Radar Warning Receivers

Background and General Information

The Secret History of Silicon Valley (56 minutes) Google Tech Talks, Dec 18 2007 by  Steve Blank is a very interesting overview of Electronic Warfare and how Stanford professor Terman helped develop the west coast infrastructure.  Highly recommended.  The cost in human lives is has a noticable impact on Steve.
Hidden in Plain Sight (1:02:45) at the Computer Museum,   by Steve Blank, Nov 20, 2008  - a very similar talk

The PDF version is as it appeared originally and contains all the illustrations, some of which may be missing or distorted in the html version.
Moon Bounce Elint - PDF - a  CIA paper was SECRET NO FOREIGN,  declassified 2 July 96 - why the Stanford 150 foot dish is one of the best for Moon Bounce ELINT
QUALITY ELINT - PDF - a Feb 1968 CIA paper was SECRET NO FOREIGN,  declassified 2 July 96 - looking at antenna patterns along with actual power levels.
An Elint Vigil, Unmanned - PDF - a  CIA paper was SECRET NO FOREIGN,  declassified 2 July 96 - about the SA-2 SAM system (one of the systems the Limiter Detector was developed) a proposed automatic system (was it deployed?).
Communist Defense Against Aerial Surveillance in Southeast Asia - a  CIA paper was SECRET NO FOREIGN,  declassified 2 July 96 - all illistrations at end of paper
THE OXCART STORY - a  CIA paper was SECRET,  declassified 2 July 96 - about the A-12, aka SR-71
SCIENTIFIC AND TECHNICAL INTELLIGENCE ANALYSIS - a  CIA paper was SECRET,  declassified 2 July 96 - includes mention of SA-2 & SA-6
ELINT a Scientific Intelligence System - PDF - 12 page overview formerly SECRET declassified 22 SEPT 93
The U.S. Hunt for Axis Agent Radios - PDF - Official Use Only declassified 18 SEPT 95 -


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.

AN/APR-25

1966 vector receiver (the small CRT showed the relative bearing to the threat as the angle from center screen, and the distance from center screen was a relative distance to the threat, made by Itek used to detect:

• S-band emissions from SA-2s
• early warning ground-control radars
• C-band radiations from the  improved SA-2 radars
• X-band characteristics of airborne intercept radars

S/X/C-Band Radar Detection and Homing Set; manufactured by Itek; part of AN/ALQ-27; used in A-7E, U-8, U-21, OV-1D, B-52G, RA-5C, A-6E, F-4, F-14, F-100, F-105, C-123, C-130
eBay photo of APR-25 cockpit display - Another CRT photo 

AN/APR-26

crystal video Radar Warning Receiver made by Itek  Used to sense power-level changes in the L-band command guidance radars of the SAM i.e. a launch detector.
SAM launch warning system
SAM Launch Warning Set; manufactured by Itek; used with AN/APR-25; used in F-100, F-4, U-8, U-21

AN/APR-36

Homing and Warning ECM Receiver (improved AN/APR-25); manufactured by Itek; used in F-105, EF-4E, A-7, B-52, F-5E/F
IP-957/APR-36 - CRT display showing relative bearing to and type of threat by Applied Technology Inc (ATI) another view - Label -

ECM Signal
Can anyone define for me what the "BG06" SAM signal was and how the EWs "played" with it?  I'm a retired Lt. Col. who flew Ds as a Nav on CAR E-57 during LB II from Andersen.  B...  B,,,,,,

Re: ECM Signal
BG06 referred to the guidance channel for the SA-2 missile. The missile was tracked by the targeting radar and corrections to the missile were up linked to the missile via the BG06.

Since the BG06 antenna was "looking" back at the launch site, the only way to jam it was to be between the missile and the site. To do this, either you were below the missile doing support jamming or you were lucky and the missile missed you.

The radar warning receiver had a launch light to indicate the BG06 was active. My experience was that the light was inaccurate. I looked for the signal on my ECM receiver.

I an unaware of any way to play with it.

Joe

AN/APR-38

Radar Homing And Warning System; used in F-4G; replaced by AN/APR-47

AN/APR-39

TM11-5841-283-12 Operation & Maint Manual is on line at ETM as PIN 053495.pdf
IP-1150 CRT eBay photo

AGM-45 Shrike Missile

Made by Texas Instruments.  There were a number of different seeker heads that could be installed, each for a different target.
We made a set of 4 matched detectors for one of these heads.  The one shown is band IX.  After properly torquing the SMA nut on the RF (bottom) end a tube with a flange was slide down and the O-ring seated on the tube.  The flange was bolted to the guidance section to support the detector in the high vibration environment found on an aircraft wing.  A computerized test system was used to measure hundreds of detectors at a time and output the serial numbers of the matched sets.  We could match much better than the spec using this system and it improved our yield.  (Another version of this test method was later used by ST Microwave to match detectors fro a satellite program to extremely tight tolerances.)

Since the frequency band was determined by which guidance section was installed on the missile, the target needed to be known before take off.

The Shrike has the steering wings located at the center of mass of the missile.  This causes the missile to move sideways rather than to rotate.

AGM-88 High-Speed Anti-Radiation Missile (HARM)

Made by Texas Instruments.  This is the system where we used the HP 8566B spectrum analyzer to directly measure the spurious mixer products very quickly.  This system was in an access controlled room and had a number of security features.  The test time was reduced dramatically compared to manual testing.  The HARM could be tuned to any desired frequency so one missile could be used for whatever target came up.

AN/ALR-45

2-18 GHz Radar Warning Receiver; manufactured by Litton; used in F-8, F-14, A-4, RA-5C, A-6, EA-6B, A-7, F-100, F-4, F/A-18, CF-104 (Canada)

I think this is the one that we made all the LDs for?
Control - Close Up - Label - 3 buttons for enabling or bypassing the lo, med and high frequency bands, also 3 buttons for Built-In-Test of the three bands and these double as AAA, AAA/AI or AI selectors?

AN/ALR-46

Digital Warning Receiver; manufactured by Litton; used in B-52H, A-7D, A-10, C-130, F-104, F-105G, F-111, F-4, F-5E/F, RU-21H, OV-1, OV-10, HH-53

AN/ALR-53

long-range homing receiver

AN/ALR-54 LAMPS

ALR-62

Used on the F-111
Antenna: AS-2943/ALR-62

AN/ALR-73

0.5-18 GHz Multiband ECM Receiver (improved AN/ALR-59); manufactured by Litton; used in E-2C

AN/ALR-100

(also called the LR-100), a lightweight radar signal receiver designed in-house by Litton Amecom using COTS (commercial-off-the-shelf) components. It can serve as a radar warning receiver (RWR) and also provides precision emitter location and identification (ESM/ELINT) as an electronic support measurers (ESM) system.

AN/AAR-60 MILDS (Missile Launch Detection System)

Polar Frequency Discriminators =  Instantaneous Frequency Measuring

This microwave component is composed of a combination of power spliters and couplers and contains 4 detectors.  One pair of detectors provides either an X value and the other pair provides a Y value for a vector.  The magnitude of the vector is proportional to the amplitude of the incoming signal and the phase angle is proportional to the frequency of the input signal.  In order to get higher frequency resolution you can combine a number of these using delay lines that are increasingly longer so that the frequency is read using a gas meter approach.  In this way you can make an instantaneous frequency measuring (IFM) receiver.  Note that this receiver can determine the frequency of an incoming signal on only one pulse.   We made a number of different models of this device.
Wide Bnad Systems - makes these
WJ App Note: High Probability of Intercept Receivers in an EW Environment -

W.W. II Glide Bomb

Aertech

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