Local Oscillators Introduction


This phase provides the local oscillator functionality, ultimately yielding four different center frequencies, one for the 30m band and three for the 20m band:

The Local Oscillator stage produces 4 crystal-controlled frequencies, each of which is 4 times the desired center frequency (those LO frequencies will be divided by 4 in a follow-on stage to get to the desired center frequencies.

The center frequencies provide a bandwith of either +- 24 kHZ or +- 48 kHz, depending upon the soundcard's sampling frequency of 48kHz or 96 kHz:

Crystal48kHz Bandwidth96kHz Bandwidth
(40.5 MHz) 30m: center = 10.125 MHz 10.101MHz - 10.149MHz10.077MHz - 10.173MHz
(56.180 MHz) 20m: center=14.045 MHz 14.021MHz - 14.069MHz13.997MHz - 14.093MHz
(56.552 MHz) 20m: center = 14.138 MHz 14.114MHz - 14.162MHz14.090MHz - 14.186MHz
(56.928 MHz) 20m: center = 14.232 MHz 14.208MHz - 14.256MHz14.184MHz - 14.280MHz

The local oscillator stage generates signals (for quadrature clocking signals of 1/4 of the selected output frequency) using a 74HC04 hex inverter and a freequency-specific crystals.

The circuit is described in more detail in the schematic "Oscillator Connection Genesis G** Design" (including the facility to bypass the internal oscillator and use, in its stead, an external oscillator).

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

(go directly to build notes)

Local Oscillators Schematic

Local Oscillatorsschematic

(go directly to build notes)

Local Oscillators Bill of Materials

Stage Bill of Materials

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

4100k 1/4W 1%brn-blk-blk-orng-brn brn-blk-blk-orng-brn1/4W
610K 1/4W 1%brn-blk-blk-red-brn brn-blk-blk-red-brn1/4W
5330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W
44K7 1/4W 1% (4.7K)yel-vio-blk-brn-brn yel-vio-blk-brn-brn1/4W
41N41481N4148 1N4148Axial
610 nF (.01uF)103 103Ceramic
6100 nF104 104Ceramic
4470 nH molded inductor (0.47 uH)yel-vio-slv_gld yel-vio-slv_gldChoke
274HC04 Hex Inverter DIP-14
412 pF disc ceramic12J 12JDisc
315 pF disc ceramic15J 15JDisc
122 pF disc ceramic22J 22JDisc
1100 uF/25Vdc Electrolytic
4BC546 NPN Transistor TO-92
140.500 MHz HC48S Crystal Xtal
156.180 MHz HC48S Crystal Xtal
156.552 MHz HC48S Crystal Xtal
156.928 MHz HC48S Crystal Xtal

Local Oscillators Summary Build Notes

Local Oscillators Detailed Build Notes

Top of the Board

Local Oscillators Top View

Install Diodes

Watch out on the diodes; one of them (D2-2) has its orientation (its band orientation) different from the other three

There are also 4 chokes (note they are all 470 nH (nano), NOT 47 uH (micro)). Check the color codes.

Note: The wires shown as black dotted lines on the graphic below illustrate the 4 possible, temporary connections (to the 5V present at the noted Jumper) needed to enable one of the 4 crystals. Ignore these until the testing section.

Install Diodes photo
D2-11N41481N4148 1N4148AxialBand on left
D2-21N41481N4148 1N4148AxialBand on right
D2-31N41481N4148 1N4148AxialBand on left
D2-41N41481N4148 1N4148AxialBand on left
L2-1470 nH molded inductor (0.47 uH)yel-vio-slv_gld yel-vio-slv_gldChoke 
L2-2470 nH molded inductor (0.47 uH)yel-vio-slv_gld yel-vio-slv_gldChoke 
L2-3470 nH molded inductor (0.47 uH)yel-vio-slv_gld yel-vio-slv_gldChoke 
L2-4470 nH molded inductor (0.47 uH)yel-vio-slv_gld yel-vio-slv_gldChoke 

Install the Passive Components

Watch out for those square pass-through holes

potential errorr

For example, in the above image, there are three different resistors where the builder can accidentally install the resistor into the round hole on one end and the square hole on the other; the holes should be round for the correct installation.

Install the Passive Components photo
C2-21100 uF/25Vdc Electrolytic"+" (longer lead) is on left
R2-1330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W 
R2-2330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W 
R2-3330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W 
R2-4330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W 
R2-5330 1/4W 1%ora-ora-blk-blk-brn ora-ora-blk-blk-brn1/4W 
R2-64K7 1/4W 1% (4.7K)yel-vio-blk-brn-brn yel-vio-blk-brn-brn1/4W 
R2-74K7 1/4W 1% (4.7K)yel-vio-blk-brn-brn yel-vio-blk-brn-brn1/4W 
R2-84K7 1/4W 1% (4.7K)yel-vio-blk-brn-brn yel-vio-blk-brn-brn1/4W 
R2-94K7 1/4W 1% (4.7K)yel-vio-blk-brn-brn yel-vio-blk-brn-brn1/4W 
R2-1010K 1/4W 1%brn-blk-blk-red-brn brn-blk-blk-red-brn1/4W 
R2-1110K 1/4W 1%brn-blk-blk-red-brn brn-blk-blk-red-brn1/4W 
R2-1210K 1/4W 1%brn-blk-blk-red-brn brn-blk-blk-red-brn1/4W 
R2-1310K 1/4W 1%brn-blk-blk-red-brn brn-blk-blk-red-brn1/4W 
R2-1410K 1/4W 1%brn-blk-blk-red-brn brn-blk-blk-red-brn1/4W 
R2-1510K 1/4W 1%brn-blk-blk-red-brn brn-blk-blk-red-brn1/4W 
R2-16100k 1/4W 1%brn-blk-blk-orng-brn brn-blk-blk-orng-brn1/4W 
R2-17100k 1/4W 1%brn-blk-blk-orng-brn brn-blk-blk-orng-brn1/4W 
R2-18100k 1/4W 1%brn-blk-blk-orng-brn brn-blk-blk-orng-brn1/4W 
R2-19100k 1/4W 1%brn-blk-blk-orng-brn brn-blk-blk-orng-brn1/4W 
C2-1312 pF disc ceramic12J 12JDisc 
C2-1412 pF disc ceramic12J 12JDisc 
C2-1512 pF disc ceramic12J 12JDisc 
C2-1612 pF disc ceramic12J 12JDisc 
C2-1715 pF disc ceramic15J 15JDisc 
C2-1815 pF disc ceramic15J 15JDisc 
C2-1915 pF disc ceramic15J 15JDisc 
C2-2022 pF disc ceramic22J 22JDisc 
If 30m Oscillator is not working, try upping this to 27pF (e.g., add a 5.6 or 6.8 pF in parallel)
C2-110 nF (.01uF)103 103Ceramic 
C2-210 nF (.01uF)103 103Ceramic 
C2-310 nF (.01uF)103 103Ceramic 
C2-410 nF (.01uF)103 103Ceramic 
C2-510 nF (.01uF)103 103Ceramic 
C2-610 nF (.01uF)103 103Ceramic 
C2-10100 nF104 104Ceramic 
C2-11100 nF104 104Ceramic 
C2-12100 nF104 104Ceramic 
C2-7100 nF104 104Ceramic 
C2-8100 nF104 104Ceramic 
C2-9100 nF104 104Ceramic 

Install Active Components

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".

When installing the 74HC04N ICs, pay close attention to their orientation. The end with the dimple corresponds to the silkscreen end with a notch in it. Pin 1 of the IC is as indicated in the graphic on the bill of materials.

Be careful not to confuse the BC546 (NPN) transistors with the nearly identical looking BC556 (PNP) transistors.

Note the orientation of the transistors on the board: they are mounted such that the flat side of the transistor is aligned with the flat dimension of the silkscreened layout for the transistor and, again, be sure to mount the correct transistor (BC546, not BC556):

mounting a transistor - orientationj Wrong component!

Install Active Components photo
U2-174HC04 Hex Inverter DIP-14 
Take ESD precautions
U2-274HC04 Hex Inverter DIP-14 
Take ESD precautions
Q2-1BC546 NPN Transistor TO-92 
Q2-2BC546 NPN Transistor TO-92 
Q2-3BC546 NPN Transistor TO-92 
Q2-4BC546 NPN Transistor TO-92 
X2-140.500 MHz HC48S Crystal Xtal 
X2-256.180 MHz HC48S Crystal Xtal 
X2-356.552 MHz HC48S Crystal Xtal 
X2-456.928 MHz HC48S Crystal Xtal 

Inspect Completed Board

Visually inspect the board, paying close attention to the following, which have caused problems for some builders:

  1. Inductors (all four must be 470 nH yellow-biolet-silver-gold)
  2. ICs (both must be 74HC04)
  3. Transistors (all four must be BC546, not BC556) and oriented with their flat sides toward the bottom edge of the board.
  4. Diodes: of the four 1N4148s, three are oriented with their bands on the LEFT and one has the band on the RIGHT)
  5. Crystals: separated slightly from the board and in the correct positions (per the layout diagram). Note that, just in the photo below, one crystal was not available for installatin at the time the photo was taken. You should have all four crystals installed.
  6. Capacitors: double check the band-specific capacitors for correct values and placement (i.e., the values in addition to the customary 103 and 104 capacitors)
  7. Resistors: recall from above that there are three "opportunities for mischief" in this stage, whereby the builder solders one lead of a resistor into a square hole instead of a round hole. Carefully check each of those locations and be sure you got it right.
  8. Inspect the underside for solder bridges, cold joints, etc.

Inspect Completed Board photo

Local Oscillators Testing

Oscillator Output Tests

Test Setup

The first oscillator to check is one for 30m band which resonates at 40500 kHz.

1. solder temporary wire (as "W1-a") between jumper JK1 and JP1 pin 3. (You may prefer to use a wire with test clips on either end as Wire1 (rather than soldering and unsoldering).

2. check the voltage at test point TP1 with digital multi meter. It should read around +2V. If the test voltage is 0V or 5V then oscillator is not oscillating.

3. in same way test three remaining oscillators by connecting W1 wire:

  • As "W1-b" to points JP1 pin 1 (56.180MHz)
  • As "W1-c" to JP2 pin 2 (56.552MHz) and
  • As "W1-d" to JP2 pin 1 (56.928MHz)

(In the dividers stage, we will check the oscillator's functionality again, but at frequencies sensible to the average HF RX)

Some builders have had difficulties getting the 30m Oscillator to work. If this is your case, check out message 1467 in the Yahoo Group, calling for replacing the 22pF capacitor with a 27pF capacitor.

Oscillator Output Tests

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
40.5MHz (10.125): W1=JK1-JP1-3 (TestPoint TP1)Vdc+23.382_______
56.18MHz (14.045): W1=JK1-JP1-1 (TestPoint TP1)Vdc+23.374_______
56.552MHz (14.138): W1=JK1-JP2-2 (TestPoint TP1)Vdc+23.382_______
56.928MHz (14.232): W1=JK1-JP2-1 (TestPoint TP1)Vdc+23.431_______
LO Out (junction of 2 10k resistors - voltage divider)Vdc+2.52.51_______

Frequency Output

Test Setup

If you have a frequency counter or scope, connect each of the four oscillators, in turn, and look for a signals to verify that the oscillator is providing output.

You can probe at the "LO Out" testpoint (see above) for the desired signal.

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
LO Out: 40.5 MHz selectedMHz40.540.5_______
LO Out: 56.18 MHz selectedMHz56.1856.18_______
LO Out: 56.552 MHz selectedMHz56.55256.55_______
LO Out: 56.928 MHz selectedMHz56.92856.93_______