A SDR-receiver from the italian SDR developers community:

low-cost “Software Defined Radio” full coverage receiver for all HF bands, 50MHz (6m Band) and 70MHz (4m band), used with powerful software on the PC for multi-mode operation



This is a small and compact optional automatic T/R switch plug-in board for the PMSDR. Normally the antenna is connected to the PMSDR input. When it senses RF power on RTX, the antenna is connected to RTX input. There are available three operating modes: passive, manual and automatic mode. When the PMSDR is not powered, the transceiver is connected to the antenna to avoid transceiver damage.
This switch board is powered from the PMSDR and doesn’t require any external power supply!

Passive Mode
The SDR-software disable the PTT control unit. So the antenna is always connected to the transceiver, and you can use the software to switch the antenna between the PMSDR or transceiver.  This is the same condition when the PMSDR is not powered.
Manual Mode
Use the PTT control line of your transceiver connected to the optional PTT control line input. By grounding PTT, RTX. When the transceiver is connected to the antenna, the PMSDR RX input filters are disabled for better isolation. If PTT is open, the antenna is switched to the PMSDR RX input.
Automatic Mode
Don’t use the PTT control line. When the switch plug-in board  senses RF power on RTX input (HF-VOX), it automatically switches transceiver to the antenna, otherwise the antenna is connected to the PMSDR.

The audio output on Winrad/HDSDR can be muted automatically during the transmission. The PTT switch-off delay are software defined (PMSDR firmware V2.1.6 or higher), therefore it’s possible to change the PTT switch-off delay by the DLL (V3.2 rev5 or higher) interface:

Tipical configuration

Switch board block diagram

  •  HF Transceiver BNC-F Connector
  • Antenna BNC-F Connector
  •  PTT Control line 3,5mm jack
  • Frequency range: 0,1 -144MHz
  •  Maximum TX power: 100W
  •  RF sense threshold: <2W


SWITCH Board connections overview