is fairly straight-forward and localized to the top left side of the board.

The only potential point of confusion is the 100k resistor which is NOT used (a 4.7k resistor is used, instead). The change was made too late to modify the pcb's silkscreen.

Additionally, please note that the BNC connector specified in the Bill of Materials is NOT supplied with the kit. It is used only if you are planning on incorporating an external oscillator in lieu of the internal oscillator.

It is a good idea to keep a small separation between the bottom of the crystal and the top of the board when installing the crystals. One way to do this is to insert a tiny piece of folded paper underneath the crystal to act as a separator "shim".

E9310 nF (.01uF)103 103Ceramic 
E351100 nF104 104ceramic 
E86100 uF/25Vdc Electrolytic 
E35333 pF33JCeramic 
E36733 pF33JCeramic 
E18656 1/4W 1%grn-blu-blk-gld-brn1/4W 
E35456 1/4W 1%grn-blu-blk-gld-brn1/4W 
E38456 1/4W 1%grn-blu-blk-gld-brn1/4W 
E364330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W 
E40330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W 
E3634K7 1/4W 1% (4.7K)yel-vio-blk-brn-brn yel-vio-blk-brn-brn1/4W 
E37128.188 MHzXtal 
E180BNC Connector Male - PCB mountjack 

Local Oscillator Testing

LO Voltage Testing

Test Setup

Refer to above PCB layout for the two voltage testpoints

  • Connect the power supply as in Phase 1.
  • Check the pin voltages shown in the table
  • If the voltages are close to 0 or +5V, then the oscillator is not working correctly.

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
pin 11 of the 74HC04V dc+1.5 - +3.9+2.59_______
pin 12 of the 74HC04V dc+1.5 - +3.9+2.43_______

Frequency Test

Test Setup

If you have a frequency counter or HF transceiver, look for a signal around 28.188 MHz to verify that the oscillator is providing output.

If you have an oscilloscope, you can probe at the "LO Out" testpoint (see above) for the 28.188 MHz signal.