Setup when using a Power Amplifier

Technical documentation

If you are going to use your TRX-SDR Switch with a Power Amplifier (PA) or other devices which use the TRX PTT, please make sure you read and understand the text below. If something is not clear or you have additional questions, you are welcome to contact us.

Warning: The “TRX PTT missing” protection will not work, if the Audio Switch TRX-PTT [IN] gets ground connection through other connected devices (PA in this case) and at the same time the TRX PTT cable is not plugged to the TRX (see Fig.3). This is the reason why a particular wiring should be used (as shown on Fig.1 and Fig.2).

Figure 1 is showing correct wiring when the TRX-SDR Switch is used with a Power Amplifier (PA). Notice how wire-1 (in grey) is connected to the ground nut of the transceiver (and not directly to wire-2)! This guarantees that when the cable is unplugged from the TRX PTT the TRX-SDR Switch will remain always in transmit mode.

Note: Actually, wire-1 is not strictly needed as the PA gets TRX ground from the coaxial cables.

Figure 1 – Correct wiring when a PA is used.

On Figure 2 is shown the same correct wiring but using a more technical diagram. Anyway, it is visible that if the cable is disconnected from the TRX PTT, the Audio Switch board (TRX PTT [IN]) will not be connected to the TRX ground and the module will remain in transmit mode.

Figure 2 – Technical diagram of correct wiring when a PA is used.

Wiring shown below on Fig.3 is incorrect. Notice how wire-1 is directly connected to wire-2. If the cable is now disconnected from the transceiver, the “TRX PTT missing” protection will not work because the Audio Switch board will get TRX ground from the PA through wire-1. This will lead the Audio Switch box to “think” that it is properly connected to the transceiver and consequently enable receive mode. Now, if the TRX starts transmitting the TRX-SDR Switch will remain in receive mode!

Figure 3 – Incorrect wiring when using a PA.