That it is possible to create a modern SDR with small dimensions proves the SQUARE SDR. Its construction includes a printed circuit board with dimensions 100 x 100 mm, on which the receiver is integrated together, transmitter, power amplifier, filtre HPF a LPF.

René OK1XTG came up with the idea to combine the existing Hermes-Lite SDR transmitter project 2 (HL2) with HPF and LPF filters for amateur radio bands from 160 do 10 m – N2ADR

Mounted SQUARE SDR printed circuit board
Mounted SQUARE SDR printed circuit board

Basic specifications of the SQUARE SDR

  • Supply voltage 11 – 15 VDC
  • RX frequency range 100 kHz – 30 MHz / TX 1,8 – 30 MHz (amateur bands 160 – 10 m)
  • Integrated HPF and LPF filters (N2ADR)
  • RF output power max. 5 W
  • power consumption when receiving without the fan on approx 3,6 W
  • transmission power (CW 5 W) without fan on approx 18 W
  • 12-bit ADC/DAC
  • Gigabit Ethernet
  • External frequency reference I/O
  • LED indication of the relay on the board
  • SWR meter (PSV)
  • Internal fan 80 x 80 mm. From the PCB version 05 with independent control, which does not conflict with PWM Band Volts
  • Integrated TTL 3V3 voltage serial interface including pull-up resistors on the data lines. Hardrock-50 connection (DB-9 ACC connector on the rear panel)
  • Integrated SMA connector (RX) to connect the probe “Pure Signal”
  • Protection and indication of incorrect supply voltage (undervoltage) or incorrect connection (opposite polarity)
  • Full SW compatibility, GW and functionality with Hermes-Lite 2
  • PCB 4 layers, dimension 100 x 100 mm
  • one-sided SMD mounting
  • total external dimensions in the box 126 (š) x 46 (in) x 110 (h) mm
  • weight approx 490 g

Mechanical construction

SQURE SDR mechanical construction
SQURE SDR mechanical construction

The basis of the mechanical construction is an aluminum profile with dimensions 120 x 40 x 98 mm and wall thickness 4 mm. Holes for mounting side panels, circuit boards and fan are machine drilled into the body. There are plastic parts on the front side of the aluminum profile, into which the side panels are inserted. The side panels are realized as printed circuit boards with high-quality printing. Copper is left on the inside of the PCB side panels, which is electrically connected by four screws in the corners to the aluminum profile. All this ensures sufficient shielding for the operating frequencies of the SDR itself. The entire structure also provides sufficient cooling for continuous operation.

Alternative power connector

Alternative power connector
Alternative power connector

For permanent installation in harsh climatic conditions, an alternative was developed to fit the printed circuit board with a more robust connector for the supply voltage (P2). The type of connector used is PTR STLZ1550/2G-3.81-H-GREEN with its counterpart PTR AKZ1550/2-3.81-GREEN.

Commissioning of SQUARE SDR

For maximum and optimal use of the SQUARE SDR hardware, perfect knowledge and setting of the operator program is required (consoles), which controls the SQUARE SDR. If not properly set up and operated, some parts of the device may not work properly or at all. SQUARE SDR is compatible with all software supporting the openHPSDR protocol 1. Thetis is probably the most elaborate at the moment.

In the utility (console) the SQUARE SDR is selected and connected as “HERMES LITE”, “Hermes-Lite”. Therefore, all published settings for HL2 can be used.

SQURE SDR in operation
SQURE SDR in operation

This SQUARE SDR design was not created to create a cheap Hermes-Lite clone 2, but with the aim of improving, simplify and overall streamline the single-purpose design. So it's not a kit. The original Hermes-Lite concept 2 brilliantly designed by Steven KF7O and he has my admiration for that.

If you want to order SQUARE SDR, visit https://www.wideservis.cz/square-sdr/

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