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Thanks to Dr. Dirk Baker
Antenna development at NIDR in the 1970s and 1980s – Some personal recollections.
This is from a presentation that Dirk did during a Technical Forum at CSIR DPSS on the 6th of May 2011.
A short story on Radar Warning Receivers back in the 1970s in preparing for the conventional threat.
By Denis Milton.
The Council for Scientific and Industrial Research (CSIR) was requested to design a Radar Warning Receiver (RWR) to help protect the South African Air Force (SAAF) aircraft from Soviet Union supplied surface to air missiles and fighters in the 1970s. This led to the RWR3 being designed with the following main parameters:
- Four channel (spiral receiving antennas) 500 MHz to 18 GHz, crystal detection receiver.
- To detect the Spoon Rest radar, two extra channels that worked in the 80 MHz and 150 to 170 MHz region were added to detect Spoon Rest A and B. Two large omni-directional antennas were fitted in the existing wooden section of the Canberra’s tail.
- The display had 8 lamps to indicate the direction of the radar detected. To reduce radar signals being heard on the intercom, each sector had a push button to disable the radar’s sounds from that sector.
- An audio recorder captured the necessary intelligence of all the intercepts.
All the known radars’ detection parameters were defined, and as test flights were conducted, the system proofed to work exceptionally well. The radar being used at Lusaka Airport in Zambia was however unknown. To detect and define the radar, permission was given (by the then Rhodesia) to fly to Kariba Dam, 150 km south of Lusaka. Unfortunately no radar from Lusaka was detected. The pilot then risked flying closer to Lusaka at 45 000 feet above the maximum height of Zambia’s Rapier missiles. Still no radar was detected, but the next day other intelligence sources reported that the radar was unserviceable and being repaired. The SAAF then used the opportunity to conduct some photo reconnaissance missions knowing that there was no search radar working and having the confidence that when it came on again, it would be detected.
The story does not end here. Television (TV) broadcasting started in South Africa in 1975. One evening on the TV news an interview with a politician at Lusaka Airport was broadcast. The familiar “buzz” of a search radar was heard interfering with the audio recorder. This sound was then recorded on an audio recorder when the news broadcast was later repeated. The audio signal was then analysed on a special computer that was being used to control a vibration test station. This computer was able to run an Fast Fourier Transform (FFT) that determined the Pulse Repetition Interval (PRI) and scan pattern of the radar. This enabled the make, model and manufacturer of the radar to be determined. The politician being interviewed never knew the secrets he was giving away that night.
RWR3’s electronic box and display as fitted to the Canberra
Thanks to Denis Milton
Started with RWR1 in 1975
This was a paper study of Radar Warning configurations and possibilities.
This was an Omni directional Radar Warning Receiver that covered 500 MHz to 18 GHz, crystal detection receiver. Lessons learnt:
- Need for direction information (angle of arrival).
- The linear video amplifier saturated. This would need more dynamic range if direction finding was to be implemented. This led to the development of the Log video Amplifier Detector.
This was a 4 channel (4 spiral receiving antennas) 500 MHz to 18 GHz. The display had 8 lamps to indicate the direction of the Radar detected. To reduce the signals being heard on the intercom, each of the 8 sectors had a push button switch that would disable the sound for radar threats from that sector. This meant that you could disable the sounds from the rear while flying towards the enemy. An audio recorder was used to enable intelligence gathering of all the intercepts. This would define:
- PW: The measured PW would be stretched by 100X to enable it to be recorded by an audio recorder.
- PRI: This could be measured by the time between pulses. PRI jitter and stager could be detected.
- AOA: The angle of arrival was coded into the right channel of the audio recorder by doubling the amplitude of the first pulse to enable scope triggering, and the sector that the signal was received was designated by doubling the pulse of the sector numbered from 1 to 8. Fortunately the search radars at that time would give more than the 9 pulses required to give this information.
Due the Spoon Rest Radar threats 2 extra channels were added to detect Spoon Rest A and B. These worked in the 80 MHz and 150 to 170 MHz region. Two large Omni-direction antennas were fitted in the “fortunately” wooden tail part of the Canberra aircraft.
RWR3 as fitted in the Canberra
Dennis Milton & Bob Collins before RWR3 Flight tests in the Canberra June 1976
ESD (Reutech) was then contracted to produce the Radar Warning Receivers for the Canberra’s.
Details on enemy Spoon Rest Radar
Spoon Rest Radar
- Frequency: 150 – 170 MHz (lower VHF-Band)
- Pulse repetition time (PRT) 2.77 milliseconds
- Pulse repetition frequency (PRF): 360 Hz
- Pulse width (PW): 6 microseconds
- Receive time: 2.4 milliseconds
- Dead time: 377 microseconds
- Peak power: 160 to 250 kilowatts
- Average power: up to 540 watts
- Displayed range: 200 nautical miles
- Range resolution: ½ nautical mile
- Beam width: 8 degrees
- Hits per scan: > 15
- Antenna rotation: 6 … 30 seconds (0 … 10 rpm.)
Chaff and Flare Dispensers
The CSIR started working on Chaff and Flare dispensers from about 1976. Keith Dowson and Mossie Basson were the main part of the team that developed the South African Chaff and Flare Dispensers. These were then produced by Grinel and this part of Grinel became Avitronics.
The CSIR designed and built voltage tunable magnetron jammers in about 1977. This worked in the X-Band. Bernard Bowers designed the control circuits. This was the first time that the SAAF pilots had the opportunity to see what the effects of Active Jamming were.
RF Synthesizer (leading to Frequency Hopping)
Denis Milton helped Derick Ashpole develop the Phase Locked Loop (PLL) used in the telemetry system used for missile testing. This technology was then adapted to enable Grinel to develop the Frequency Hopping Radios that have now become the “de facto” way of communicating in military systems to make listening-in more difficult. This was the start of EW in the communications field.
Upgrades to Radar and EW SAAF Equipment
Project Barber was used to improve SAAF EW and Radar Systems.
Radar Warning Systems
The Mirage F1 was fitted with AR91??? Radar Warning Systems that only gave 4 sector warning. To make it worse the front sector was for plus minus 45 Degrees. This made it difficult to know where the Radar was. This was modified to give out 8 sector warning. The front sector was now split to left and right. This meant that the pilot could easily detect the direction by doing slow turns and waiting for the signal to be shown from say left to right and then he would know that the Radar was directly in front.
Buccaneer Blue Parrot Radar
The Blue Parrot Radar was upgraded by Bernie Bowers. Bernie included a Pulse Width Discriminator to reduce jamming effects.