Introduction

This stage handles the muting of the RX section when I PTT goes high. When RX Mute is High, the RX Mixer is disabled; when RX Mute goes low (the normal power up value), the RX Mixer is enabled.

Schematic

RXTX Switching Circuit

Bill of Materials

Designation Value Orientation
Q11 2N3904 NPN TO 92
Q12 2N3904 NPN TO 92
R39 4.99 K, 1/4W, 1% West-East
R40 22.1 K, 1/4W, 1% East-West
R41 10.0 K, 1/4 W, 1% South-North
R42 221, 1/4 W, 1% North-South
R43 22.1 K, 1/4W, 1% East-West

Build Notes

RX Switching

Testing

Current Draw

  • current draw should be at ~38 mA

RX Muting

  • set I PTT to high by connecting R33 hairpin to R35 hairpin with a clip lead
  • Measure the RX Mute signal (at R45 hairpin). You should get a high signal (~5 Vdc)
  • Measure the voltage at the S12V pad. You should get 10-12 Vdc
  • set I PTT to low by disconnecting the lead between R33 and R35
  • Measure the RX Mute signal (at R45 hairpin). You should get a low signal (~50 mVdc)
  • Measure the voltage at the S12V pad. You should get ~0 Vdc