The Kit consists of two boards: Audio Switch (Fig.1) and ANT Switch (Fig.2). The Audio Switch board is controlled by the TRX PTT signal coming from the TRX. Consequently, the Audio Switch controls the audio paths and the ANT Switch.
Audio Switch board
- DC Power supply connector – from 10 to 15 volts. Without external relays the maximal current consumption is 55 mA in receive mode.
- TRX PTT – Input for transmit mode signal TRX PTT coming from TRX. It must be ground (0V) in transmit mode.
- Ant. Relay – Output driving the ANT Switch board.
- TRX/SDR Switch – External SPST switch which connects headphone audio permanently to TRX audio.
- TRX Audio – Input connected to TRX audio output.
- SDR audio – Input connected to SDR audio output (output of PC soundcard).
- Audio switch delay potentiometer – Setting the time delay of SDR audio signal. Turn clockwise to reduce the time delay.
- PTT LED – Red LED which is lit during receive mode.
- PTT LED connector – for external optional LED. Red dot is cathode. There is internal 10 K limiting resistor.
- AF LED – Green LED, lit when SDR audio is connected to headphones.
- AF LED connector – for external optional LED. Red dot is cathode. There is internal 10 K limiting resistor.
- Ant. relay 2 – Optional connector for 12 V external relays. Maximal source current is 200 mA. Synchronized with TRX PTT signal and is activated when TRX is in receive mode. Pins 1, 3 are ground and pin 2 is active (red dot marks the +). Reverse protection diode is not needed.
ANT Switch Board
- ANT – Connected to antenna.
- TRX – Connected to TRX antenna terminal.
- RX – Connected to SDR antenna terminal.
- CTRL – Connected to ANT Relay terminal of Audio Switch board.
- RX LED – Red LED is lit in receive mode (SDR is connected to ANT).
6. Jumper JP2 – Default position is pins 2 -3 shorted. Pin 1 is marked with an arrow.
7. Fuses R1, R5
8. Jumper JP1 – Must be shorted if the spare fuse R5 must be used.
Make sure that the Power Source (PS) for the Audio Switch is the same as for the TRX (e.g. TRX 12 V power supply). If this is not the case, the Audio Switch power supply and the TRX power supply should have a common ground. This is required by the “disconnected TRX PTT cable” protection circuit of the Kit. If there is no common ground, the Kit will always stay in transmit mode.
TRX PTT connection
First and foremost, check the output TRX PTT level of your transceiver. It must be 0 V (grounded) in transmit mode. This signal is used as control signal for power amplifier transmit/receive control or for other station automation. Icom uses the term “SEND” and usually is a separate RCA female connector at the rear panel. Yaesu is using the term “TX GND OUT” and for Kenwood it is named “MKE” (7 pin DIN connectors are used). Check the manuals and use the terminal which is intended to control the power amplifier state. In most modern transceivers this signal usually precedes the RF output signal with at least 10 ms, thus giving time for external relay circuits to settle.
Connect the transceiver TRX PTT output to the Audio Switch (black “PTT” line on Fig.4). This is the most important connection. If the board is not connected to the TRX PTT output, the TRX-SDR Switch will remain inactive in transmit mode (i.e. the SDR will be disconnected from the antenna).
Next, connect the “Control” line from the Audio Switch to the ANT Switch (in pink color on Fig.4).
Important: If you are going to use a Power Amplifier or other equipment which is also using the TRX PTT signal, please read here how to wire your setup.