UHF-Satcom.com - A brief review of the RF-Space SDR-IQ software defined radio                                                (04/03/2010 12:08:52 -0000)

SDR-IQ bottom PCB view (serial number 1)

SDR-IQ top PCB view

The first thing to say about the SDR-IQ is 'WOW!'. This represents about the best $400 (promotion price) spent in recent years!

Having heard about the possibility of a low cost SDR, UHF-Satcom.com contacted RF-Space indicating interest in this device when it appeared on the market. The specifications are as follows:

On receiving the unit, the compact size of the PCB is immediately apparent. It is also very light weight and therefore suitable for use in portable situations, such as microwave contesting or remote monitoring expeditions. The SDR-IQ runs from the +5 volt supply out of the USB2.0 socket on the PC, so does not require an external power supply. The PCB is fairly dense in terms of components, with not a lot of spare board space. There are two positions for PCB mount SMA sockets, one is for an external oscillator (J6) and the other for RF Input (J4). J4 is enabled by fitting a SMA socket, and moving R6 to the R5 position. This also disables the use of the BNC socket. On the front panel are LED's indicating power, capture and clip. The clip LED illuminates when the input RF is of such a high level that it overflows the ADC registers. The SDR-IQ also has an RS232 port which can be used to control a receiver, when the SDR is connected to the IF output socket. This permits tuning over a greater range - the SpectraVue software supports the Icom R7000/R8500 and AOR AR-5000 receivers "out of the box" but also has the facility for custom receiver configurations. The RS232 port is great where you have a remote controlled system, as all the communications to / from the target receiver are done over the USB bus, along with the IQ FFT data. Using the SDR-IQ as a stand-alone allows you to tune over the 100Hz to 30MHz spectrum.

Installation of the software is straight forward. A simple download and installation of the SpectraVue software from the MoeTronix website and the system is operational. A USB driver has to be installed before the SDR-IQ can be used, but this is also included with the SpectraVue software suite. When the SDR-IQ is connected to the USB port, there is a small amount of clicking from the internal filter / attenuator switching relays, presumably as the micro boots, or as part of a self test. The FTDI drivers for the USB chip are to be found in the "\program files\SpectraVue\SDR-IQUSBdriver directory. On firing up SpectraVue, the operation of the unit somehow seems cleaner than that of the SDR-14, but its presumed this is psychological since the unit is new etc. The FFT response in 190KHz bandwidth mode is very fast when used with nominal bin bandwidths such as 24Hz. The SpectraVue offers nice facilities of FFT averaging which is useful for stable carrier detection such as that from microwave beacons etc. FFT bandwidths can be set anywhere from 5KHz to 190KHz wide. A variety of demodulators is also available giving AM, FM, SSB and CW modes, all with infinitely variable bandwidths.

Firmware details for the SDR-IQ

Running an FFT Software Defined Receiver such as the SDR-IQ certainly opens up a whole new world of radio monitoring. It is particularly useful when looking for very weak signals, for checking out satellite transponders, and for looking at modulation schemes that exceed the standard 3KHz SSB bandwidth. Radio data mode software will hopefully soon make use of the SDR-IQ device for direct IF input, allowing faster and more complex radio data modes to be demodulated, overcoming the limitation caused by receiver IF bandwidth and SSB filters. Typical applications are Inmarsat data modes, and also Intelsat type PSK modems up to about 128Kbps. SDR programming will eventually replace conventional receiver construction - new modes and features can be created in the software domain with no modifications needed to the hardware. The SDR-IQ in particular also offers some interesting possibilities at VLF since its lower frequency limit is 500Hz. Experiments are planned with Ultrasonic receivers connected to the SDR in order to listen to Bats etc ;-)


Case type 1455N1601 from Maplin Electronics (UK)

Above left is the drilling template to help with mounting the PCB. The image should be printed at 300dpi such that it comes out at 95mm wide. The four holes at the corners should be on 83mm centres. Above right shows the SDR-IQ mounted in an suitable case - this being type 1455N1601 available from Maplin Electronics in the UK. The case has a series of horizontal slots each side, intended for PCB's. The SDR-IQ is mounted on an aluminium plate which slides into the slots. The front and back panels are then milled out to accommodate the LED's and connectors. The pictures can be clicked for full resolution. The picture below shows the completed unit.

The image below shows the FFT from an SDR-IQ connected to the 10.7MHz IF output of an AOR AR8600MK2 receiver. The vertical line is from a Geostationary satellite at 12 degrees West DSCS-III and the Doppler carrier is USA-81 crossing the beam. (Tnx to xBr for the image)

This next picture (thanks to xBr) shows a sun transit on 2257MHz. The antenna is a 1.2m diameter dish with helix feed.

Initial impressions are that this is an excellent investment - everyone who monitors satcom or radio in general needs to have a FFT capability such as this. Why listen to 3KHz wide audio when you could also be watching 190KHz of RF in real time?

Click here to order your SDR-IQ now!!  BTW please tell RF-Space that you read about the SDR-IQ at UHF-Satcom.com !

If you are interested in seeing what other users think of this SDR, its well worth joining the SDR-IQ yahoo-group - don't forget to tell them you arrived via uhf-satcom.com ! There is another SDR-IQ info page from KL7UW here. Bjarne Mjelde has written up his first impressions of the SDR-IQ on his blog which can be accessed here