Mixers Introduction
General
The G40's mixer is a double-balanced, sample and hold circuit using two quad bilateral analog switches (74HC4066), clocked by the four outputs from the dividers.
Each pair of switches outputs to an RC pair that samples and holds the output for forwarding to the OpAmps Section. The portion of the schematic illustrating this is shown below (including divider output waveforms derived from a simulation of the divider operation). Not shown is that part of the circuit that uses two 5k trimpots for hardware balancing of the mixer.
The incoming RF is split into 2 streams, each going to two pairs of switches. Each switch pair is turned on and off by a signal coming from the dividers. The switched outputs of the pair are integrated by the corresponding RC circuit. As in theTayloe detector, the result is the down-conversion of the RF signals to their AF analogues.
The resultant outputs of the mixers' RC circuits will go to the OpAmp chains to produce the I and Q audio signals for the PC.
Mixers Schematic
Mixers 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 | 220 1/4W 1% | red-red-blk-blk-brn
 | 1/4W | Mixers | ||
| ❏ | 4 | 33 1/4W 1% | ora-ora-blk-gld-brn
 | 1/4W | Mixers | ||
| ❏ | 2 | 100 nF | 104
 | ceramic | Mixers | ||
| ❏ | 1 | 22 nF USM | 223J
 | Ceramic | Shown as "C10" on graphic | Mixers | |
| ❏ | 1 | 22 nF USM | 223J
| Ceramic | Shown as "C11" on graphic | Mixers | |
| ❏ | 1 | 22 nF USM | 223J
| Ceramic | Shown as "C12" on graphic | Mixers | |
| ❏ | 1 | 22 nF USM | 223J
| Ceramic | Shown as "C9" on graphic | Mixers | |
| ❏ | 3 | 47 uH molded inductor | yel-vio-blk-gld
 | choke | Mixers | ||
| ❏ | 2 | 74HC4066 Quad Bilateral SW |
 | DIP-14 | Mixers | ||
| ❏ | 1 | 220 uF/16Vdc |
 | Electrolytic | Mixers |
Mixers Summary Build Notes
- Install All Mixer Components
- Test the Stage
Mixers Detailed Build Notes
Top of the Board
Install All Mixer Components
Be careful installing the two 220 Ohm resistors. Avoid letting the two prozimate leads touch each other or solder splash. This will become evident in the testing below.
| Check | Designation | Component | Marking | Category | Orientation | Notes |
|---|---|---|---|---|---|---|
| ❏ | E20 | 100 nF | 104
| ceramic | ||
| ❏ | E23 | 100 nF | 104
| ceramic | ||
| ❏ | E149 | 220 uF/16Vdc |
| Electrolytic | ||
| ❏ | C12 | 22 nF USM | 223J
| Ceramic | Shown as "C12" on graphic | |
| ❏ | C11 | 22 nF USM | 223J
| Ceramic | Shown as "C11" on graphic | |
| ❏ | C10 | 22 nF USM | 223J
| Ceramic | Shown as "C10" on graphic | |
| ❏ | C9 | 22 nF USM | 223J
| Ceramic | Shown as "C9" on graphic | |
| ❏ | E140 | 74HC4066 Quad Bilateral SW |
| DIP-14 | Take ESD precautions | |
| ❏ | E92 | 74HC4066 Quad Bilateral SW |
| DIP-14 | Take ESD precautions | |
| ❏ | E75 | 47 uH molded inductor | yel-vio-blk-gld
| choke | ||
| ❏ | E95 | 47 uH molded inductor | yel-vio-blk-gld
| choke | ||
| ❏ | L1 | 47 uH molded inductor | yel-vio-blk-gld
| choke | ||
| ❏ | E2 | 220 1/4W 1% | red-red-blk-blk-brn
| 1/4W | ||
| ❏ | E99 | 220 1/4W 1% | red-red-blk-blk-brn
| 1/4W | ||
| ❏ | E102 | 33 1/4W 1% | ora-ora-blk-gld-brn
| 1/4W | ||
| ❏ | E102 | 33 1/4W 1% | ora-ora-blk-gld-brn
| 1/4W | ||
| ❏ | E73 | 33 1/4W 1% | ora-ora-blk-gld-brn
| 1/4W | ||
| ❏ | E96 | 33 1/4W 1% | ora-ora-blk-gld-brn
| 1/4W |
Mixers Testing
Visual Inspection
Test Setup
Carefully inspect all solder joints for bridges and.or cold solder joints
Voltage Tests
Test Setup
Test the +5 and _2.5 volt rails at the testpoints indicated below:
Test Measurements
| Testpoint | Units | Nominal Value | Author's | Yours |
|---|---|---|---|---|
| right-hand lead of 220 ohm resistor (marked "+5") | V dc | 5 | 5.02 | _______ |
| left-hand lead of 220 ohm resistor (marked "+2.5") | V dc | 2.5 | 2.43 | _______ |