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 2-in-1 optional automatic T/R switch and tunable preselection filter plug-in board for the PMSDR. There are two filters on this board:

Main features:

  • No external power required – low power cosumption design
  • Build-in antenna switch (Switchboard)
  • Passthrough for Broadband input (to use with external filters)
  • Filter 1: is a software controlled, 13-bit digital tunable band pass filter from 0.3MHz up to 7.3MHz ! (take a look at this video (vertical scale 10dB/div) for the frequency response and how it work…)
  • Filter 1: frequency response @ 40m, 80m, 160m, MW, 600m bands (vertical scale 10dB/div)
  • Filter 2: a bandstop filter (Notch) for the FM broadcast band (88MHz – 108MHz) (see the filter response)
  • Reed relays for the filter switch circuit (no PIN diodes)

Price / Availability

The tunable preselection filter have a high off-band attenuation, especially at 3th harmonic frequencies. This filter is therefore particularly suitable for the listening on the lower HF, MW and LW band.
The tuning process is done full automatically by the DLL or firmware. Therefore is possible to use the filterboard  also with the Si570-USB mode. The DLL permit also to tune this filter manually.

Furthermore, this board have also a build-in automatic T/R antenna switch, which permit to use a transceiver on the same antenna with the PMSDR (like the Switchboard): 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.
The Filterboard is powered from the PMSDR and doesn’t require any external power supply!

The assembled Filterboard (77 x 92mm)

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 a 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 input.

The audio output on Winrad/HDSDR can be muted automatically during the transmission. The PTT switch-off delay are software defined, therefore it’s possible to change the PTT switch-off delay by the DLL  interface:

Tipical configuration

Filterboard block diagram
Tecnical data (with PMSDR):

  • Insertion loss (ANTENNA-PMSDR broadband) : about 0.15 dB
  • Tunable filter frequency response: look at this video (vertical scale 10dB/div) – Frequency response @ 40m, 80m, 160m, MW, 600m bands (vertical scale 10dB/div)
  • Tunable filter IP3 response: coming soon
  • bandstop filter (Notch) frequency response for the FM broadcast band (88MHz – 108MHz)
  • Power supply: USB (+5V) – min. 40mA, max. 170 mA
  • PMSDR firmware version requirement : V 2.4 or higher
  • ExtIO-DLL version requirement : V 3.8r0 or higher

Switch preliminary technical data:

  • Transceiver Connector: BNC-F
  • Antenna Connector: BNC-F
  • PTT Control input: 3,5mm jack
  • Frequency range: 0,1 -500MHz
  • Maximum TX power: 100W (UHF 50W)
  • RF sense threshold: <2W


FILTERBOARD connections overview