The carrier based aircraft operating near Vietnam was supposed to turn a manual switch on their Radar Warning Receiver (RWR) to short out the receiver before they left the plane. They were also not supposed to activate any of their radar's while on deck. If both of these rules were broken the result would be that the RWR with the switch in the receive position would have it's front end burned out. The pilot would not know this until he was attacked with no warning from the RWR.
The soviet block surface to air weapons were the SA-x missiles and the ZU-23 gun.
At the time I was working at Aertech Microwave and we had just
started to make microwave modules. These were patterned after the
HP comb
generator and PIN diode switch modules that were cylinders about 1/4"
in
diameter with glass to metal seals in each end. The HP design
sealed
the outer sleeve to the module using a welding process that left the
end
rough.
This unit had a metal strap forming just under 1 turn that induced
current
in the sleeve and module bringing them to solder meting temperature
within
seconds. To get a good joint HP had a recess that was the
mating
surface for microwave contact. This was a difficult thing to make
without adding an extra part and so was more expensive than our way of
doing it.
I designed our module so that the mating surface was proud of the
rest of the module on each end and used a solder process to seal the
module.
Rather than use an iron to solder we used a Seven Associates single turn
inductive
heater
with the module held in vertical position so you could see the end
under
a microscope. A solder pre form was placed in the groove designed for
this
purpose and the heater start button pressed. In a few seconds the
solder
sealed the module. The module would then be leak tested using
Helium. Helium is the smallest molecule available for leak
testing, Hydrogen is a diatomic gas and has a module that's almost
twice as big as Helium. Helium leaks out of balloons much easier than
hydrogen, that's why mylar helium balloons stay aloft much longer than
rubber ones.
Rucker
& Kolls and Micromanulipator were the common analytical probe
stations that we used a lot. These have a level horseshoe ring
that moves up and down relative to the chuck. A stereo zoom
microscope and an illuminator would complete the station, plus the
probes and test equipment. The micrometer head sets the down
height of the horseshoe. The black knobs on either side raise or
lower the horseshoe. You can see a double sided socket for a
plug-in PCB below the horseshoe and there were (are?) companies that
would make up probe cards with the tips where you wanted them so you
could use either a plug-in card or individual probes mounted on
magnetic mounts, each with it's own positioner. The knurled knobs
in the front are the X-Y stage adjustments. The black knob at the
very front is for stage rotation.
We had a number of different modules in our product line including switches, comb generators, limiters and detectors. A need came up for a combined limiter detector for a classified military program related to Vietnam. This was for a Quick Reaction Contract (QRC). These contracts typically carried a government priority rating of DX-A7. This meant that we could get our orders delivered before any civilian got his parts and it also meant that the program was watched very closely.
The common RWR at this time was called a "Crystal Video" microwave receiver because it had no RF amplification ahead of the detector and no mixers or Local Oscillators. An early patent for a Microwave Filter and Detector filed in 1958 and granted 1960 is US 2954468. You can see that the "filter" grew into a multi band device.
This Detector (no
limiter) has a meandered ceramic matching section. I made up a special
housing to hold our separate limiter and detector (LD) in a long
tube. On one end was the microwave input SMA(m) connector and on
the other end was the connector for the detector output.
I took this prototype up to the Applied Technology Inc. building on a hill in the Stanford Industrial Park. It had a great view of the Palo Alto bay area. Inside there was a room with walls formed by chain link fencing that went all the way to the ceiling. The gate was open and there were men inside carrying snub nose 38 revolvers.
We tested the prototype by applying radar level power levels (accounting for the path loss across a carrier deck) then checked to see of the detector was fried. It passed.
Limiter-Detecton
in a single package. I bent the leads
to get the module to stay upside down on the scanner. The two
black dots to the left are the shunt limiter diodes, then a 1/4
wave ceramic transformer with a Schottky diode mounted at the right
end,
then a ceramic capacitor. I next designed a way to package a
combined
LD in a single longer module and add a housing at the back to hold the
factory select bias resistor and blocking capacitor, DC bias terminal
and Video output terminal and have the mounting holes and RF connector
be in the same place as the original detector. This was a form,
fit and function replacement that included both Limiter and Detector
functions..
This is a
reject unit without the rear (right end) cover installed. The
back end housing was made from a piece of square Aluminum stock with
a single round cavity (easy to make with a milling machine or screw
machine). The printed circuit board (PCB) that went into the housing
was circular
in shape with a diameter that matched a punch that was already in our
machine shop. The PCB could be made up in advance with a range of
the common resistor values used for setting the detector bias and once
the operators had determined the correct bias the correct box would be
mated to the limiter detector.
The ALR-xx systems that used these LDs covered a very wide frequency range. This was handled by using a triplexer (or quadraplexer) to split the input frequency band into narrower bands. The exact frequencies were classified. We built the LDs in various bands to match the requirements for each system.
Another version
was the Switched Limiter Detector where the limiter DC return was
brought out on a connector. That way you could apply a
bias to the limiter diodes turning them on as PIN switches. This
allows the detection of a CW signal. This is a prototype
unit. An earlier version applied the limiter diode bias from the
back end of the module, but that did not work because there was cross
talk between the diode drive signal and the detector output.
The modules were tuned in a clean room using various test setups. Early on we used the Systron Donner small sweep oscillator that had a box full of signal generator heads and switched between them to get a wide band sweep. The setup included either an HP Scalar Network Analyzer (SNA) or shortly later the 8410 Vector Network Analyzer (VNA). There were some simple things that could be done to determine how to improve the VSWR by the use of the VNA that were not possible with the SNA.
A good VSWR that ws obtained by good matching was far superior to a good VSWR that was obtained by loss. This made our LDs more sensitive and at the same time they had the limiter to protect from carrier zapping.
This project is documented in a movie produced by the Association of Old Crows called "First In, Last Out" that chronicles the early days of the Wild Weasel program.
Test Equipment
Sweep Generators
In the beginning Aertech used Alford BWO sweep generators, these literally could be used for boat anchors. Later the HP 690 series sweepers with the plug-in BWO and snap in plastic frequency dial were used. It was possible to put a number (3?) of plug-ins in one rack and the master in another in order to sweep more than one standard band (standard bands were AFAICR, L = 1 to 2, S = 2 to 4, C = 4 to 8, X = 8 to 12.4, K = 12.4 to 18, Ku = 18 to 26 GHz). Then the Kruse Stork 5000 solid state sweeper and it too had a combiner for multiband sweeps. Then the HP 8350 sweepers came out with a single plug-in for multi-band sweeps. These had poor phase noise, but for most microwave components work worked well. You could tie two together for mixer work. Then there were the synthesized sweep generators with excellent phase noise that were required for precision mixer work.HP 415E SWR Meter
This is really a very narrow band AC voltmeter centered on 1 kHz. Maybe a few Hz bandwidth. When working with weak microwave signals you can 100% AM modulate the RF (either using the internal 1 kHz modulation feature of the sig gen or an external PIN diode modulator) then feed the output from a detector to the 415 meter. Originally these were used for making slotted line VSWR measurements, but can be used for other applications.HP 3400 True RMS AC Voltmeter
This is the only meter that I was aware of that could make such a wide band true RMS measurement. Used for making noise measurements in a number of applications.Also see my Microwave Test Equipment and Military Test Equipment pages.
