How do you fix a shorted cable ? Not just any cable. An underground, 3-phase, 230kV, 800 amp per phase, 10 mile long one, carrying power from a power station to a distribution centre. It costs $13,000 per hour in downtime, counting 1989 money, and takes 8 months to fix. That’s almost $75 million. The Los Angeles Department of Water and Power did this fix about 26 years ago on the cable going from the Scattergood Steam Plant in El Segundo to a distribution center near Bundy and S.M. Blvd. [Jamie Zawinski] posted details on his blog in 2002. [Jamie] a.k.a [jwz] may be familiar to many as one of the founders of Netscape and Mozilla.
To begin with, you need Liquid Nitrogen. Lots of it. As in truckloads. The cable is 16 inch diameter co-axial, filled with 100,000 gallons of oil dielectric pressurised to 200 psi. You can’t drain out all the oil for lots of very good reasons – time and cost being on top of the list. That’s where the LN2 comes in. They dig holes on both sides (20-30 feet each way) of the fault, wrap the pipe with giant blankets filled with all kind of tubes and wires, feed LN2 through the tubes, and *freeze* the oil. With the frozen oil acting as a plug, the faulty section is cut open, drained, the bad stuff removed, replaced, welded back together, topped off, and the plugs are thawed. To make sure the frozen plugs don’t blow out, the oil pressure is reduced to 80 psi during the repair process. They can’t lower it any further, again due to several compelling reasons. The cable was laid in 1972 and was designed to have a MTBF of 60 years.
Let’s start off with proof. Below is an animation of a measurement of airplanes and meteors I made using a radar system that I built with a few simple easily available pieces of hardware: two $8 RTL software defined radio dongles that I bought on eBay, and two log-periodic antennas. And get this, the radar system you’re going to build works by listening for existing transmissions that bounce off the targets being measured!
I wrote about this in a very brief blog posting a few years ago. It was mainly intended as a zany little side story for our radio telescope blog, but it ended up raising a lot of interest. Because this has been a topic that keeps attracting inquiries, I’m going to explain how I did the experiment in more detail.
It will take a few posts to show how to build a radar capable of performing these types of measurements. This first part is the overview. In later postings I will go through more detailed block diagrams of the different parts of a passive radar system, provide example data, and give some Python scripts that can be used to perform passive radar signal processing. I’ll also go through strategies to determine that everything is working as expected. All of this may sound like a lot of effort, but don’t worry, making a passive radar isn’t too complicated.
If you’re a ham, you already know that the ionosphere is a great backboard for bouncing HF signals around the globe. It’s also useful for over-the-horizon backscatter (OTH-B (PDF)) radar applications, which the United States Air Force’s Rome Laboratory experimented with during the Cold War.
During the trial program, transmit and receive sites were set up ninety miles apart inside the great state of Maine. The 1/2 mile-long transmit antenna was made up of four arrays of twelve dipole elements and operated at 1MW. An antenna back screen and ground screen further expanded the signal’s range. Transmission was most often controlled by computers within the transmit building, but it could also be manually powered and adjusted.
The receive site had 50-ft. antenna elements stretching 3900 feet, and a gigantic ground screen covering nearly eight acres. Signals transmitted from the dipole array at the transmit site bounced off of the ionosphere and down to the receive site. Because of step-scanning, the system was capable of covering a 180° arc. OTH-B radar systems across the continental United States were relegated to storage at the end of the Cold War, but could be brought back into service given enough time and money.
This year’s Hackaday Prize is heating up, and right now there are quite a few projects in the works covering domains that are rarely, if ever, seen coming out of a garage or a workshop. One of the most interesting is [Glenn Powers]’ Open Ground Penetrating Radar. It’s exactly what the title says: an open-source radar system that can see into the Earth for less than $500.
While ground penetrating radar is great for archaeology and people searching for hoards buried in the middle of farmland, the biggest application is safety. You need only to Google “Florida sinkhole” to see the value of peering into the Earth.
[Glenn] is building his ground penetrating radar with a bare minimum of parts. A Baofeng VHF/UHF My First Radio™ serves as the signal generator, the controller is just an optoisolator, and the switch controller is a 7404 hex inverter. It literally can’t get simpler than that.
Of course these components can only be assembled into a simple radar, and the real value of a ground penetrating radar is the ability to map an area. For that, [Glenn] is bringing out a Pi and a GPS dongle to control the whole thing. Visualization is provided by none other than the US Navy. If it works for submarines, it should work for a metal cart, right?
It’s a great project, not only in the fact that it could help a whole bunch of people, but as a prime example of doing so much without tens of thousands of dollars in test equipment.
It’s been said that the best defense is a good offense. When aloft and en route to deliver a harmful payload to the enemy, the best defense is to plan your approach and your exit carefully, and to interfere with their methods of detection. If they can’t find you, they can’t shoot you.
As of May 1962, the United States military was using three major classifications of radar jamming technology as described in this week’s film: the AN/ALQ-35 multiple target repeater, the AN/ALQ-55 communications link disrupter, and the AN/ALQ-41 and -51 track breakers. The most important role of these pieces of equipment is to buy time, a precious resource in all kinds of warfare.
The AN/ALQ-35 target repeater consists of a tuner, pulse generator, transmitter, and control panel working in concert to display multiple false positives on the enemy’s PPI scopes. The unit receives the incoming enemy pulse, amplifies it greatly, repeats it, and sends them back with random delays.
The AN/ALQ-55 comm disrupter operates in the 100-210MHz band. It distinguishes the threatening enemy communication bands from those of beacons and civilians, evaluates them, and jams them with a signal that’s non-continuous, which helps avoid detection.
Finally, the AN/ALQ-41 and -51 track breakers are designed to break enemy lock-on and to give false information. It provides simultaneous protection against pulse ranging, FM-CW, conical, and monopulse radar in different ways, based on each method’s angle and range.
Until recently phased array radar has been very expensive, used only for military applications where the cost of survival weighs in the balance. With the advent of low-cost microwave devices and unconventional architecture phased array radar is now within the reach of the hobbyist and consumer electronics developer. In this post we will review the basics of phased-array radar and show examples of how to make low-cost short-range phased array radar systems — I built the one seen here in my garage! Sense more with more elements by making phase array your next radar project.
Phased array radar
In a previous post the basics of radar were described where a typical radar system is made up of a large parabolic antenna that rotates. The microwave beam projected by this antenna is swept over the horizon as it rotates. Scattered pulses from targets are displayed on a polar display known as a Plan Position Indicator (PPI).
In a phased array radar (PDF) system an array of antenna elements are used instead of the dish. These elements are phase-coherent, meaning they are all phase-referenced to the same transmitter and receiver. Each element is wired in series with a phase shifter that can be adjusted arbitrarily by the radar’s control system. A beam of microwave energy is focused by applying a phase rotation to each phase shifter. This beam can be directed anywhere within the array’s field of view. To scan the beam rotate the phases of the phase shifters accordingly. Like the rotating parabolic dish, a phased array can scan the horizon but without the use of moving parts.
SAGE was developed at MIT’s Lincoln Laboratory on computers built by IBM. It used the AN/FSQ-7 in fact, which was The Largest Computer Ever Built. SAGE operated as a network of defense sectors that divided the continental U.S. and Canada. Each of these sectors contained a directional center, which was a four-story concrete blockhouse that protected and operated a ‘Q7 through its own dedicated power station. The SAGE computers employed hot standby processors for maximum uptime and would fail over to nearby direction centers when necessary.
Information is fed into each directional center from many radar sources on land, in the air, and at sea. The findings are evaluated on scopes in dimly-lit rooms on the front end and stored on magnetic cores on the back end. Unidentifiable aircraft traces processed in the air surveillance room of the directional center are sent to the ID room where they are judged for friendliness. If found unfriendly, they are sent to the weapons direction room for possible consequences.