Quadrature Clock Generator Introduction
General
This stage divides the local oscillator output by 4 and shifts the phase of the dividend signals such that they are now one-fourth the LO frequency and 90 degrees separated in phase (i.e., in quadrature). Both signals are identical in all regards except phase. They will be used to clock the switch used in the Quadrature Sampling Detector (QSD) stage.
(go directly to build notes)Quadrature Clock Generator Schematic
(Resistor testpoints (hairpin, top, or left-hand lead), as physically installed on the board, are marked in the schematic with red dots)
(Click for Full Schematic)
(above schematic has clickable areas that can be used for navigation)
(go directly to build notes)Quadrature Clock Generator Bill of Materials
Stage Bill of Materials
(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)
| Check | Count | Component | Marking | Category |
|---|---|---|---|---|
| ❏ | 2 | 10 k 1/6W 5% | brn-blk-ora-gld
 | 1/6W |
| ❏ | 1 | 0.1 uF | (smt) black stripe
 | SMT 1206 |
| ❏ | 1 | 74AC74 Dual D FF | 74AC74
 | SOIC-14 |
Quadrature Clock Generator Summary Build Notes
- Install Voltage Divider Resistors
- Install IC and SMT Capacitor
- Test the Stage
Quadrature Clock Generator Detailed Build Notes
Bottom of the Board
Install IC and SMT Capacitor
| Check | Designation | Component | Marking | Category | Orientation | Notes |
|---|---|---|---|---|---|---|
| ❏ | U06 | 74AC74 Dual D FF | 74AC74
| SOIC-14 |  | Take ESD precautions Markings vary - look for "AC74" |
| ❏ | C36 | 0.1 uF | (smt) black stripe
| SMT 1206 | yellow pads |
Top of the Board
Install Voltage Divider Resistors
Pay careful attention to the orientation (S-N and N-S, respectively) of R10 and R11. Some builders have inadvertently installed these with a horizontal orientation rather than a vertical orientation.
| Check | Designation | Component | Marking | Category | Orientation | Notes |
|---|---|---|---|---|---|---|
| ❏ | R10 | 10 k 1/6W 5% | brn-blk-ora-gld
| 1/6W | S-N | |
| ❏ | R11 | 10 k 1/6W 5% | brn-blk-ora-gld
| 1/6W | N-S |
Quadrature Clock Generator Completed Stage
Top of the Board
Bottom of the Board
Quadrature Clock Generator Testing
Current Draw
Test Setup
With both the USB cable and the power cable plugged in, measure the current draw in the positive power lead.
Measure the current draw with just the 12V power.
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| Current draw WITH USB | mA | < 18 | 9.8 | _______ |
| Current draw NO USB | mA | < 20 | 13.7 | _______ |
Test Voltage Divider
Test Setup
When performing the following tests, you must apply [pwer to the board AND plug in the USB cable. Otherwise, results will not be as expected.
Plug in USB and power the board.
Measure the voltage on the R11 hairpin; you should see 50% of the %v rail voltage.
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| R11 hairpin (WRT regular gnd) | V dc | 2.5 | 2.46 | _______ |
Divider Pin Voltages
Test Setup
Power USB and 12V. Then measure the voltages on the pins (and, separately, on the pads) of U6 (74AC74). Refer to the color codes on the graphic for the voltages.
Pins 3 and 11 will not show exactly 2.5Vdc because they have the additional AC component of the local oscillator signal from C3.
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| Pin 1 | Vdc | 5 | 4.92 | _______ |
| Pin 2 | Vdc | 2.5 | 2.45 | _______ |
| Pin 3 | Vdc | 2 to 3 | 2.46 | _______ |
| Pin 4 | Vdc | 5 | 4.92 | _______ |
| Pin 5 | Vdc | 2.5 | 2.45 | _______ |
| Pin 6 | Vdc | 2.5 | 2.45 | _______ |
| Pin 7 | Vdc | 0 (GND) | 0 | _______ |
| Pin 8 | Vdc | 2.5 | 2.45 | _______ |
| Pin 9 | Vdc | 2.5 | 2.45 | _______ |
| Pin 10 | Vdc | 5 | 4.92 | _______ |
| Pin 11 | Vdc | 2.5 | 2.46 | _______ |
| Pin 12 | Vdc | 2 - 3 | 2.45 | _______ |
| Pin 13 | Vdc | 5 | 4.92 | _______ |
| Pin 14 | Vdc | 5 | 4.92 | _______ |
Quadrature Colck Generated Waveforms
Test Setup
Set your board up to oscillate at a selected center frequency, e.g., 7.100 MHz.
If you have a dual trace scope available, probe the two "QSD CLK (n)" test points and you should get a waveform similar to the one shown here.
Your mileage may vary, depending upon the desired center frequency you select and the quality of your scope (some scopes tend to have issues with these square waves - still, the scope should show two waveforms in quadrature at the desired center frequency).
