Dividers Introduction
General
This phase installs the flip flop dividers, which divide the local oscillator's 28.188 MHz output into four quadrature signals, each at a frequency of 7.470 MHz and each 90 degrees out of phase with the other (0, 90, 180, 270).
The four divider outputs are color-coded on the schematic below, a color-coding scheme that will be used, as well, in the follow-on Mixer Phase.
These signals will be used to clock the quad bilateral switches in the mixer stage, which is closely patterned after the Tayloe detector (see discussion at page 18 of "A Software Defined Radio for the Masses, Part I"
Dividers Schematic
Dividers 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 | Orientation | Notes | Circuit |
|---|---|---|---|---|---|---|---|
| ❏ | 2 | 10 k 1/4W 1% | br-blk-blk-r-br
 | 1/4W | Dividers | ||
| ❏ | 4 | 100 1/4W 1% | br-blk-blk-blk-br
 | 1/4W | Dividers | ||
| ❏ | 1 | 10 nF (.01uF) | 103
 | Ceramic | Dividers | ||
| ❏ | 2 | 100 nF | 104
 | ceramic | Dividers | ||
| ❏ | 1 | 74AC(HC)74 Dual-D FF | 74HC74 or 74AC74
 | DIP-14 | Dividers |
Dividers Summary Build Notes
- Install All Divider Components
- Test the Stage
Dividers Detailed Build Notes
Top of the Board
Install All Divider Components
Be sure to orient the IC correctly (notch to the left). Also, make sure you have installed the 100 nF capacitor (above the IC), which couples the local oscillator signal into the divider stage.
| Check | Designation | Component | Marking | Category | Orientation | Notes |
|---|---|---|---|---|---|---|
| ❏ | E228 | 10 nF (.01uF) | 103
| Ceramic | ||
| ❏ | E44 | 100 nF | 104
| ceramic | ||
| ❏ | E83 | 100 nF | 104
| ceramic | ||
| ❏ | E89 | 74AC(HC)74 Dual-D FF | 74HC74 or 74AC74
| DIP-14 | Take ESD precautions | |
| ❏ | E126 | 100 1/4W 1% | br-blk-blk-blk-br
| 1/4W | ||
| ❏ | E139 | 100 1/4W 1% | br-blk-blk-blk-br
| 1/4W | ||
| ❏ | E94 | 100 1/4W 1% | br-blk-blk-blk-br
| 1/4W | ||
| ❏ | R12 | 100 1/4W 1% | br-blk-blk-blk-br
| 1/4W | ||
| ❏ | R96 | 10 k 1/4W 1% | br-blk-blk-r-br
| 1/4W | ||
| ❏ | R97 | 10 k 1/4W 1% | br-blk-blk-r-br
| 1/4W |
Dividers Testing
IC Voltages
Test Setup
Power ON and measure voltages (with respect to ground) at pins of the 74AC(HC)74 Dual-D FF IC
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| Pins 1, 4, 10, 13, and 14 | Vdc | +5 (Vdd) | +5.02 | _______ |
| pin 7 | Vdc | 0 | 0 | _______ |
| Pins 2, 5, 6, 8, 9, and 12 | Vdc | +2.5 | +2.49 | _______ |
| Pins 3 and 11 | Vdc | +2.5 | +2.52 | _______ |
Frequency Test
Test Setup
You can use an HF receiver tuned to 7.047 MHz to see if you detect the signals from the Dividers.
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| Nearby receiver tuned to 7.047 MHz receives signal | Y/N | Yes | Yes | _______ |
Frequency Test With Scope/Counter
Test Setup
If you have a scope or frequency counter, you can test the operation of the divider sub-phase:
- Powering up the board at 12 Vdc
- Probe each of the four pins: 5, 6, 8, and 9 on the 74AC74 chip.
- Each pin should register a frequency near 28.188/4=7.047 MHz.
- The wave forms should resemble those shown on the Mixer Schematic
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| pin 5 | MHZ | 7.047 (square) | 7.047 (square) | _______ |
| pin 6 | MHZ | 7.047 (square) | 7.047 (square) | _______ |
| pin 8 | MHZ | 7.047 (square) | 7.047 (square) | _______ |
| pin 9 | MHZ | 7.047 (square) | 7.047 (square) | _______ |