Tests to Check the Functionality of the SDR/TRX Switch

Application notes

audio switch board annotated
Fig.1 – Audio Switch board
Fig.2 Test the TRX/PTT input of the Audio switch board

Do not connect the transceiver

Connect the Audio switch and Antenna switch. (Fig.2) with prepared cable

Connect the power supply and switch it on. All LEDs must be OFF, the board is not powered.

Connect the outer pin (the ring of the RCA connector) of 2 (TRX PTT [IN], J2) to the power supply ground (0V) with a test cable. This connector senses if there is a ground

Now the board is powered and all LEDs must be ON. You can measure the supply voltage at TP2 (TP3 is the power supply ground point). It must be Vpower – 0.7 V ( voltage drop of the polarity protection diode).

Connect the central pin of TRX PTT [IN] (J2) connector to the power supply ground (0V) keeping the previous ground connection. This imitates TX mode PTT signal. Both red LEDs on both boards must become OFF. Also the green led must be OFF. Now the boards are in TX mode.

The active PTT signal is ground (0 v). The PTT input voltage up to +0.7 v will activate TX mode. Higher positive voltages or open circuit will activate RX mode. This input will not have any impact to the PTT signal from TRX so other devices can be connected to the PTT output of the TRX.

When switching on and off connection of the central pin to the ground, the green led must be switched on with some time delay after the red LEDs are on. When AF Switch delay potentiometer (8) is in fully CCW position this delay is at its maximum.

These simple tests avoid any problems with cable connections and TRX PTT polarity and guarantees that the boards are working properly.

After these tests are completed, remove the test cables which connect grounds and central pins of TRX PTT [IN] (J2) and connect the Audio board with TRX with prepared TRX PTT cable (as described in the manual) . Do not switch on the TRX. Now the board must be powered and all LEDs must be ON. If the board is not powered that means that there is no connection between TRX ground and power ground of the Audio board. Remove the cable (RCA connector) from the switch board side and check with ohmmeter if there is short circuit between outer ring of RCA connector and TRX chassis.

The other reason might be that one of the terminals of the PTT output of the TRX is not connected to ground. In some TRX the PTT output is a relay contact and neither of its terminals are connected to ground. The Audio board senses the ground only through the PTT cable and this is a protection measure. In this case the ground sense wire in PTT cable must have additional connection to the TRX ground. Usually there is a ground pin in the TRX PTT connector. Make this connection inside the PTT cable connector . Any external ground connection will eliminate protection from “missing PTT cable”. The board TRX PTT input must sense ground only through the PTT cable.

Fig.3 The TRX/PTT input must get “ground” through the cable only. Connect one of the
terminals of the the PTT output of TRX to ground if it is not connected infernally. Make this
connection inside the cable connector. The idea is: if this cable is not plugged “missing PTT
cable” protection will be active and the switch device will not be powered.

Connect the TRX to the TX antenna but do not connect the Antenna switch module to the antenna and TRX. Switch on the TRX and set it in SSB mode. Push the microphone knob and enter TX mode. Now the board must enter also the TX mode and all LEDs must be OFF including Antenna switch module. If this is not so, check the polarity of the TRX PTT output. It must be 0 V ( ground) in TX mode. In some TRX this polarity might be set from the TRX menu or there are both polarities wired at the PTT output connector of the TRX.

If these test are completed connect the antenna cables to Antenna switch module as described in the manual and connect the SDR .