The photos of this meeting are [here]
At 14h00 on Saturday 24 June 2017, the CTARC held its monthly meeting, following on from the New Hams lecture delivered at 13h00 by Rob / ZS1SA. In general, your committee tries its best to arrange for interesting speakers and topics at the monthly meetings, but the 14h00 talk (presented by Stephen Paine and Skippy Burger / ZS1SKP) raised the standard of excellence to a new level. We all sat riveted to our seats from start to finish!.
Rob opened the meeting with a report back from the recent committee meeting. The recent storm damage to our HF antennas was discussed. The club is purchasing a set of RF Band-Pass filters for use at the Lighthouse Weekend coming up in August. John / ZS1AGH was thanked for providing the embroidered CTARC cap for Gerban /P5GM who gave the May 2017 talk on DIY DX-peditions. The radios for the Lighthouse Weekend, suitably repaired, have been returned to the club. The forthcoming July AGM was mentioned (soup & sherry in the pipeline!)(served separately) and the forthcoming September and October meetings referred to as well.
Then Rob introduced Stephen Paine, a UCT postgraduate student who is working towards his PhD thesis at the Radar Remote Sensing Group at UCT. Stephen started with a brief resume of the RRSG, which has been empowering scientists and engineers in the challenging fields of Radar and Electronic Defence since 1988. As such it has strong links with the CSIR and appropriate industries.
We were then given a brief introduction to what Radar actually is, and what its applications are. In addition to the traditional roles of target detection and range, height, angle and velocity measurements, radar is also used in Guidance Systems, for weather- and environmental monitoring and for Imaging. The need for radar was vividly illustrated when Stephen illustrated to us just how populated with aircraft international airspace has become.
We were then gently led into the basic of radar technology, the calculation of distance, the resolution of radar systems on different frequencies, the block diagram of a basic active radar system, radar cross sections for reflecting energy back from the target, the basics of Doppler systems and concepts such as such as the radar horizon, radar clutter and shadowing. Stephen then showed us the basics of radar direction-finding using phase-difference measurements to determine the Angle-of-Arrival of reflected radio waves.
Then things got really interesting. We were introduced to current Radar projects underway:
- NeXtRAD, a current project using a netted, dual-band, dual-polarisation radar system, is used to detect small vessels in rough seas. You can imagine how useful this would be for detecting small craft in distress and marine poachers;
- DroneSAR, a portable Synthetic Aperture Radar system is used for agricultural crop monitoring and seedling growth stages – vital in the context of the developing food security issues in Africa;
- ComSense is a low-cost GSM receiver system for environmental monitoring using GSM signals.
At this point, Skippy / ZS1SKP was introduced. He’s also a PhD student at the RRSG and his section of the talk was on a current project in his field in HF (3 – 30 MHz) radar, specifically for Over-The-Horizon coastal surveillance. There’s a two-fold need for that:
- Oceanographers and SA Weather Services are interested in ocean current data. The behaviour of the Agulhas Current off the South African coastline has significant implications for climate change;
- The South African Navy has a particular interest in monitoring (and protecting) the 200 nm Exclusive Economic Zone off our coastline.
Skippy showed us the basics of an HF Surface Wave Radar system, consisting of several monostatic element nodes, each controlled and synchronised by Ethernet. At least three nodes are required to get meaningful results. By using seven distinct nodes, greater angular discernment of the return signals is obtained.
Each node’s HF Digital back-end (the “Red Pitaya”), which was developed at the RSSG, consists of an ARM processor, Xilinx Zynq 7010 Field Programmable Gate Array, two Analogue-to-Digital Converters and two Digital-to-Analogue Converters, each running at 14-bit resolution and 125 Msps. The Ethernet controller runs at 100 Mbps.
Each antenna is a 4-wire biconic design centred on approx. 21 MHz with a bandwidth of 14 MHz and a gain of 4.5 dBi over full bandwidth. The one drawback of HF radar systems is that they require real estate along the coast for the HF antennas, which need to be spaced out. Any sympathetic radio ham out there with about 100 metres of real estate along the coastline? Skippy is looking for a site to do some (temporary) beta testing.
The presentation then switched back to Stephen who spoke about their current project, which is the development of a Passive Radar system. Here, the radar transmitter is a local broadcasting station on VHF-FM. By using a Bi-static system ( consisting of a Reference Antenna that picks up the Line-of-Sight signal directly from the BC transmitting antenna, and a second Surveillance Antenna that picks up the target’s reflected echo signal) aircraft positions can be tracked over time. We were shown a complete Passive Radar Receiver, using (highly desireable) Ettus USRP N210 SDR receivers at the core via and lots of low-pass filtering to remove clutter and Low Noise Amplifiers to recover a pure signal. Using antennas mounted on the units building at UCT, with a broad view over the Cape Flats and DuToits Kloof Mountains, aircraft can be detected and their position tracked for around 200 km. At Passive Radar tests done at the Square Kilometre Array site, tracking ranges of up to 700 km were achieved (something of a world record) in that radio-quiet environment.
Stephen and Skippy then fielded numerous questions from the audience, with a relaxed style of those who are particularly well-informed in their field. It is highly gratifying to note that South Africa and UCT still continues to produce individuals of such intelligence and calibre.
Afterward the lecture (two hours had passed with us hardly noticing the passage of time) there was the usual pleasant post-meeting bunfight that consists of coffee, biscuits, eyeball QSO’s and horse-trading in various swops brought along to the meeting. Definitely one of our better lectures! Photos [here].
Next month (22 July 2017) will be the CTARC Annual General Meeting, an event not to be missed. See you there!