SDR Hardware information.
There are two basic types of Software Defined Radio (SDR) rigs that are popular these days. In addition, there are some SDRs based more traditional radio design (superhets, direct-conversion, etc).
The first of the newer SDR design is typically a lower-cost solution. It is based on the Quadrature-Sampling-Decoder (QSD) for receive, and Quadrature-Sampling-Encoder (QSE) for transmit. The QSD/QSE has been the more popular design to this point in time.
The second type of SDR radio design is based on converting the RF into digital data as early as possible. While there may be preamps, attenuators, or other devices in front ot it, the first major part in a receiver is an analog-to-digital (A/D) converter. In transmit, the modulated digital data is sent directly to a digital-to-analog (D/A) converter to create an RF at the transmit frequency. The output of the D/A is generally amplified and filtered. Most of the hard work is accomplished in software, using DSP techniques.
However, unlike the QSD, additional software/firmware (usually in a very fast IC) is used to translate the RF data samples from the A/D to a lower quantity of samples that the computer running the DSP software can work with. This process uses special digital filtering and down-sampling, and the implementation is called a Digital Down Converter (DDC). In transmit, a similar but mirrored method is used to up convert the modulated signal up to the RF frequency, which the D/A then converts to an analog waveform.
(the above needs some work - and maybe moved to a theory page)
QSD/QSE SDR HARDWARE
Some of the most popular SDR hardware devices are the various SoftRock kits available from Tony Parks. While Tony does not maintain a list of products on a web site, his latest offering are usually shown at the SoftRock40 Yahoo group web site. This is a GREAT group to join for general SDR information as well. SoftRocks are typically small PC boards and associated parts kits available for a low cost, and operate at various amateur HF bands. They translate modulated I & Q IF frequencies in the audio range (normally from computer sound cards) to/from the HF band of interest using QSDs and QSEs. Tony keeps updating his product line with new inovations, so it's hard to track here the exact models. A separate page has been set up for this reason: Tony Parks Order website. Cost is low, construction is fairly easy, and results are excellent for the price. WB4JFI has several , and HIGHLY recommends Tony's kits for a first SDR project.
The Flex Radio SDR-1000 is probably the defacto standard of SDR hardware. It was for sale for a few years, until early 2008. A newer set of radios have replaced it, first the Flex-5000, then the Flex 1500 and 3000. The Flex-5000 comes either as just the SDR hardware, or an all-in-one box, including the host computer baord.
A series of articles on SDR hardware using QSDs and QSEs in QEX Magazine was based on the original version of the SDR-1000. The original SDR-1000 was made up of three PC boards bolted together (a BP filter and 1/2W Tx PA, a DDS and QSD and QSE, and a power supply and interface board). After a time, a fourth (RFE) board was added to the stack, which held a receive preamp, a better Tx PA, better filters, and a set of shift registers to expand the control I/O from the host computer. The newer Flex-5000 uses a firewire connection to the host computer for both control and IF signals.
A 100W HF amplifier board, an automated antenna tuner board, a 2M transverter board, and an enclosure were also available. The original control interface between the SDR-1000 and the host computer was an advanced parallel (printer) port, but a special USB adaptor was added to the product line. The SDR-1000 relied on sound cards to interface the QSD/QSE IF signals between the SDR and host computer.
The Flex radios all operate from the 160M to 6M ham bands, and include a general coverage receiver as well. PowerSDR under Windows is the most popular software package used with Flex radios.
The SDR0001 from SDRTech is from India and very similar in design to the Flex-Radio SDR-1000 (it was based on the original QEX articles). It was designed to fit onto a single PC board, and some improvements were reportedly made. NOTE: THIS MANUFACTURER SEEMS TO HAVE GONE OUT OF BUSINESS AFTER SOME ISSUES WITH ORDERS AND DELIVERY.
SDRTech has recently announced a WonderRadio Pro, whch includes a single-board-computer in the same box, for a one-box solution. They have also announced 10W and 100W amplifiers.
While the SDRTech radios are close enough to the SDR-10000 that they can use the same PowerSDR software, SDRTech may be providing a specialized version in the future.
The KDG-SR100 is another virtual-clone of the Flex-Radio SDR-1000, of German manufacturer. It was designed around the QEX articles, onto a single PC board. There have been some comments that the SR100 specs may not quite match the SDR-1000 itself. It is close enough to the SDR-1000 that it can use the same PowerSR software.
David Brainerd, WB6DHW is a lot like Tony Parks. He designs and sells circuit boards (and sometimes kits) more to support the hobby than to make a huge profit. David's designs are often a step up from other SDR devices. For example, he has one board that contains a 0-200MHz DDS, USB PIC controller, buffers, and QSD circuit that often receives beyond 8MHz. Some of his offerings include:
Prototype matching QSE board
HF bandpass filter with six filters and electron switches
A 12V to 24V power supply for RF power amplifiers
UHF SDR board
High-Speed USB board using an FX2
Most of these boards are around $8 each. Check his web site for the latest offerings. In addition, Art (callsign), can provide parts kits for some of David's boards.
David's designs are often discussed in the dds_controller Yahoo group.
Elektor magazine produced an SDR receiver design in their May 2007 issue. They sell copies of the magazine, bare PC boards, or complete kits (approx $141)of this design. It covers 150kHz-30MHz, and uses a USB connection to the host computer. It uses a QSD, and a programmable oscillator to cover the complete frequency range. While it does not have any band-pass filters on the input, it does have a switchable fixed attenuator.
DIRECT CONVERSION RADIOS (DDC and DUC)
SDR-14 & SDR-IQ RECEIVERS
QS-1R RECEIVER (AND COMING QS-1T EXCITER)
USRP and USRP2
Dr. John Schwacke has designed an RF A/D board that plugs into a Digilent Nexys2 FPGA board, which includes an 30MHz LP filter, variable-gain amplifier (VGA) (AD8331), and a 12-bit Burr Brown (TI) PGA/ADC/DDC/DAC converter (AFEDRI8201). Some basic FPGA and Linux software has been created to allow this board to receive HF, 2 meters, or FM broadcast, with the GNU Radio package under Linux. A simple spectrum display is also avaialable under Windows. This board is just now being tested. For more information, visit: Dr. John Schwacke's Web Site. AMRAD IS VERY INTERETED IN THIS LOW-COST DESIGN. The FPGA development board can cost about $120, and the parts for John's board cost about $80. While 12-bits of A/D may not allow a high dynamic range, the use of bandpass filters, along with the variable-gain amplifier may mitigate some dynamic range issues.
This board is a direct digital conversion system for HF, covering 0-30MHz. By bypassing the LP filter and VGA, this board has been used to receive commercial FM broadcast stations, as well as 2 Meter repeaters, using subsampling techniques. The use of bandpass filtering and optionally an inexpensive preamp helps with 2 Meter reception.
Software for this board is in its infancy at this time. The FPGA only contains a couple of FIFO's for I & Q sample data, and a few control signals to the hardware. More on this effort as it is developed.