I'm... I'm a Monster!

Zelja said:

It's alchemy!! Get a chance to measure the DC resistances of the 2 coils?

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I have not. Traveling at the moment.

GAD said:

I used to work with telephony engineers and they used to mess with newbs by telling them it worked via HPFM. And that if HPFM wasn't running it wouldn't work.

Hocus Pocus F-ing Magic.

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I used to work in a place run by a couple of engineers who specialized in microwave circuits and antennae for EW/ECM* applications.
Export-controlled stuff, the company tested microwave components and shipped over the stuff that passed, to an Italian outfit that built modules for use in Italian NATO ASW** helicopters in late '70's.
I'll never forget the time the guy who did most of the testing tried to explain VSWR to me.
While he was bitching that the coax cable between component and transmitter was picking up radar signals from Moffat Field a couple of miles away that were showing up on his 'scope and he just couldn't filter 'em out.
It was of course at a frequency for which only the US military had access to components capable of filtering or jamming the signals.
But lower harmonics of the signal were distorting the wave forms in the 'scope display making it almost impossible to accurately measure the SWR at different frequencies and current.
These days that stuff is probably all outclassed by your cell phone.
Talk about HPFM.

* for those who don't recognize: "Electronic Warfare/Electronic Counter Measures"
** "Anti-Submarine Warfare"

Spent my entire professional life in the EW field and take great pleasure to know the stuff we designed over the year is deployed everywhere. Not a plane in the fleet flies without antennas or electronics we designed and built and I'm proud to say a good number if them came from my teams. Many a sub and destroyers also have antenna clusters and arrays we designed and made.
VSWR: Voltage Standing Wave Ratio. At high frequencies you can't directly measure the voltage because it varies over a given length of the wave. So instead you measure the Standing Wave which is what a vibrating guitar string is.
M

Standing Wave Ratio means you measure the ratio if the reflected wave relative to the incident wave. In a perfect design the SWR would be 1:1 or no reflection.
That will be the conclusion of RF 101.
M

matsickma said:

Spent my entire professional life in the EW field and take great pleasure to know the stuff we designed over the year is deployed everywhere. Not a plane in the fleet flies without antennas or electronics we designed and built and I'm proud to say a good number if them came from my teams. Many a sub and destroyers also have antenna clusters and arrays we designed and made.

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(With apologies for veer
The "2 guys" had worked retrofitting B52 avionics in the Rivet Rambler and Rivet Ace programs before setting up EDIS as a US branch of the Italian outfit.
The most fascinating gadget they told me about was a "ghosting" system that received an enemy radar signal, immediately transmitted it back at high power and stored the signal in a time delay mechanism and then re-transmitted at low power and even at varying intervals and power levels.
Practical result was that enemy radar officers would be confused about which return signal out of 3 or more was the actual reflection.
And it was all a game of one-upsmanship about who could generate frequencies too high for the other guy to detect at all.
("I can see you but you don't know it")
I took a lot a of pride that the US was always the winner in that game, and pray we still are..

We now return to our regularly scheduled thread:

"Inductance in guitar pickups: Magic or just another mystery yet to be unraveled ?"

matsickma said:

Standing Wave Ratio means you measure the ratio if the reflected wave relative to the incident wave. In a perfect design the SWR would be 1:1 or no reflection.
That will be the conclusion of RF 101.
M

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Right. He was actually trying verify animals like tunnel diode amplifiers were in spec when actually in a circuit with impedance mis-matches, because of the application.
Then we'd wrap 'em in bubble wrap and a cardboard box, walk 'em to the top floor of a 2-story building and drop 'em in the parking lot, and test 'em again.
That was the "2 G shock test", I kid you not.
:shocked:
(Being solid state devices I don't recall one ever failing or coming back from Italy after they tested again on their end)

A few years into my career I got involved with Expendable Decoys which used the technique you referenced and is often referred as a "straight through repeater". In practice it requires additional signal processing to work in a modern EW environment. Large aircraft, ships, etc., use a combination of chaff, decoys, flares and "spinning mirrors" and on board "repeaters" to protect themselves.
For those interested google "Association if Old Crows". The AOC is a industry EW group. I think in the UK they are know as the Ravens.

Trivia fact: In the first Gulf War the first Iraq fighter downed was downed by a plane with no weapon's?
"How can that be?" You ask.

The Iraq fighter encountered an EF111 Advark. This aircraft was a EW version of the F111 which was the only EW aircraft that could fly supersonic with the F15's etc when doing a SEAD (Suppression of Enemy Defenses) mission. The Iraqi fighter closed in on the Advark. The Advark took evasive action and dove to the hard deck. What the enemy fighter didn't know was the EF111 had terrain following radar capability. As the enemy fighter closed in on the Advark the EF111 turned , leveled out and flew near nap of the earth. The enemy fighter, on the other hand, crashed into the ground and was the first registered bogie downed during the 1st Gulf war!
M

matsickma said:

I think in the UK they are know as the Ravens.

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Kind of fitting as the EF-111 was originally known as the "Raven". (I think the standard F-111 was the "Aardvark")
And I thought they were called Ravens because originally they were going to be painted with black radar-absorbent paint but not finding confirmation of that right now.
Might be confusing it with Have Blue design elements.
Then there was the "Wild Weasel" program in Viet Nam, which code name was applied to several different aircraft over the course of the war, now called "SEAD" which you mention.
The Wild Weasel mission: Make yourself a target so when the enemy radar "lit you up", they made themselves a target for your Radar -homing missiles, thus taking out the targeting capabilities of SAM batteries and smoothing the way for the actual strike flight following.
Now flying those missions "takes a pair", so to speak.. (a pilot and an RIO, or "2 pairs", even)

So I'm taking a wild guess you work for General Dynamics or Northrup, but if you'd have to kill me if you told me I can live with the suspense.
:biggrin-new:

Ahha....tunnel diodes...one of the first practical inventions that came from quantum mechanics! Lasers are also one which we so readily rely upon today...the veer continues.
M

You are right! EF111 was the Raven! My mistake.
Knew guys who flew F105 Wild Weasel missions in Vietnam. Went on to do other things. Was on SAC B52's in the early 70's. In fact the B52's that are are still in service today are the ones with the nukes that did little flying time. They would do drills and roll out on the runway only to be stood down.
This guy said in '72 the Soviets launched two satellites at the same time without announcing it in advance. They were scrambled to get the SAC B52's in the air. Since they were always drilling to scramble he assumed it was just another drill. He was the guy with the keys to open the nuke code safe. The standard drill the plane would taxi down the runway and then stand down. On this occasion the plane passed the normal point. As he walked towards the nuke codes the two armed AF Rangers guarding the codes stepped aside and let him pass. That never happened before. He said he $hit his pants as he proceeded toward the codes! As he was about to open the safe the B52 was stood down.
The Soviets used the unannounced pair of satellite launches to test our responses. And the Cold War game of cat and mouse continued.
M

Tier 0- DOD, Tier 1 companies build the platforms, Tier 2 build and integrate the systems in the Tier 1 platforms. Tier 3 build subsystems, Tier 4 build components.
I work at Tier 3 level. If I did work for the companies you mentioned I would have a pension and be retired today!

matsickma said:

Y"magic" that is proportional to the highest frequency

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Much of my career involved digital signal processing so frequency was not of a direct concern for me. The math was generally the same. I recall with amusement many decades ago when I was working on cutting edge radar and ECM for the Navy and a friend was working on cutting edge sonar for the Navy. The stars aligned and we got a chance to discuss our work in a secure environment. It turns out that what was cutting edge processing for me at radar frequencies was old hat for him at "audible" frequencies. Similarly, his biggest issues had already been solved for radar but the solutions did not work well, in practice in the sound realm.

I also worked for a company that made instrumentation radars which were a major component in the R&D that led to today's stealth technology. Radar cross section (RCS) is a concept that measures how big an object appears to a radar operating at a particular frequency. Simplistically the first step in making something stealthy is to lower the RCS. One of the engineers was complaining that he had started getting a lot of speeding tickets in his new Corvette, especially compared to his old one. Hoods were opened, cars were inadvertently parked on the radar range and a conclusion as reached. From the standpoint of a police radar, the major contributor to the RCS of an oncoming 'Vette is the radiator. The fiberglass body is effectively transparent. In the old Vette, the radiator was mounted at an angle and so many of the incoming radar pulses were reflected "into the air" and not back at the police radar. In the new Vette the radiator was mounted at a 90 degree angle making it the perfect reflector. That change increased the RCS by about an order of magnitude and thus made the job of the police radar much easier.

fronobulax said:

I also worked for a company that made instrumentation radars which were a major component in the R&D that led to today's stealth technology. Radar cross section (RCS) is a concept that measures how big an object appears to a radar operating at a particular frequency. Simplistically the first step in making something stealthy is to lower the RCS. One of the engineers was complaining that he had started getting a lot of speeding tickets in his new Corvette, especially compared to his old one. Hoods were opened, cars were inadvertently parked on the radar range and a conclusion as reached. From the standpoint of a police radar, the major contributor to the RCS of an oncoming 'Vette is the radiator. The fiberglass body is effectively transparent. In the old Vette, the radiator was mounted at an angle and so many of the incoming radar pulses were reflected "into the air" and not back at the police radar. In the new Vette the radiator was mounted at a 90 degree angle making it the perfect reflector. That change increased the RCS by about an order of magnitude and thus made the job of the police radar much easier.

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That's a very cool story. Do you remember which 'vette? Did that information make it to the rest of the world? I imagine people figured that out eventually, but I love that people actually tested it like that.

GAD said:

That's a very cool story. Do you remember which 'vette? Did that information make it to the rest of the world? I imagine people figured that out eventually, but I love that people actually tested it like that.

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I remember reading about the concepts in late '70's-early '80's Motor Trends and Car and Drivers, of radar cross section in general but not specifically about Corvettes.
They were already aware that "wedge shaped" designs (in metal) tended to have better "stealth" due to the deflection of the return signal but that fiberglass was "transparent" (plastic noses were becoming more common).
Also covered the issue of the LE radars being constantly upgraded to higher freqs to stay ahead of the detector makers.

But I'm wondering if "New" meant "new" for HIM, and he'd traded into the first gen from a second or 3rd gen?
First gens have had periods of greater desirability than current models or 2nd gen models especially in early '80's.

First gens ("53-'62) were vertical:


Ssecond gen ("C2", the famous "split-window" Stingray body of '63-'67) started the canted radiator design to allow for the lower clearance:


Also the C3 '68- '82 "Mako Shark" types; C4's, still canted, as far as I can tell they've been canted ever since the 2nd gen although the angles may have changed, particularly because airflow was an issue when they were at too shallow of an angle, that was addressed in the '84 total re-design, smaller, more efficient but a little steeper angle:
This '84 cutaway gives a pretty good idea:


Also for the "C2" cars there were different radiators for the small block vs big-block( needed bigger radiators), and with or without air (which added a second radiator which might have increased reflectivity), or even an oil cooler which hung vertically below the radiator)

First airplane designed by Electrical Engineers: F117 Stealth Fighter (bomber). Second airplane designed by EE's: B2.
What a difference a decade made in supercomputer capability. In the 70's you could on solve the equations on straight surfaces; in the 80's the curved surfaces could be solved.
Also...my son just sent me an article about JSF where they have added a "Luneberg reflector" to raises the RCS signature so airport radars know they are in the area. I had the good fortune to work with a retired Dean of Engineering Science at Penn State on my 2nd job. Apparently he designed Luneberg Lens during WWII. A Luneberg Lens is basically a sphere that has radially varying dielectric or index of refraction (for the optics guys) that varies from high in center to low on the outer edge. It can be used to scan a beam by moving the location of an antenna around its outside diameter. I suspect a Luneberg reflector has a similar property so that the airports radar can now see the F35 as it approaches the airport from any forward angle.

M

For the Corvettes with the vertically mounted radiator an aftermarket Frequency Selective Surface (FSS) grill mounted at an angle will do the trick to defeat the police radar!

So reading deeper from the hyperlink reference in the first article the Luneberg "reflector" and "lens" are one and the same beast. The application is different where the "lens" is used to scan a beam the "reflector" takes a radar wave from a given direction and reradiates it all angles.
M

GAD said:

That's a very cool story. Do you remember which 'vette? Did that information make it to the rest of the world? I imagine people figured that out eventually, but I love that people actually tested it like that.

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There is a lot I don't remember but I'm thinking the new Vette would have been available in '83-'86. The information almost certainly was not circulated beyond people working the project because it would have attracted attention to the project. ;-)