UHF-Satcom.com - A brief review of the RF-Space SDR-IP software defined radio                                                (04/03/2010 12:42)

UHF-Satcom.com received one of the first SDR-IP ‘test’ units from RF-Space. One of the main features of the SDR-IP is that it can sample 2MHz of RF in real-time, and transmit the I/Q data out over 100mbps Ethernet. This has some great applications, such as the demodulation of wide-band data modes, as well as recording large chunks of RF for later play back and analysis. The SDR-IP ADC clock runs at 80MHz, with the option of locking this clock to an external 10MHz source, such as GPS or Rubidium. The SDR-IP also has an RF output which is driven by a 200MHz ADC. This means that its possible to use this output for generating test signals, playing back recorded RF, or digitally passing through the incoming RF signal. When used as a test signal, ‘white noise’ can be generated over a 40MHz span, allowing for example, the internal filter banks to be checked. The SDR-IP is housed in a decant metal case, not only providing good RF sheilding to CE/FCC standards, but also providing good physical strength. The digital radio operates off a 5V supply, and needs around 1.3A.

(above) SDR-IP showing the display when used with external radio – in this case it is connected to an AOR AR5000+3 communications receiver.

(above) SDR-IP showing the rear panel with associated connectors. The Aux input is for the optional internal down converter board, whilst the trigger input allows for multiple SDR-IP's to be locked together. The Serial port allows connection of external receivers such that the tuning or mode selection can be synchronised between SpectraVue software and the receiver.

(above) Network utilisation when running in 2MHz mode shows the incoming data rate as 66.87Mbps. Gigabit Ethernet is used to allow sufficient network overhead for other tasks.

Initially, the SDR-IP can be configured from the front panel, using the menu and select controls, which are push able rotary encoders. These are used to set various configuration items, such as TCP/IP address, netmask, default gateway, and IP port number. Other options allow DHCP configuration of IP address, and selection of FPGA firmware.

The on-air performance was checked at HF, and also as an IF processor for an external receiver. The HF performance is extremely good, and shows that not only does the receiver have a high dynamic range, quoted as being greater than 105dB, but it is also very low noise. When tuning across the HF bands, one of 10 band pass filters can be automatically or manually selected. The filters have extremely low ripple. An example is shown below of the 10MHz to 14MHz band pass filter, using the built-in noise generator. As can be seen, the response is flat between the relevant frequencies.

(above) Internal band pass filter checks using the built-in noise source.

It should also be noted that using the noise generator and 'real mode' would allow filters etc to be tuned or adjusted in real time, providing they are operating in the frequency range 0 to 34MHz.

One of the first uses of the SDR-IP at uhf-satcom.com was to record the Space-Shuttle S-Band downlink for further processing. The downlink is centred on 2217.5MHz and is BPSK running at 1.152Mbps. This was an easy task using the SDR-IP, and following the recording of the signals, it was possible to demodulate, de-frame, and recover the air to ground channels one and two. The screenshot below shows the downlink during playback;

(above) STS-130 S-Band BPSK downlink. Results of the sound decodes are available on the sounds page.

In the S-Band BPSK FFT picture, it is possible to see the antenna switching point, around 1/2 way down the waterfall. This is when the Shuttle switches to another antenna in order to provide the best possible signal to the TDRSS satellites.

More to come!

If you are interested in seeing what other users think of this SDR, its well worth joining the SDR-IP yahoo-group - don't forget to tell them you arrived via uhf-satcom.com !