Fun with RADAR

Say 'radar' and most people think of FAA air traffic controllers following airplanes or NASA engineers tracking rockets. But RAdio Detection And Ranging can be used for a lot of purposes including some that are simply fun. Especially when you can put a whole radar system on a 5mm x 5mm chip, like ViaSat managed to do.

If you stand in a canyon and yell, you'll hear an echo when the sound of your voice bounces off the side of the canyon and back to you. Like timing a thunder clap to judge distance to lightning, if you time the echo of your yell and know the speed of sound (roughly a 1000 feet per second) you can estimate how far away the cliffs are (and how close a thunderstorm is).

With radar you essentially do the same thing except you use a radio signal instead of sound, and the signal propagates at almost the speed of light (about 11 inches per nanosecond). Send a radio pulse, listen carefully for an echo, and you can tell how far away something is by measuring how long it takes for the signal to go out and bounce back.

If you know the direction your antenna is pointing when you receive the signal you know where to look for the target. Compute the difference in position between two received signals and you can tell the direction your target is moving.  Measure the change in frequency of your radio signal, and you can determine the speed of the target with respect to your antenna (a target with zero speed may be traveling in a circle around you).

It doesn't take a van full of electronics and a huge rotating array to put radar to work. ViaSat has put the whole thing on a 5mm by 5mm chip. Add a power supply and an antenna and you're in business. It's not quite that easy of course, but that's essentially all you need.

ViaSat doesn't sell their chips retail, but a a similar radar sensor will set you back only about $10. You won't be able to track passing aircraft or bust speeding drivers, but you could create a back-up obstacle detector for your car or an intruder alarm that won't go off if a cat strolls by.

Or, just for fun, you could build a theremin—one of those weird sounding electronic musical instruments. They date back to the 1920s when people used an antenna and oscillator to produce spooky sounds. With a radar chip you could do the same to measure the motion of your hands.


ViaSat's chip is available for military and commercial applications that are a lot more serious, such as perimeter security, traffic management, and altimeters. In such applications the product has to survive challenging environmental conditions, take up up as little space as possible, use a tiny amount of power, and require no tweaking after it's installed—and do all that for a reasonable cost.

ViaSat's radar-on-a-chip is unique. It's the only self-contained frequency modulated continuous wave radar sensor on a single chip. What's more, it can be easily tailored to different applications using digital interface software to control frequency and bandwidth. Best of all, it works over a wide temperature range because it self-calibrates continuously.

With those capabilities, the chip can be used by the military to control vehicles in driverless convoys, provide UAV navigation in tight spaces, or watch for small boat intruders when ships are in port. Civilian applications include adaptive cruise control, already in some cars, so you don't have to brake and reset when traffic slows down.

Radar is just about business and war, it can be fun too.

Satellite Solutions

Technology is always in the news these days, but there's one spectacular device out there you've probably never heard of.

ViaSat-1, launched in late 2011, provides more capacity in one satellite than all other communications satellites over North America combined. It will help 1,000,000 technologically deprived web surfers on the ground, in the air, and on the high seas join the 21st Century.

If you rummage around online forums about broadband services you'll find grumps who complain that satellite services can be interrupted by something as common as rain. That used to be true, but engineers have found a solution so the ViaSat Exede service will do just that— exceed your expectations. Now it's just silly to worry about weather effects except under the most extreme circumstances.

Jim Petranovich, MIT grad and Chief Geek at ViaSat subsidiary Enerdyne, wrote a technical  whitepaper that discusses the ways ViaSat reduces and prevents the affects of weather for users of the company's very special Ka-band (high frequency) satellites. I’ll translate the paper for you, but first a little background.

Bit buckets and fire hoses

ViaSat's high-capacity satellite uses spot beams to concentrate energy into smaller areas than conventional satellites. ViaSat-1 has 72 spot beams supported by 20 gateways. Each spot beam supplies nearly as much bandwidth as one entire old satellite. That means they can send more data, at a faster rate, to smaller user antennae.

Four spot beams on the satellite are usually supported by one ground station called a gateway. The gateways, connected to the Internet, beam data up to ViaSat-1. The satellite acts like a U-shaped pipe that collects a stream of data coming up and shoots it back down to you, wherever your bit bucket (antenna) is located to catch the data. In fact, ViaSat-1 is referred to, technically, as a bent-pipe satellite.

As an aside, the amount of energy an antenna can collect is based on size or aperture. The bigger the antenna—the bigger the bucket—the more energy they collect. So for very strong sources you don't need much aperture. A fire hose will fill a milk bucket, real quick like.

Telescopes work the same way--in a sense they're antennae too, photon buckets, receiving light energy instead of radio energy. That means I can use my little 3.5" telescope to look at the literally blinding Sun, and even need to add a special solar filter, like super-strong sunglasses. My 8" telescope collects over five times more light, so I can use that to observe dim deep-sky objects.

What's all that mean to you? ViaSat-1 has powerful transmitters, brighter or "hotter" than old satellites'. So your antenna only needs to be two and half feet in diameter--a Very Small Aperture Terminal or VSAT. In fact, ViaSat has a battery powered portable terminal for news-gathering organizations that packs into a suitcase that weighs under 50 pounds, antenna and all.

And, now, back to the weather. ViaSat can't make it stop raining, of course, but they have done something about how weather affects broadband satellite services.

Heavy rain,  I mean heavy rain such as in Hurricane Sandy, or a blizzard of wet snow (such as in Hurricane Sandy), can be an issue—light rain and dry snow not so much. Gases in the atmosphere, clouds, and weird changes in the ionosphere, called scintillation, can reduce the strength of a satellite signal too, but those effects are small.

Singing in the rain 

So how does ViaSat make sure even the worst weather doesn't affect your Facebook or Twitter experience?

To begin with, ViaSat-1 is "hotter" than older satellites, as we've said. With stronger down link signals, the reduction in strength caused by weather is less noticeable. Think of weather as blue food coloring and the satellite beam as a stream of water. If you add the coloring to a dribble from a faucet the water will be very blue. Put the same amount in our fire hose, and you won't even notice. Strong satellite signals simply overwhelm small weather effects.

Rain (virga) near Sedona AZ                                    © T Harnish
This whole issue of the effect of rain on radio signals (satellite or terrestrial) has been studied to death. Researchers can tell you how raindrop size, drop oscillation, the angle the rain comes down, and temperature, impurities and host of other nitty-gritty details can affect reception.

But, to be clear, you'll seldom, if ever, notice weather issues using ViaSat's Exede service.  One reason is that really heavy rain, strong enough to be a problem, is a rare event. Another reason weather is seldom a problem is that fancy network protocols (software sleuths) are used to detect and retransmit missing data.

In the case of streaming video, Internet applications expect micro-interruptions anyway, so the computer programs create a buffer that can be emptied while data is resent. They work like your water heater where a tank (buffer) of hot water is created so you can drain it off when needed without waiting for it to get hot. That's why you often have to wait for a YouTube or Netflix video to start, they're filling a buffer.

Okay, you say, but what if the weather is really awful, hurricane awful, and they're looking at the real possibility of signal fade? ViaSat has gotcha covered there too, with some really high tech solutions such as adaptive power control and adaptive coding and modulation.

Adaptive power control generally is only necessary when data is being sent by you to the satellite. Your little dish antenna and small amplifier have to yell most of the time for the satellite far away to hear you. If weather interferes with the satellite, and it's having trouble hearing you, it tells your system to take a deep breath and scream twice as loud for a while to make sure your email to finicky Aunt Martha isn't garbled.

Modern magic

Adaptive modulation, on the other hand, is one of those technologies that, when it's shown in a system diagram, deserves an arrow with a caption that says, "Here there be magic." One of the incantations the magicians use goes something like this: "Euler, Euler, phase-shift, quadraphase; sine wave, sine wave, lowpass, carrier. . .and . . . demodulate." Presto, you have double the bandwidth. But that's just a small part of the show that all happens at the speed of light out in space.

Adaptive coding, including forward error detection, means weather threats just evaporate. Forward error detection sounds like they're not just magicians but psychic too, correcting problems before they happen. But really they're just adding redundancy so your data doesn't have to be retransmitted. It's kinda sad all that magic is going on up there and we can't see it.

Like all magic, there's slight of hand at work behind the scenes at ViaSat, and it's fully understood by those in the know. All you need to know is that fancy software can adapt to changing conditions to adjust your instantaneous data rate and the amount of time the satellite allocates to your messages. You're not even aware anything changed.

Weather can potentially affect gateways, too, of course; and that can be a big problem because everyone supported by the gateway would be affected. But gateways use adaptive power control and adaptive modulation and coding, too. In some cases multiple gateways serve the same spot beams and end users. If weather threatens one gateway, another can be pick up the load without any interruption—more magic developed by ViaSat.


Another nifty trick that ViaSat uses is to put their ground stations outside the coverage area of the spot beams. So while it may be pouring where you are, say in the Gulf Coast or Florida, your gateway might be basking under clear skies in Albuquerque or Tucson.

The moral of the story

Even if it is raining on the gateway, by the way, signal strength is only loosely related to rain intensity. The signal path is generally on a diagonal up from the ground to the satellite located over the West Coast. In any event, the weather at your location has more effect on performance than at the gateway because they have big honking antennae and you just have the little dinky dish.

So you may have filed away in your brain that satellite broadband really isn't a good option because of weather problems. That's not the case anymore. That thought is just brain sludge, taking up space in your noggin along with the 1962 hit tune, Telstar performed by The Tornadoes.

Robot Wars

Our robot took its first steps today. Now there's a line I never thought I'd write. I read more science fiction than most people, I suspect, but somehow I never really thought I'd own a robot. But I do.

Come to think of it, this baby is our second. Several years ago we bought an iRobot Roomba.


Rommba sucks, but that's a good thing for a vacuum cleaner. In fact, it works very well indeed, and while initially we thought it was kinda expensive, it definitely has earned its keep, wandering around nibbling odds and ends and scarfing down cat hair. When it gets caught under the sofa it bleats, "Oh-oh" a few times, and then patiently goes to sleep until we rescue it. Free to roam, it even heads home to find its docking station when the battery runs low and it needs to literally recharge its batteries.

But the second little bundle of joy came into out lives when my son, in a geneologically confusing sorta way, gave us a brother for Roomba—iRobot Create. We call him Vroomba because of the way he tears around. Here you see a sibling decked in full regalia for a Popular Science contest. But why we call ours Vroomba needs some esplainin'.


To begin with, it took some effort—almost entirely dealing with @#$%^* Microsoft's operating system, but our robot recently took its first steps. I'm a proud Daddy, of course, because everything Vroomba knows, I taught him. At least if you don't count the low level machine language code embedded in his hardware. They're kinda like instincts, programmed in and all.

It took several hours over the last few weeks to figure out some arcane details of his serial COM ports. Setting them to 56700 baud, 8 bits, 1 parity bit, and no flow control was, by comparison, an easy task thanks to telephone modem experience back in Apple ][+ days. (Remember when 1200 baud was fast?)

Then I had to hook up a serial port adapter, which I fortunately had for a telescope, because the interconnect cable that came with it had a 9 pin DIN plug on one end and a standard serial plug on the other. But, of course, the adapter had its own drivers that had to be installed and configured. And of course @#$%* Microsoft did me a big favor and assigned the adapter to port 4, but it needed to be on 9.

Anyway, I finally figured out the solution to that, and then . . . nothing.

The computer and the robot did not play well together. Maybe the robot was deaf and maybe the computer was mute, but the result was they weren't communicating.

So yesterday was a day off, I rummaged around the web, and found a trial version of a commercial software package that tells you everything about what's going over all the COM, USB, BlueTooth, and any other comm links you might have on your computer. I installed it and discovered, guess what, they weren't communicating. Duh. Hell, I knew that.

Now what?

At the moment I was ready to punch the computer right in the faceplate, the blue screen of death popped up and it died. Voodoo in action?

After a reboot, I cranked up the serial port monitoring program again, and idly typed in the same commands remembering that the definition of insanity is doing something over and over and expecting different results.

But it worked, there was traffic on the line. The message sent was the message received. If only it was so easy in a marriage!

Intoxicated with success, I sent the robot a short command to euphemistically open its eyes (blink a light).

And it did!

I danced the cat around the room in joy.

Casting caution aside, like a scene from a scary movie, I sent a string of commands to get Vroomba's attention, tell it what direction to move, and then sent a command that essentially meant, "Let's roll."

And it did!

Vroom was off!

Poetically, it promptly ran into a huge 1200 page book titled Windows XP Inside and Out that I'd thrown on the floor in disgust. The tome slowed Vroomba up a bit, but he dug in and pushed and pushed. I yelled encouragement, I clapped my hands, and then I needed a towel.

No I didn't wet myself. The robot serial cable dragged my beer off the edge of the table. And the bugger didn't even stop to say he was sorry. He just trudged on, and on, and on. The Energizer bunny personified, er . . . robotified.

But, as Isaac Asimov would have wanted, Vroomba unplugged himself and ground to a halt before he dragged my computer into the next room.

Today? Who knows, we might dance a jig and play music. But I need to keep an eye on him. Don't want Vroomba to catch a virus. His immune system isn't very robust.

Tomorrow? The sands of Mars or the mud of Titan!