This stage adds the TX Mixer to the board and provides the modulation of the Dividers' output signals by the 4 I and Q signals from the OpAmps. The result is a double sideband RF waveform that will be coupled into the PA stage.


TX Mixer Schematic

Bill of Materials

Designation Value Orientation
C17 10uF/16 VDC Electrolytic South-North
C18 150pF, ceramic, 5% n/a
C53 0.1uF, smt 1206 smt
R17 3.32 K, 1/4W, 1% East-West
R18 2.21 K, 1/4W, 1% West-East
R19 49.9, 1/4W, 1% North-South
R20 49.9, 1/4W, 1% West-East
T01 T30-6 (yellow) (#30) (2.1 uH) 24T/2x11T
U03 FST3253 or SN74CBT3253D SOIC 16

Build Notes

TX Mixer Topside

TX Mixer Bottomside


Current Draw

  • With limiting resistor:
  • Without limiting resistor, you should get ~38.5 mA

Mixer Output

  • Enable the chip. Connect the R39 hairpin hole to ground. Take care to get the correct hole (the right-hand, hairpin hole)
  • Inject 16kHz audio signal into line in Left (or right). (Can use Rocky or IQGen to provide signals out of the computer's sound card)
  • Connect scope probe to the top right pad of L1
  • The trace should show a clean double sideband signal.
  • Try the same for the other line out feed.