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Making Amateur Radio Connections

Hermes Lite 2

#post #SDR #HF #Hermes-Lite #OpenHPSDR

The Hermes-Lite 2 (HL2) is a low-cost, open source HF SDR transceiver. This is a truly fantastic radio it competing head to head with the Flex radio. The whole project – hardware and software – is fully open source, led by Steve Haynal (KF7O). Although this radio has been around for years the community support is poor. My hope is this post will help document what I’ve found for my own use and maybe help others.

I purchased mine from MakerFabs along with the N2ADR filter board and IO board.

Hardware

The hardware is based on the Analog Devices AD9866 broadband modem chip and an Intel Cyclone IV FPGA, using the OpenHPSDR protocol over Ethernet. There is no audio output on the HL2 itself. Your computer runs the SDR software and handles all audio. This is pure network SDR – the radio sends raw IQ data over Ethernet.

A complete radio has a stack of boards, all connecting through a 20-pin header inside the enclosure:

  • Transceiver - The main board with the AD9866, FPGA, Ethernet, and 5W PA. Has three RF ports: RF1 (main RX/TX), RF2 (RX only), and RF3 (low power TX / Pure Signal input). Front panel has a 3.5mm jack for CW.
  • N2ADR Filter Board - Designed by James Ahlstrom, N2ADR (also the author of Quisk). Mounts directly on the HL2 via a 20-pin connector. Has 6 low pass filters covering all HF bands for transmit harmonic suppression, plus a high pass filter at 3 MHz to kill AM broadcast interference on receive. Includes SWR bridge for forward/reverse power measurement. Thanks James.
  • IO Board - Also by Jim Ahlstrom. Mounts above the filter board. Uses a Raspberry Pi Pico for frequency-based automation – controls amplifiers, antenna switches, transverters, fans. Has 8 CMOS outputs, low-side switches, and SMA connectors for separate RX and Pure Signal inputs. This board needs a 1x3 pin header soldered to the main board for 3.3V, GND, and VSUP.
  • Plus Board - Third party add-on (not affiliated with the HL2 project). Adds headphone and microphone jacks, CW sidetone, IAMBIC keyer, and Icom AH-4 ATU control.

Software

The hardware is the easy part. You’ll need a program on your computer to use the hardware. All of these “talk” over ethernet using the OpenHPSDR protocol. No sound card, no USB – just a network cable.

  • Thetis - Windows. Fork of PowerSDR with HL2 support. (My recommendation)
  • SparkSDR - Free, runs on Windows, Mac, Linux, and Pi. Good for multi-band reception with multiple receivers.
  • SDR Console - Windows only. Professional interface. Has CW side tone via PC audio.
  • Quisk - Open source, Python, runs on Linux, Windows, and Raspberry Pi. By Jim Ahlstrom (N2ADR). This is the one I use most. It can update HL2 gateware and change the MAC address.
  • piHPSDR - Linux / Raspberry Pi. Includes Pure Signal and WSJT-X CAT control.

You can find more posts here about configuring this software and others.

Audio - Virtual Cables

Your SDR software (above) connects your computer’s microphone and speakers (Headset) to the HL2. You select the sound card device in the SDR software.

Because no physical audio cables are used you’ll need virtual audio cables to connect digital modes like FT8 to your SDR software. You connect the digital software’s output to the input of a virtual cable (VC-A IN) and the output of the virtual cable (VC-A OUT) to the input of the SDR software. Then connect the digital software input to the output of a second virtual cable (VC-B OUT) and the cables input (VC-B in) to the SDR software’s output.

  +------------------+        Virtual Cable 1       +------------------+
  |                  |  RX audio                    |                  |
  |  SDR Software    | >--------------------------> |  WSJT-X          |
  |  (Thetis, Quisk, |                              |  JS8Call         |
  |   piHPSDR, etc.) |  TX audio                    |  WSPR            |
  |                  | <--------------------------< |  fldigi          |
  +------------------+        Virtual Cable 2       +------------------+

Both programs run on the same computer. The virtual cables replace what a physical sound card and radio interface would normally do.

Windows

Install VB-Audio Virtual Cable. The free version gives you one virtual cable (VB-Audio Virtual Cable). If you need more pairs, the paid versions (A+B, C) add additional cables.

Linux

Use PulseAudio or PipeWire to create virtual sinks. No extra software needed – it’s built in.

Create two virtual sinks (one for RX audio, one for TX audio):

pactl load-module module-null-sink sink_name=sdr_rx sink_properties=device.description="SDR_RX"
pactl load-module module-null-sink sink_name=sdr_tx sink_properties=device.description="SDR_TX"

Then in your SDR software (Quisk, piHPSDR):

  • Set RX audio output to SDR_RX
  • Set TX audio input to SDR_TX.monitor

In WSJT-X or JS8Call:

  • Set audio input to SDR_RX.monitor
  • Set audio output to SDR_TX

To make these persist across reboots, add the pactl commands to your startup scripts or add the modules to /etc/pulse/default.pa.

More Power - Xiegu XPA125B Auto Band Switching

The HL2 IO Board can drive a Xiegu XPA125B amplifier with automatic band switching. When you change bands in your SDR software the amplifier follows automatically. This uses the IO Board’s PWM band voltage output on its DB9 connector. Credit to M0AWS and Ramon (KP4RX) for documenting this.

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