The SDR concept is a flexible approach to building amateur radio equipment. The photo illustrates the multi band SDR rig at my operating position at home. The photo at the bottom of the Home page (Home Page) depicts an example of some of the same equipment configured for as a rover station for 10 GHz operation. The flexibility of this system can be seen from the arrangement of the front panel coaxial patch cables for 2 meter operation at home compared to the coaxial patch cables that link the SDR transceiver module with the 10 GHz transverter module. This SDR system covers 160 meters through the 24 GHz amateur bands. Let us review some of the big takeaway features of such and SDR system before I describe in detail the modules in the photo.
- The DSP software for each SDR and for each band in the entire system is authored in GNU Radio.
- The DSP’s are basically the same for each SDR and for each band. The ‘RF Parameters’ for the Source (receiver) and Sink (transmitter) are the only DSP parameters that need changing. Those parameters vary depending on the desired frequency(s) of operation. To change bands, the band range specific DSP to go on the air. The DSPs are simply data files on your computer that can be selected and executed at will.
- The DSPs are authored to be mode specific. Mode specific DSP’s reduce the complexity of the flowgraph representations that allow multiple modes in a single flowgraph. For instance, the ‘multi-mode’ CW/SSB transceiver, the NBFM transceiver, the ‘digital mode’ transceiver, the AM mode transceiver DSP’s are the same on any band. To change modulation modes, close the .grc mode file you are currently using and execute the .grc file for desired mode.
Referring to the photo, the station can be divided into two parts: the HF equipment below the shelf and the VHF through Microwave equipment on top of the shelf. The HF equipment consists of the small white box, an Ettus N200 SDR transceiver, the small black box, an outboard CW keyer, and the large white antenna rotator box. Behind the shelf and out of sight is the RF Interface for HF. (see: RF Interface for HF) The desktop computer and screen located to the right side of the photo are not visible,. The HF station covers 160 through 10 meters at the 100 W level, using any modulation mode. The the Ettus N200 is an example of an ‘advanced’ or ‘state of the art’ SDR. This state of the art SDR provides direct conversion to baseband for the entire HF spectrum with high speed A/D and D/A converters. The quadrature mixer implemented in the Field Programmable Gate Array (FPGA) determines the frequency of operation via commands from the software host via Ethernet. (see: Advanced SDR a description)
The VHF through Microwave equipment lineup is more complex and is confined to the top of the shelf. On the left edge, resting on the shelf, is the VHF through Microwave Ettus SDR transceiver packaged in a black and gray plastic enclosure. The SDR transceiver is an Ettus B210 dual transceiver SDR that offers single conversion operation between 50 MHz and 6 GHz. This state of the art SDR has an architecture similar to the Ettus N200 described above with the addition of an integrated RFIC that performs the single conversion step from microwave to baseband. Barely visible in the center of the transceiver front panel are the SMA connectors for the integrated microwave T/R relay. This relay is shared with all modules to switch antennas and transceivers for the entire system (see VHF / Microwave RF Interface ). On top of the transceiver sits the 10 GHz and 24 GHz transverters packaged together in another black and gray plastic enclosure. In the center, and to the right of the transceiver/transverter stack, are the aluminum boxed home-brew power amplifiers with coax connectors for the VHF and UHF bands (see VHF-UHF Power Amplifiers). Further to the right are the rotator controller and the antenna selector for the VHF antenna mast.
- The modular approach is intended to promote flexibility of operation, permit evolution of the system to respond to new ideas, and to accommodate to use on additional bands such as 47 and 79 GHz.
- The hardware is designed to accommodate to the unique amplifier and antenna combinations for each band, and for fixed home station or rover operation.
- Band change re-configurations are accomplished by patching either the SMA or BNC coax cables to the appropriate module with the common T/R relay. This patching arrangement is similar in concept to the early 20th century telephone switch board system.