From: Dave Phillips (dphillips@ips.iac.honeywell.com) Message 1 in thread Subject: Re: Anyone work w/ RADAR ? Newsgroups: rec.radio.amateur.misc Date: 1995/12/19 View this article only Hugh It's been a few years, but I worked for several years as a Airborne Intercept Radar Systems specialist (Also known as "Fire Control") on the McDonnel F-4 C/D/E series of aircraft. This radar package was supplied by Westinghouse as the AN/APQ100 (F-4C), AN/APQ109 (F-4D) and the AN/APQ120 (F-4E). The functional characteristics of this system included two transmitters. One was a variable pulse rate search/track system, the other was a CW illumination transmitter (1KW) used to provide illumination and tracking range/rate (via doppler) for the AIM-7 E/F Sparrow Missle. The main system components are housed in a package that conforms to the aircraft nose section forward of the cockpit, and slides out on a rail for servicing once the radome has been opened and swung aside on its hinge. The only components housed in the cockpit area are the control boxes, display generator and the scopes. A conventional weapons delivery computer and a gyro stabilized lead computing gunsight components were stored in a bay behind the cockpit (F-4D/E only). Although the computers used were Analog not Digital, this radar system provided very accurate airborne search and ground mapping capabilities, and in the late 1960's was the state of the art in airborne systems. The primary function of the pulse radar was search and track. This was performed by generating a variable frequency and rate pulsed transmission (variable is much harder to jam) which was radiated by a rotating feed horn on the antenna. The antenna has a sweep of 120 degrees azimuth and 85 degrees in elevation. The feed horn rotatation is eliptical ("nutated") in order to provide a wider dispersion of the radiated signal when illuminating small fighter size targets at max range when aquiring and locking on to a target. Effective search range of this radar is approximately 100 miles, and accurate airborne track is approximately 30 miles. The system also aquired information from other aircraft systems (primarily the Air Data Computer and Inertial Nav systems) to determine the alititude, speed, course and attitude of the host aircraft. This information was in turn used to calculate the optimum range and steering information for weapons such as the Sparrow, as well as a number of semi-smart conventional air/mud weapons. When I worked on the systems at the USAF Weapons Center at Nellis, the radar system was integrated to provide aiming and target tracking information for the Wallye glide bomb and the AGM-45 Shrike anti-radar strike weapons. Later, it was also integrated with the first laser designator system. In both cases, the radar displays were used a television displays showing true target image. Basicaly, a pulse from the transmitter travels through free space at approximately 1 mile every 6.3 microseconds. This is close to the speed of light, and is the same basic velocity used for all radio wave propogation calculations. A pulse that travels a distance of one mile, strikes a target and is reflected back, is recieved back at the transmitting site 12.6 microseconds after it was transmitted. This time increment is known as the standard "radar mile" and governs the design of all radar tracking systems. For example, most wide area sweep radars which are designed to provide 100 mile coverage have a rotation period of their antenna set to 12.6 seconds. In a fighter aircraft like the F-4, the primary reason for having the radar on board is search/track/attack of airborne and ground targets. Navigation and weather observation are a secondary use. The radar reciever utilized a range gate tracking technique to determine provide range information. When a target was illuminated, the weapons control pilot in the rear cockpit could move a range gate aquisition strobe over the target and "lock on". This set the tracking range gate which would provide steering and range information for the target. A synchronizer computer (Analog) would then command the radar antenna to track the target. Once locked on, the CW illuminating radar was turned on to provide a continuous beam which would be "ridden" by the sparrow missile. The missle used two antennas, one forward and one aft, which prior to launch were fed with the target reflected doppler shifted signal (forward) and the transmitted signal (aft). The missile contained a klystron tuned oscillator which tuned automaticaly to keep these two signals in reference. The difference of these two reference signals represented range to target. When launched, the missile followed the beam by keeping the fwd/aft antenna aligned by measuring signal strength in flight and adjusting to keep the beam centered. As the missile closed on the target, the aft antenna would sense a increase in the reflected signal frequency due to doppler shift, and the aft antenna would sense a decrease. When the difference between these two frequencies reversed, the missile was "at target" and the wardhead (28 feet of folded beryllium rod wrapped around 64 pounds of high explosive) was detonated. Nasty little beast. Should the illumination signal be lost while the missile was in flight, the on-board klystron would continue to slew at the last known rate and act as if the signal was still being recieved. Known as a "home on jam" feature, this allowed the missile to remain committed. Since it flew at Mach 3.5 plus, it was very difficult to jam and dodge this missile. Unfortunately, it was designed to intercept bombers at ranges in excess of 15 miles and was not very useful in a fighter versus fighter engagement where ranges tend to be less than 2 miles. Since the missile can not maneuver while its rocket motor is burning (3.5 seconds), this close range would often result in the missile going "balistic". This radar system is a simple one target at a time tracking/attack system. More modern system today use pulse doppler and digitaly scanned antennas and can track multiple targets, but the basic priciples are still the same. This little brain dump should get you started. I had forgotten how much I knew about this beast until I started typing. Hopefully, I haven't bored you to tears. Happy Hollidays Dave Phillips From: Tom Randolph (randolph@est.enet.dec.com) Message 2 in thread Subject: Re: Anyone work w/ RADAR ? Newsgroups: rec.radio.amateur.misc Date: 1995/12/22 View this article only In article <4b7j3f$dhr@cst715.iac.honeywell.com>, Dave Phillips writes... >This little brain dump should get you started. I had forgotten how much >I knew about this beast until I started typing. Hopefully, I haven't >bored you to tears. On the contrary, very interesting. It's neat to hear the details of this stuff, which I've only had a vague knowledge of for years. You know, "rides a radar beam". That's about as technical as most books get. ============================================================================== Tom Randolph N1OOQ NE-QRP 419 QRP-L 87 ARRL randolph@est.enet.dec.com ==============================================================================