Hermes Lite 2 SDR transceiver with transverter interface fitted.
Mike Lewis
This is an update of my SDR IF rig project built around the Hermes Lite 2 (HL2) SDR 5W HF transceiver based on OpenHPSDR. Apart from my Teensy SDR radio development work last spring, my last DIY(ish) SDR radio projects were the Flex SDR-1000 and a DSP-10 many moons ago.
I started off with a new HL2 last August comparing performance and learning and testing various SDR applications that work with the HL2 including some app debugging. I built 2 "controllers" based on the Raspberry Pi 4 CPU. My ultimate goal was to use one or 2 of these setups as VHF/microwave IF rigs. Recently I scored a 2nd barely used HL2. After testing it I transformed it into an IF rig with band decode outputs and Split TX and RX ports.
The HL2 IF rig:
The HL2 is an ethernet connected headless SDR transceiver so it uses a PC or Raspberry Pi as a "controller" to run the SDR applications. The only connection needed from the shack to this rig is ethernet. The modified HL2, transverters, amps, antenna switches, even rotator controller can be installed in a box outside the house, on your Rover or RV roof, or in the trunk. Only need the ethernet to the controller positioned where you want to sit, maybe on a picnic or kitchen table. Wired ethernet is preferred but can work in the right conditions.
I removed the N2ADR HF filter board and put in a 16 port i2c port expander module with 8 pins buffered with a ULN2803. The TxIF out comes from the input to the 5W PA section. The RxIF input is on the RX side of the TR relay. The PA can be disabled in software. The PA output is not connected to anything in this setup. There are ways to physically de-power the 5W PA stage but it should not be a concern.
There are PCB designs posted online that you could use but I already had the parts on hand so carved up a hunk of PCB and had it done in a few hours. I added code to the hermeslite.py test script (on the HL2 GitHub site) to operate either a 8 port (MCP23008 as used on the N2ADR filter board) or a 16 port (MCD23017) i2c port expander module. There is also code to use an external reference clock, typically 10Mhz, and to output a clock which could be a transverter LO if filtered appropriately.
The back panel presents Split IF with +16dBm on TxIF Out. Separate RX In jack. An attenuator will be used to get the 1mW my transverters are set to use. The DB9 has 4 buffered lines of the 16 available GPIO ports and the HL2 EXTTR (PTT Out) on pins 1-5. Will probably change out DB9 9 pin to a HD15 pin to better match the K3 connectors I have in use today. This was all I had for now. The SDRs apps all have user defined control for at least 7 IO lines. Can configure them any way you like, such as 4 BCD lines and use the others for antenna or rotator control. SDR apps and the keyer have many pre and post RF timing adjustments for sequencing. Keyer software like K3NG have many optional TX outputs for mutli-step sequencing.
Future HL2 IF rig changes:
1. HD15 connector Allows me to use a short straight through cable to the 5-Band transverter and plug in place of the K3 for easy swaps.
2. Build the 16dB TxIF out attenuator onto the PCB with SMD resistors
3. Add a 28MHz BPF if one is determined to be needed later.
It is also possible to connect to a VHF intermediate transverter to convert 144 and 432 for microwave transverter IF. A few early HL2 specific drop in transverters boards have been produced by forum members.
Pi Controllers:
For a controller I use a PC/tablet at times (desktop, or tablet) but most of the time I use the 2 Pi based controllers I built up.
Controller 1 is a simple Pi 4B CPU and Pi 7" touchscreen in a SmartiCase Pi Pro plastic case. I added some encoders to the bottom front apron area and connections on the back. Internally there is a USB sound card dongle for mic and line level audio out, audio amp, stereo speakers, and 12V to 5V 3A DC-DC converter. The CPU runs off and SD card. On the back are an external speaker jack with switch, mic connector, 12V power with power switch. I am using a standard radio mic or speaker mic. A USB GPS updates the time and grid location. Can run Hamclock also for lots of propagation and more location info.
Controller 2 is far fancier. It is in a Hammond extruded case that I had milled by Front Panel Express in Kent, WA. It uses an open source V2_mk2 bare PCB with IO expansion on board to handle up to 4 dual encoders with push switches, VFO encoder of various sizes, 16 key switches, and a soft power switch. The SDR app PiHPSDR by G0ORX specifically supports this PCB. I run the DL1YCF version of this app. Commercial versions (V12 and V2) is/was available from Apache Labs to work with their Anan SDR rigs. This PCB has an onboard 12V to 5V 3A DC-DC converter. Inside I added a 4 port USB hub, a USB SSD, USB sound dongle, 12V 3W stereo audio amp, mic jack, headphone jack, 3W Dayton stereo speakers, external speaker jack, CW key jack and HDMI output jack for a 2nd screen (can be touch also). Soon I will add a keyer described below to replace the USB sound card. Several app like WSJTX and logging programs do not work well on a 7” screen, or you have to take drastic steps to shrink the fonts and fake a large screen. The HDMI port lets you run larger screen as primary or 2nd screen. When you get to this level using a laptop with the USB keyer/Control pod might be smaller and simpler. You can skip the 2nd screen and just use a laptop to remote desktop in or use the network connection for the logging app, or even WSJTX.
Teensy USB Keyer:
I am running a prototype of a Teensy 4 based CW Keyer designed by the same person(s) that created/contributed to the HL2 project. It is almost ready for production (link). It is also a USB sound card and MIDI controller. It can key any rig as normal keyers do, but it can issue MIDI commands for PTT and CW paddles, or straight key, through a MIDI USB connection to most SDR apps so the HL2 can be located remote.
So far there are 3 CW keyer adaptations working. WinkeyTerminalEmulator, K3NG, and Hasak. The keyer receives the SDR app RX audio and passes it through to the headphone jack. The keyer sidetone signal is mixed into the RX audio (if using it that way) for virtually 0 latency sidetone.
I plan to add encoders and switches to make it a control pod for PC and Laptops, or even the small Controller. I will embed my smaller prototype keyer on a Teensy 4.0 inside my big controller. The production version is larger, has 4 pots and many jacks. I will house an box with encoders as the control pod I mentioned. Most keyer software have MIDI and/or serial command interface also so no physical controls are required.
This has been plenty of fun and has kept me off the streets for a few months now. In a week or 2 I plan to swap out my K3 IF rig with the HL2 IF rig and see how it all works out. It should pair up very nice with the 5-band transverter for VHF and microwave mobile ops this summer.
Mike
K7MDL EL87sm & CN88sf
hamw...@gmail.com
Hi Mike,
Very nice summary and photos of your project . It’s been fun and educational following your journey with the HL-2. The DIY hardware development and software application modifications to make it your own is very nice.
Your effort will definitely help me decide which direction and how I want to use my HL-2 going forward….lots of options. Thanks for sharing,
73,
Paul
WA9BTV
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