TX Opamps Introduction


This stage has a pretty large part count.. It consists of four unitary gain op-amps, arranged in pairs, one per stereo line out signal into the board. The left channel's input resolves to two signals: 0 and 180. The right channel's input resolves to two signals: 90 and 270.

These four outputs will be muxed together in the Mixer Stage to produce the desired exciter output (thus, the term Quadrature Sampling Exciter (QSE)).

Theory of Operation

(see the Theory of Operation in the TX Mixer (QSE) Stage)

(go directly to build notes)

TX Opamps 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)
TX Opampsschematic

(above schematic has clickable areas that can be used for navigation)

(go directly to build notes)

TX Opamps Bill of Materials

Stage Bill of Materials

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

810 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4W
22.21 k 1/4W 1%r-r-br-br-br r-r-br-br-br1/4W
449.9 ohm 1%yel-wht-wht-gld-brn yel-wht-wht-gld-brn1/4W
1100k 1/6W 5%brn_blk_yel_gld brn_blk_yel_gld1/6W
40.022 uF 5%223 223Ceramic
2100 pF 5%101 101Ceramic
21000 pF 5%102 102Ceramic
14.7 uF 10% 16V X7R RAD475 475Ceramic
2shunt wire (cut-off lead)Cutoff
610uF/16 VDC Electrolytic
13.5mm stereo jack - PCB mount (rt-angle) Jack-RA
40.1 uF(smt) black stripe (smt) black stripeSMT 1206
2TLV2462CD dual opampTVL2462CD TVL2462CDSOIC-8

TX Opamps Summary Build Notes

TX Opamps Detailed Build Notes

Top of the Board

TX Opamps Top View

Install Topside Components

After installing R21 and R22, you might ant to run a quick powered test at the junction (R21 hairoin lead). R21/22 form a voltage divider on the 5 volt rail and you should see one-half the 5 volt rail voltage WRT regular ground (about 2.5 Vdc).

R212.21 k 1/4W 1%r-r-br-br-br r-r-br-br-br1/4WN-S
R222.21 k 1/4W 1%r-r-br-br-br r-r-br-br-br1/4WS-N
R2549.9 ohm 1%yel-wht-wht-gld-brn yel-wht-wht-gld-brn1/4WS-N
R2649.9 ohm 1%yel-wht-wht-gld-brn yel-wht-wht-gld-brn1/4WS-N
R2749.9 ohm 1%yel-wht-wht-gld-brn yel-wht-wht-gld-brn1/4WS-N
R2849.9 ohm 1%yel-wht-wht-gld-brn yel-wht-wht-gld-brn1/4WS-N
R1510 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4WS-N
R1610 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4WN-S
R1710 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4WW-E
R1810 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4WS-N
R1910 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4WN-S
R2010 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4WW-E
R2310 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4WE-W
R2410 k 1/4W 1%br-blk-blk-r-br br-blk-blk-r-br1/4WE-W
C08100 pF 5%101 101Ceramic 
C09100 pF 5%101 101Ceramic 
C041000 pF 5%102 102Ceramic 
C051000 pF 5%102 102Ceramic 
C150.022 uF 5%223 223Ceramic 
C160.022 uF 5%223 223Ceramic 
C170.022 uF 5%223 223Ceramic 
C180.022 uF 5%223 223Ceramic 
C104.7 uF 10% 16V X7R RAD475 475Ceramic 
C0610uF/16 VDC Electrolytic 
C0710uF/16 VDC Electrolytic 
C1110uF/16 VDC Electrolytic 
C1210uF/16 VDC Electrolytic 
C1310uF/16 VDC Electrolytic 
C1410uF/16 VDC Electrolytic 
R-TEST100k 1/6W 5%brn_blk_yel_gld brn_blk_yel_gld1/6W(Not supplied with kit)
Only needed for TX OpAmps functional test

Install IQ-In Jack and Jumpers

In both the RX op amp and TX QSE sections, the jumper links on the I/Q input and outputs should ideally be fitted crossed over. That provides compatibility with all versions of PowerSDR. For Rocky and Winrad it is necessary to use the 'swap IQ' functions in their set up. If you jumper them straight across fine for Rocky and Winrad, but you will not be able to use any version of PSDR. (Author wired for Rocky)

Recently, there have been extensive discussions on the reflector concerning the fact that some builders have a combination of soundcard, software, PC, and operating system in which the jumpers/leads for the TX I and Q signals must be the reverse of the jumpers/leads for the RX I and Q. This has been pretty much a case-by-case experience. We are building a spreadsheet depicting various combinations of the relevant variables (soundcard, program, kit, PS, OS, etc.) and the wiring that "works" for the RX and TX I and Q signals.

JP1Ashunt wire (cut-off lead)Cutoff 
JP1Bshunt wire (cut-off lead)Cutoff 
J33.5mm stereo jack - PCB mount (rt-angle) Jack-RA 

Bottom of the Board

TX Opamps Bottom View

Install Bottomside Components

U06TLV2462CD dual opampTVL2462CD TVL2462CDSOIC-8 
U07TLV2462CD dual opampTVL2462CD TVL2462CDSOIC-8 
C580.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C590.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C600.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C610.1 uF(smt) black stripe (smt) black stripeSMT 1206 

TX Opamps Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

TX Opamps Testing

Current Draw

Test Setup

Measure the current drawn by the 12V power supply with the 12V power connected. (if you have both the 12 V and trhe USB connected, the current drawr will be a little less than it would be without the USB connected.

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Current drawmA< 3526.6_______

OpAmps Functional Test

Test Setup

This test is similar to the test performed on the RX OpAmps.

You will need a 100k ohm resistor (not supplied with the kit) to perform the test. It involves connecting the 100k ohm resistor between pin 2 and ground for each Tx Opamp chip and measuring the output voltages at pins 1 and 7.

  • First, you measure the normal output voltages at pins 1 and 7
  • Then you connect the 100k ohm resistor between pin 2 (R15 hairpin) and ground
  • Then you remeasure the voltages at pins 1 and 7
  • And repeat the process for the second OpAmp, with its pin 2 (R18 hairpin) unbridged and bridged to ground
OpAmps Functional Test

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
U6-pin1 (R17 hairpin) - not bridgedV dc2.52.48_______
U6-pin7 - not bridgedV dc2.52.48_______
U6-pin1 (R17 hairpin) - R15 hairpin bridged 100k to groundV dc2.752.72_______
U6-pin7 - R15 hairpin bridged 100k to groundV dc2.252.23_______
U7-pin1 (R20 hairpin) - not bridgedV dc2.52.48_______
U7-pin7 not bridgedV dc2.52.48_______
U7-pin1 (R20 hairpin) - R18 hairpin bridged 100k to groundV dc2.752.72_______
U7-pin7 - R18 hairpin bridged 100k to groundV dc2.252.23_______

Pin Voltages

Test Setup

Power up the board and then measure the voltages at each of the pins of the two OpAmp Ics.

You should see the 5V rail voltage at pins 8, 0 Vdc at pins 4, and one half the 5 Volt rail at all other pins

If you do not get these voltages, carefullytake and compare the measurements on both the pin itself AND the pin PAD. If you get a different voltage on the pin vs. the pad, re-checl your soldering.

Pin Voltages

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Left IC, Pin 1Vdc2.52.48_______
Left IC, Pin 2Vdc2.52.48_______
Left IC, Pin 3Vdc2.52.48_______
Left IC, Pin 4Vdc00_______
Left IC, Pin 5Vdc2.52.48_______
Left IC, Pin 6Vdc2.52.48_______
Left IC, Pin 7Vdc2.52.48_______
Left IC, Pin 8Vdc54.96_______
Right IC, Pin 1Vdc2.52.48_______
Right IC, Pin 2Vdc2.52.48_______
Right IC, Pin 3Vdc2.52.48_______
Right IC, Pin 4Vdc00_______
Right IC, Pin 5Vdc2.52.48_______
Right IC, Pin 6Vdc2.52.48_______
Right IC, Pin 7Vdc2.52.48_______
Right IC, Pin 8Vdc54.96_______

OpAmp Outputs

Test Setup

If you have (access to) a dual channel scope, you may want to download Michael Keller, DL6iAK's IQ Gen and generate a dual tone quadrature signal for feeding into the "Line Out" Jack.

You can then probe the output resistors (R25-R28) to see the two anti-phase signals produced by this stage.

OpAmp Outputs
Go to External Connections Stage Go to Power Supply Stage Go to TX Mixers (QSE) Stage