TRX-SDR Switch Kit

This hamradio kit allows your SDR and Transceiver to simultaneously use the same antenna, with PTT from the Transceiver (TRX) used as a control signal

Table of Contents

Key Kit Features

  • Permits transceiver and SDR to share a single antenna
  • Allows concurrent SDR waterfall (panadapter) and transceiver reception
  • Select between transceiver and SDR audio during receiving
  • Audio delay click circuit to avoid audio clicks  
  • Separate modules (audio board and antenna switch)
  • High quality connectors

The purpose of the Kit

The main purpose of this Kit is to allow your Transceiver (TRX) and Software Define Radio (SDR) to use the same antenna. During receiving both the SDR and the TRX are connected to the common antenna. When the TRX starts transmitting the SDR is disconnected and grounded.

The Kit also manages the audio paths. During transmission, the TRX audio is always selected, thus avoiding the effects of the audio delay from the SDR. During reception the user has the option to switch between TRX and SDR audio. The delay, with which the SDR audio is switched back, after the transmitting stops, can be regulated. This is important, since this delay depends on the specific SDR software and hardware being used.

For other possible use cases please check the technical documentation page.

Main features

  • Allows the SDR and the TRX to use simultaneously the same antenna. In receive mode the SDR is connected to the antenna, whereas during transmission it is disconnected and grounded. The TRX is permanently connected to the antenna.
  • In case a separate receive antenna is used, the SDR is fully protected during transmission.
  • The Kit consists of two separate boards:
    • Audio Switch – also responsible for controlling the ANT Switch.
    • ANT Switch – It is RF shielded and contains the antenna relay and receive input limiter.
  • PTT from the TRX is used as a control signal*.
  • During transmission, the audio signal from the SDR is muted and the audio from the TRX is selected.
  • Has a variable audio delay circuit to avoid audio clicks when transmitting (due to SDR signal delay). With the potentiometer you can adjust the delay for the SDR audio after transmission ends.
  • Option to switch between TRX and SDR audio during receiving.
  • No AF ground loops. There is no common ground between TRX and SDR audio within the kit.
  • High quality connectors are used.
  • Double fault SDR input protection in case of antenna relay dysfunction. There is a high power input RF limiter for high currents keeping the input voltage of the SDR at safe levels. This protection can withstand full TRX power.
  • Protection against disconnected TRX PTT cable.
  • Protection from missing power supply.
  • Recommended to be powered from the 12 V power source used by the transceiver (i.e. common ground is needed).
  • Over current protection with resettable fuse.
  • Can control additional external relays (up to 200 mA current) synchronized by the TRX PTT signal – e.g. for PA control, TX antenna detuning, receive antenna switching, station automation etc. This approach avoids RF ground loops when multiple devices are used.
  • The kit boards are tested and ready for use.

* A standard “TX transmits” output from the TRX is used as a control signal. This signal has different names from transceiver manufacturers: SEND; TX-GND; T/R-LINE; Ground-on-Transmit. Further on we will refer to it as TRX PTT. This signal can be used also by other equipment connected to the TRX e.g. power amplifier (PA).