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You're welcome - although, in retrospect, I incorrectly corrected my first post! (are you confused yet, because I am ) The numbering system for the WRA's/LRU's (same thing) was just a little bit confusing, because on the port side of the radar, the numbers increased from forward to aft, (eg: antenna=LRU 1, then LRU 4 was the entire pallet (but never removed as an entire unit), LRU 5 (never entirely removed as such) and LRU 6. Then, on the 4 pallet, 4A1 was the topmost 3rd, 4A2 was the center unit, and the 4A3 was on the bottom. You can see on the 4A1 and 4A3 units what looks like ribs, those are actually removeable "boards", sort of the shape of a watermelon slice. They're held in place by one (slotted and hex-head) captured screws, one on top and one at the bottom.
On the starboard side, the LRU 2A1 was the transmitter control box, on the top of the package. It was long and relatively thin, shaped rather like a piece of wall to floor molding, only thicker (and aluminum) Below that was "the hat" - a large aluminum cover that was held on with what seemed like a zillion #8 Phillips-head screws. This "hat" was the cover for the pressurized (air, to 14 lbs/in2) transmitter power supply compartment.
There were two separate power supplies, one for the CW illuminator KPA, and one for the main KPA. I believe the LRU 2A2 CW supply put out 22,000 volts, and the main 2A3 supply put out 25,000 volts - at high power. Those supplies were about the size of a loaf of bread each, but were VERY heavy. There were high-power rectifier tubes in those supplies that had large cooling fins on the bottom - as a matter of fact, they made very cool ashtrays when the tubes went bad (I had one for many years, and the wife threw it out!! Arrrgh!)
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Could you comment more on that radar, per example:
a) How many radar modes did the RIO has for air combat (BVR and ACM) and how were the scan patterns in azimut and elevation (bars).
There were six "bars" that I remember. I don't recall the starting bar, but if the bars were numbered as such:
1
2
3
4
5
6
I believe the vertical scan pattern went something like: 2,4,1,5,6,3
It wasn't quite what one would expect. I don't recall it changing the bar scan pattern - but remember, the last time I worked on those things was 27 years ago.
As far as modes - they could select PULSE, PD (both ACM modes) A/G (which was the ground mapping feature, 120º PPI (Plan Position Indicator) mode) and I believe T/C or TERRAIN - this last very obscure feature was very difficult for aircrew to understand; it was supposed to indicate to them the likelyhood of collision with terrain features when proceeding at high speed, low altitudes (eg:bombing runs). The antenna scan pattern was that of a "+" - Full Up, Full Down, Center, Full Port, Full Starboard, Center (repeat) The scan displays on both scopes was also a "+". However, a number of crashes occurred while using this mode, and it's use was discouraged by modifying a card in the LRU-10 (Cockpit Display Unit, aft cockpit, port side, just under the canopy rail) to display a large "X" on the screen. As mentioned above, the pilot could select DOGFIGHT mode, which would override the RIO's controls, select short pulse, 10 mile range, and enable VTAS acquisition by sweeping out the range gate upon the pilot's pressing the lower button on his joystick.
The RIO had his own joystick, mounted to the right of the scope and above it. The RIO's stick was about the size of a screwdriver handle, or straight sausage-shaped on a ball mount. It had an "action" button under the middle finger, and a thumbwheel on the top. The thumbwheel controlled the antenna's elevation. The elevation was indicated on the scope as a short horizontal blip on the right side of the screen. Pressing the button halfway down was called "half-action", this would cause the antenna to be slaved to the RIO's stick, and would initiate 60ms PRF switching to prevent target eclipsing.
There was also the "taboo" mode, "EMERGENCY". This mode was to be used ONLY if you were in actual combat, and you had a transmitter failure. This mode overrode all of the thermal sensors, and a number of other protection circuits. Selecting this mode might enable the transmitter to work for a short period of time, but at the likely cost of destroying a number of radar components. When a RIO selected this mode, it tripped a red flag on the knob, which could only be re-set by removing the knob with a small Allen-type wrench. That was one of the very first things we would check after a flight - if that flag was out, the RIO got a trip up to the Skipper's office for an ass-chewing.
There may be more modes that I've forgotten. The last couple of years I was on active duty, we got F-4S's with the AWG-10A's in them, then I transferred to VMFA-122 which had the older F-4J's with AWG-10's again. One can't remember everything from 27 years ago
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b) You commented that the PD mode was the most difficult to use and based on velocity closure (range rate) and not in range vs azimut. That means something like "VS" mode on AN/APG-68 I mean, that's a HPRF mode isn't?. Do you remind any interesting peculiarity of those modes, per example how did they worked according to different clutter environments and target profile?, was that mode only LD or it was also available as a Look up option?
PRF was approximately 40ms in PD mode; but remember there still was minute adjustments made to the PRF at the end of every scan, and it would switch every 60ms during half-action or acquisition.
One interesting aspect of the PD mode was the ground clutter notch. This looked rather like an inverted arch. The faster the aircraft was travelling, the taller and narrower the arch was. It was, literally, a "black hole" - the radar would not "see" anything in that notch. It would take digital signal processing to make use of that ground clutter return, which wasn't until later. Remember, the electronics in the AWG-10 were quite crude by today's standards - their idea of an integrated circut back then was a collection of discrete components surrounded by a black cube of epoxy. This is also what made it so difficult to repair, and gave it a low MTBF.
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c) Can you comment on the MTBF of the radar set, compared to other radars on Phantom and vintage aircraft you know?, it introduced LRU philosophy?, how it was to mantain?, would be delighted (and guess most of us) to hear more about your job
The MTBF on the original AWG-10 radars we had was quite dismal; if an aircraft was still "up and up" (airframes/radar) for three "hops" (sorties) it was golden. Remember, these aircraft were doggone old by the time I got to operational squadrons back in 1975; they were all Vietnam Veterans, and had seen MANY launches/recoveries from aircraft carriers, and were very high-time airframes. A single F-4J Phantom had 15 miles of wire in it. That's a lot of wiring to maintain. Much of it involved the radar. And the radar had quite a few electro-mechanical relays. One of our most frustrating "gripes" would be, "Radar breaks lock under G's" to which we could only reply "G-force simulator on back order." They wouldn't let technicians fly in the backseat - so we couldn't begin to troubleshoot it.
The BIT box (LRU-8) was a troublesome piece of equipment (BIT=Built-In Test) - it was driven by a film strip with written instructions and frame numbers to tell you where it was in the test, and a grid of (logical) 1's or 0's (either black or see-through) that drove a series of either phototransistors or photoresistors, which controlled a "relay tree" above the antenna that would select various circuits to test. This thing was a nightmare in itself. The AWG-10A BIT box was infinitely better; it was all digital, and markedly faster.
When my 1st squadron got the very first F-4S's with the AWG-10A radars in them, we found them to be VERY reliable in comparison - we were getting 10, 20, 30 or more hops between repairs. However, the first time we went to swap out a computer (LRU15 or LRU16, can't remember which) in the turtleback (behind the RIO) we discovered that the computer harness had been made too short! We got the cables off OK, but they just wouldn't go back on the new computer. They'd made an error in measuring the "jig" used to build the cables.
The F-4S's had other teething problems. They changed from the old flammable hydraulic fluid to a new, non-flammable hydraulic fluid; however the old O-ring seals were not compatible with this new fluid. Well, they supposedly replaced all of the O-rings when the airframes were rebuilt, but they missed a few in the turtleback area, causing eventual massive hydraulic leaks and our squadron to nearly lose an aircraft after losing all hydraulic pressure during approach.
d) Did the radar interfaced with advanced con scan Sparrow (AIM-7F) and monopulse Sparrow (AIM-7M) missiles?...
I left the Corps before those missiles were available. The Sparrow missiles I worked with connected to the missile umbilical using a 32-pin shear "wafer". When the missile was ejected from the rack (by firing what amounts to a blank shotgun-shell type device) the wafer would actually shear in half; one side would remain attached to the missle, the other half would stay with the harness. I have a couple of these "wafers" left from my tour in the Corps; I was using them to build Sparrow missile simulators so the aircrew could practice locking on the radar and firing when the missile was inside the envelope. Don't have any photos - yet. They're rather crude, we didn't have any circuit card material available - just soldered together a dozen resistors, capacitors and diodes along with a fuse holder, then potted the whole thing.
Thanks a lot for any answer and for the last post.
You're welcome - hope this is enough for the moment. It's after midnight here, it's been an event-filled day, and I have more to accomplish before hitting the rack.
More to come...
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