Mixers Introduction


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)

2220 1/4W 1%red-red-blk-blk-brn red-red-blk-blk-brn1/4W  Mixers
433 1/4W 1%ora-ora-blk-gld-brn ora-ora-blk-gld-brn1/4W  Mixers
2100 nF104 104ceramic  Mixers
122 nF USM223J 223JCeramic  Shown as "C10" on graphicMixers
122 nF USM223J 223JCeramic  Shown as "C11" on graphicMixers
122 nF USM223J 223JCeramic  Shown as "C12" on graphicMixers
122 nF USM223J 223JCeramic Shown as "C9" on graphicMixers
347 uH molded inductoryel-vio-blk-gld yel-vio-blk-gldchoke  Mixers
274HC4066 Quad Bilateral SW DIP-14  Mixers
1220 uF/16Vdc Electrolytic  Mixers

Mixers Summary Build Notes

Mixers Detailed Build Notes

Top of the Board

Mixers Top View

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.

E20100 nF104 104ceramic 
E23100 nF104 104ceramic 
E149220 uF/16Vdc Electrolytic 
C1222 nF USM223J 223JCeramic 
Shown as "C12" on graphic
C1122 nF USM223J 223JCeramic 
Shown as "C11" on graphic
C1022 nF USM223J 223JCeramic 
Shown as "C10" on graphic
C922 nF USM223J 223JCeramic 
Shown as "C9" on graphic
E14074HC4066 Quad Bilateral SW DIP-14 
Take ESD precautions
E9274HC4066 Quad Bilateral SW DIP-14 
Take ESD precautions
E7547 uH molded inductoryel-vio-blk-gld yel-vio-blk-gldchoke 
E9547 uH molded inductoryel-vio-blk-gld yel-vio-blk-gldchoke 
L147 uH molded inductoryel-vio-blk-gld yel-vio-blk-gldchoke 
E2220 1/4W 1%red-red-blk-blk-brn red-red-blk-blk-brn1/4W 
E99220 1/4W 1%red-red-blk-blk-brn red-red-blk-blk-brn1/4W 
E10233 1/4W 1%ora-ora-blk-gld-brn ora-ora-blk-gld-brn1/4W 
E10233 1/4W 1%ora-ora-blk-gld-brn ora-ora-blk-gld-brn1/4W 
E7333 1/4W 1%ora-ora-blk-gld-brn ora-ora-blk-gld-brn1/4W 
E9633 1/4W 1%ora-ora-blk-gld-brn ora-ora-blk-gld-brn1/4W 

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:

Voltage Tests

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
right-hand lead of 220 ohm resistor (marked "+5")V dc55.02_______
left-hand lead of 220 ohm resistor (marked "+2.5")V dc2.52.43_______