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)).

Schematic

TX OpAmps Schematic

Bill of Materials

Designation Value Orientation
C02 0.001uF, ceramic, 10% n/a
C03 10uF/16 VDC Electrolytic East-West
C04 100pF, ceramic, 5% n/a
C05 10uF/16 VDC Electrolytic West-East
C06 0.022uF, ceramic, 5% n/a
C07 10uF/16 VDC Electrolytic North-South
C08 0.022uF, ceramic, 5% n/a
C09 0.001uF, ceramic, 10% n/a
C10 10uF/16 VDC Electrolytic East-West
C11 100pF, ceramic, 5% n/a
C12 10uF/16 VDC Electrolytic West-East
C13 0.022uF, ceramic, 5% n/a
C14 10uF/16 VDC Electrolytic West-East
C15 0.022uF, ceramic, 5% n/a
C16 10uF/16 VDC Electrolytic South-North
R03 10.0 K, 1/4 W, 1% East-West
R04 10.0 K, 1/4 W, 1% East-West
R05 49.9, 1/4W, 1% East-West
R06 10.0 K, 1/4 W, 1% East-West
R07 10.0 K, 1/4 W, 1% South-North
R08 49.9, 1/4W, 1% East-West
R09 10.0 K, 1/4 W, 1% South-North
R10 10.0 K, 1/4 W, 1% East-West
R11 49.9, 1/4W, 1% East-West
R12 10.0 K, 1/4 W, 1% East-West
R13 10.0 K, 1/4 W, 1% South-North
R14 49.9, 1/4W, 1% North-South
R15 2.21 K, 1/4W, 1% North-South
R16 2.21 K, 1/4W, 1% South-North
C51 0.1uF, smt 1206 smt
C52 0.1uF, smt 1206 smt
U01 TLV2462CD op-amp, SOIC 8 SOIC 8
U02 TLV2462CD op-amp, SOIC 8 SOIC 8

Build Notes

  • Need to do topside components first, as many holes for these are very close to the IC pads on the bottomside - avoiding solder splashover

Install the 8 Ceramic Capacitors

TX OpAmp Ceramic Caps

Install C2, C4, C6, C8, C9, C11, C13, and C15
Designation Value Orientation
C02 0.001uF, ceramic, 10% n/a
C04 100pF, ceramic, 5% n/a
C06 0.022uF, ceramic, 5% n/a
C08 0.022uF, ceramic, 5% n/a
C09 0.001uF, ceramic, 10% n/a
C11 100pF, ceramic, 5% n/a
C13 0.022uF, ceramic, 5% n/a
C15 0.022uF, ceramic, 5% n/a

Install the 7 Electrolytic Capacitors

TX OpAmp Electrolytic Caps

Install C3, C5, C7, C10, C12, C14, and C16
Designation Value Orientation
C03 10uF/16 VDC Electrolytic East-West
C05 10uF/16 VDC Electrolytic West-East
C07 10uF/16 VDC Electrolytic North-South
C10 10uF/16 VDC Electrolytic East-West
C12 10uF/16 VDC Electrolytic West-East
C14 10uF/16 VDC Electrolytic West-East
C16 10uF/16 VDC Electrolytic South-North

Install the 14 Resistors

TX OpAmp Resistors

Install Resistors R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13, R14, R15, R16
Designation Value Orientation
R03 10.0 K, 1/4 W, 1% East-West
R04 10.0 K, 1/4 W, 1% East-West
R05 49.9, 1/4W, 1% East-West
R06 10.0 K, 1/4 W, 1% East-West
R07 10.0 K, 1/4 W, 1% South-North
R08 49.9, 1/4W, 1% East-West
R09 10.0 K, 1/4 W, 1% South-North
R10 10.0 K, 1/4 W, 1% East-West
R11 49.9, 1/4W, 1% East-West
R12 10.0 K, 1/4 W, 1% East-West
R13 10.0 K, 1/4 W, 1% South-North
R14 49.9, 1/4W, 1% North-South
R15 2.21 K, 1/4W, 1% North-South
R16 2.21 K, 1/4W, 1% South-North

Install the Op-Amps and SMT caps

TX OpAmp Bottomside

Install U1, U2, C51, and C52

Watch out for solder splashover on any adjacent, open holes

Designation Value Orientation
C51 0.1uF, smt 1206 smt
C52 0.1uF, smt 1206 smt
U01 TLV2462CD op-amp, SOIC 8 SOIC 8
U02 TLV2462CD op-amp, SOIC 8 SOIC 8

Testing

Current Draw

  • With limiting resistor:
  • Without Limiting resistor (should be 34-36 mA  ):

Op-Amp Voltage Divider (R15/R16)

  • R15/R16 form a voltage divider to halve the 5 Vdc rail
  • measure the voltage wrt ground at the R16 hairpin.
  • You should see 2.5 Vdc

Op-Amp Pin Voltages

  • Measure the voltages at the pins of U1 and U2 using the table below
  • You should measure at the actual pins on the ICs as well as using the convenient resistor hairpin testpoints
U1
PinExpected ValueAuthor ResultAs Measured
1 (R6 hairpin)2.5 Vdc
2 (R4 hairpin)2.5 Vdc
3 (R16 hairpin)2.5 Vdc
40 (gnd)
5 (R16 hairpin)2.5 Vdc
6 (R7 hairpin)2.5 Vdc
7 2.5 Vdc
8 (R15 hairpin)+5 Vdc
U2
PinExpected ValueAuthor ResultAs Measured
1 (R12 hairpin)2.5 Vdc
2 (R10 hairpin)2.5 Vdc
3 (R16 hairpin)2.5 Vdc
4 0 (gnd)
5 (R16 hairpin)2.5 Vdc
6 (R13 hairpin)2.5 Vdc
7 2.5 Vdc
8 (R15 hairpin)+5 Vdc

Op-Amp Function

  • set up Rocky or IQGen to transmit using a center frequency of 7.056 MHz and transmitting on 7.040 MHz at approximately 215 mV p-p
  • connect the board to the PC via a stereo cable to the Line out L and Line Out R (and common) connectors
  • clip the scope probes to R5's hairpin (the 0° output of U1) and R8's hairpin (the 180° output of U1)
  • You should see equal signals 180° out of phase with one another and at a frequency of approximately 16 kHz
  • Repeat the process for U2, using R11 and R14, in lieu of R5 and R8, for the 90° and 270° outputs, respectively
Left Channel OpAmp Output