What an Amazing Little Kit!
The Hermes Lite 2 (HL2) is a fully Software Defined Radio (SDR) transceiver based on a broadband modem IC. The IC has RF amplification and a 98Mhz A/D converter that allows digitizing the antenna RF signals directly, capturing the entire HF band from 160-10M (1.8Mhz-30Mhz). I purchased my kit through MakerFabs. I also purchased the case and the low-pass-filter board. The kit arrived quickly and went together equally fast.
There are many good SDR programs out there (for Windows, Linux and MacOS), but I have chosen to use HDSDR Thetis as my “Rig”.
Thetis contains all the magic that it takes to accept a stream of A/D readings over TCP/IP, and demodulate them to create the audio and user interface experience of a real radio. It is also responsible for the reverse, modulating the audio and streaming it back to the HL2 for transmission. The HL2 uses a Field Programmable Gate Array (FPGA) to manage the sampling and communication over ethernet, as well as provide multiple VFOs through Thetis. The HL2 can transmit 5W of RF and has the band-selectable low-pass filtering required to be a good citizen.
What really impressed me was the overall performance of HL2. The receive sensitivity is incredible considering the price. When paired with Thetis, you have all the rig control to connect in other applications such as WSJT-X, JS8 Call, VaraC, FLDigi, and the like. Note: Winlink does not seem to work (at least so far) due to some timing issues and inherent delays in the audio — which comes with SDR.
I found that this little rig was almost perfect for use with our RV on our outings.
Almost.
For the Lack of a Tuner
Once I had a chance to get familiar with the HL2 I did what most Hams do — I modified it.
The goal was to embed an automatic antenna tuner (ATU) into the case of the HL2 to arrive at a fully functional portable rig in one tiny package. I decided to purchase an ATU-100 which are readily available from eBay and to begin sizing things up.
Step 1.. Does it work?
So before committing to packing it into the shell I hooked up the ATU and tested it outside the shell. This quickly got me excited because with 2W or so, the ATU has no issues tuning up.
Step 2.. Jamming it in
Removing the top shell of the HL2, it quickly became apparent that the ATU would nest down into the electronics of the main board and low-pass-filter (LPF). There was a small collision. The jumper block from the kit that connected the main board to the LPF is about 1/8-inch too tall to allow the ATU fully within the shell. This was solved by purchasing some jumper blocks from Amazon (like the ones you find on PC motherboards and Arduino kits). Once nested I was able to measure the port positions and create a temporary front and back panel to hold everything into place. Double sided tape was used to stabilize the board vertically, and the SMA connector and the required cross-cabling on the rear, affix everything to prevent movement of the board.
The OLED screen does fit into the front, but it is incredibly tight and required care to prevent damage to the display or the HL2 main board. There is a programming connection that interferes with the display mounting in my solution, but I was able to bend the leads a bit and insulate the pins to prevent shorts.
Step 3.. Final Touches
To finalize the packaging project, KiCAD was used to create the Gerber files that a PCB shop would use to make circuit boards. I use JLCPCB regularly for projects and thought this would be a great time to try their Aluminum PCB materials and processes. The front and back panels were combined onto one PCB to save cost. JLCPCB produced 5 sets like this for $7 US + $25 shipping. The panels arrived in a week!
Using a bandsaw, I separated the top and bottom panels and then filed the cut-edges smooth. The end result was not bad! The aluminum panels add to the total heat dissipation and look like they’ve always been there. (I covered the unused SMA connectors with 3D printed caps to prevent damage.)
If I wish to take the ATU out of circuit, I can plug the antenna into the new “TRX1” port. Otherwise, I jumper “TRX1” to “ATU” and the output is now “ANT” as pictured below.
I really do enjoy this little rig! It is inexpensive, and capable! If you would like the KiCAD files for the faceplates, and cap cover STL files, they are available for download from ldocull/HermesLite2-ATU (github.com).
73! de WR9R