I never mentionned it on this blog or on the Electrolab’s Wiki, but some time ago, I built an Hermes Lite SDR. It’s a nice piece of hardware that Steve KF7O gave to the community. I said “gave”, because it’s a full open hardware, open software project.
This rig is a true DDC/DUC SDR, with a 12 bits/60 Megasamples ADC (an Analog Device AD9866 transceiver on a chip). It gaves me hours of fun, and could be used as a serious baseband bedrock for many extensions (transverters, power amps etc).
From a software point of view, this small and low cost SDR is fully compatible with the TAPR’s Hermes high-end system. It could be followed with any kind of Hermes client software, like OpenHPSDR GNUradio, GHPSDR3-Alex….
This is a snapshot of a dual RX config. of OpenHPSDR behind the Hermes Lite
The total cost of this system is around 100 to 150 $/€. The version I built (the one here described ) is allready deprecated, and will be soon replaced by a compact, monoboard 2.0 edition.
Anyhow, let’s take a short tour of this project
On top, the BeMicro SDK “usb key”, supporting the FPGA. The Hermes lite itself is the small green board located on the right of the BeMicro, followed by a simple output board (two transformers winded on binocular).
On the lower side, a bandpass filter (tcheb) originally designed for the Softrock Mobo 6.3 project. This bandpass filter is used in transmit mode only. Different receive tests show no difference between an “barefoot” Hermes Lite and a filtered one.
The bandwidth of each filter has been enlarged to lower insertion losses
On the right of the case, a 10 W power amplivier (a TAPR’s original Pennywhisle).
As the Hermes Lite is note able to directly drive the Pennywhisle, a 20 dB/1W driver, using a single operational amplifier (OPA2677) is inserted between the rig and the amp
This home made amp has been designed to fit into low profile machined cases (former MCL 3dB hybrid couplers sold a few $ on eBay)
The pennywhisltle itself is mounted on the rear panel. A better amp, like the 20 W G6ALU (particularly VK3PE Glenn’s version) would have been more suited… but I keep this amp for the H.L. 2.0
So far, this combination gives good results and can drive a 300 W PEP power amp without problems
On the other side of the case, a CW Curtiss Keyer (former MFJ keyer), the linear power supply (as Steve said : “lot’o heat”… but with a good and silent fan, it works as advertized.
The brown board with 5 connectors is the switching interface between the Hermes Lite and the filter board
This is a quick and dirty hack with an ULN relay driver.