Chasing RFI Waves – Part One

Back in 2005, I started writing what I’d planned to be a non-fiction book about NRAO (the National Radio Astronomy Observatory), based on visits, photos and interviews to that very interesting place. My contact was Wesley Sizemore, NRAO’s public face and “Keeper of the Quiet”, a term which will make more sense to you once you read more about NRAO and the NRQZ (the National Radio Quiet Zone).

I didn’t get to finish the book. Life intervened, I got caught up in other things and my photos, interviews and written pages (there are quite a few of them) sat in my Documents folder, gathering digital dust ever since (it’s been about seven years now).

Rather than let it all sit there till oblivion, I thought it’d do more good published, unfinished as it is. If I ever get the chance to make subsequent visits and finish writing the whole story, great. If not, here it is for your enjoyment. NRAO is a neat place doing interesting research into things that have always obsessed humans: outer space, planets, aliens, etc.

I am deeply indebted to Wesley Sizemore for this work. He welcomed me to NRAO with his wife, Sherry, who also works there, and took precious time out of his schedule to talk with me at length and drive me around the campus in order to show me the various telescopes. He was patient, welcoming and incredibly informative. The book is based, by and large, on my recorded interviews with him. I wouldn’t sound nearly as smart as I do below if it weren’t for his detailed explanations of these arcane concepts.

I also need to make it clear that the book isn’t finished. Some sections aren’t filled in properly. As I wrote them, I had more questions that would get clarification only during subsequent visits, which never materialized. So please forgive whatever rough edges you find, including my barely adequate photos, since I was also at the start of my photographic career at the time.

I’ll publish a section of the book here, every Sunday, until it’s done, so don’t forget to check back every week in order to catch up on each installment. Here’s part one. You can also read parts two, threefourfivesix and seven.


Preface

It was 1:22 pm on the 4th of September, 2005 that I visited NRAO (The National Radio Astronomy Observatory) with Ligia (my wife) and Chris and Lis, good friends of ours. We had just spent the weekend in a rustic cottage on the Greenbriar Trail in West Virginia. We had a lot of fun cycling on the trail and going up the mountains in the C&O Scenic Railroad, but I was disappointed about the lack of cellphone signal everywhere. This was due to the entire area being in what is known as the National Radio Quiet Zone (NRQZ).

We’d had a real adventure finding the cabin earlier that weekend. With road signs sparse and a pitch black night to boot, Ligia and I spent a few hours hunting down the route. We couldn’t use our cellphones and the few public phones we found weren’t working. We made it in the end, but a few choice words were rolling around on my tongue about the “Quiet Zone” during those hours.

When we checked out of the cabin a wonderful weekend later, Chris proposed we visit NRAO with them to find out more about the Quiet Zone. The prospect of a straight four-hour drive back home to DC wasn’t too appealing, so Ligia and I readily agreed we would stop at the Observatory for the tour, to give us a well-needed break from sitting in the car.

There we were, in the parking lot. The sun was out, but an icy cold wind descended from the surrounding hills and chilled us to the bone. Maybe it’s the Florida in me, but I can’t take winds like that, so I scampered inside the building like a scared puppy.

I can’t describe how different this place is from the surrounding WV fare, but it’s readily apparent when you drive through there. You’ve got your farms and forests and hills and mountains with snowy caps, and fields of corn or other crops, plus the occasional redneck sighting (rusted cars, mobile homes in various states of decay, etc.) and then there’s NRAO, a modern stone and glass building. Just the fact that the door slides open as you approach it is a wondrously surprising thing after you’ve taken in the low-tech surrounding countryside. Here I need to clarify that the sliding doors are mechanical, not automatic — automatic sliding doors produce RFI (Radio Frequency Interference), which is to be avoided at NRAO.

Having had a bad customer service experience at one of the WV state parks that weekend, I fully expected the staff there to be unaccommodating, and I was pleasantly surprised when we were invited to join the tour even though it had already started. Into the auditorium we went, happily staking some cozy seats and settling down to enjoy the presentation.

It was that presentation, dear reader, that sparked the idea for this book. Two little stories mentioned during the presentation were simply too interesting to pass up. You see, the folks at NRAO not only “listen” to the stars, they’re also on the lookout for the rogue toaster or thermostat or odd electric heating pad for the pooch. When things such as these are broken, they emit RFI (Radio Frequency Interference) waves, and they can be “heard” for miles around. They actually have folks who are dispatched at the first notice of such waves, and they drive around, Ghostbuster-style, chasing waves with scanners and other high tech equipment. Once they’ve found the source, they look for ways to banish them. The stories of their adventures are in this book, and I hope you will agree with me that they were begging to be published.

A Little Background Information

Let’s get a little wonderful knowledge under our belts! The terms and issues I’m going to briefly address here will help you understand the stories a little better. You’ll be in the know, and you’ll be able to thumb your nose at the initiated who wonder what an omni-directional antenna is. Think of this as your own personal decoder ring to the world of NRAO.

Radio astronomy is a very young science. It all started in the 1930s with Bell Telephone Labs, and noise on their long-distance phone lines. They assigned one of their engineers, Karl Jansky to the problem. His directive was to, simply put, get rid of the noise.

Karl built an antenna like the one that sits in front of NRAO. It looks at low frequencies along the horizon. Using that antenna, he discovered that the radio interference affecting the phone lines was coming from three sources: local thunderstorms, distant thunderstorms, and from the center of the Milky Way galaxy. It was pretty easy to determine the first two sources. It was a bit trickier to find the third.

It just so happened that bursts of interference from the Milky Way galaxy came several minutes later each day. He started asking other folks why that was happening, and they said, “Oh, that’s sidereal time!” Side-what? That’s what I thought too, when I heard it. It turns out “sidereal time equals the right ascension of any point on the celestial sphere crossing the meridian at a given moment.” (Definition obtained from this web page, which is now defunct.)

More confused? So was I. In layman’s terms, this means the time at which a certain star is at its highest point in the sky, and this will vary each day, because of the various movements and rotations of heavenly bodies, of which we are one. Alright, so that explains why the bursts showed up later each day. But what to make of them? Well, that’s where a telescope came in handy. Using his dandy new antenna along with it, he started watching the skies. Sure enough, when the Milky Way galaxy came into view, he started getting bursts of energy on his antenna. Bingo! He made the front page of the New York times with that little tidbit of information, back in 1937!

By the time he completed his research, WWII was starting. All of the research efforts shifted toward the war and everyone forgot his work, except for one gentleman. His name was Grote Reber. Mr. Reber is considered the father of Radio Astronomy. Why? Because he followed up on Jansky’s research and made the first serious discoveries in the nascent field. Being a radio amateur, he wanted to confirm Jansky’s work, so he built a larger dish, made mostly of wood – this same dish is now sitting in front of NRAO as well. He discovered that not only was interference coming from the center of the Milky Way galaxy at the frequency that Jansky was working, but also from other sources, and at other frequencies.

The lucky thing is that by the time Reber was solidifying his research efforts, WWII started winding down. There were a lot of advances made in the field of communications over this period of time, and there was a great big puzzle staring back at researchers: radio signals from space. There was a lot of radar and other equipment left over from the war, so radio astronomy had the tools to be off and running.

Some of Grote Reber’s work, including his machinery, is on display at NRAO. He built these pieces in such a way that modern engineers still can’t figure out how they work.

Grote Reber lived in Wheaton, Illinois when he did his research, but moved to Tazmania and stayed there until his death. He did that because the area was interference-free at low frequencies, at least from earthly sources.

He had grown up during the depression, and had gotten into the habit of living very sparsely. He would take any food left over from his lunches, wrap it up and take it with him. He was also deaf as a post and couldn’t hear a thing without his two hearing aids.

He was at NRAO for 6 months or so, helping to set up his equipment for display. Mr. Sizemore likened Reber to Galileo. That’s the man’s stature in the field of radio astronomy. When he stayed at NRAO, there were a lot of summer students there, who always crowded around him, wanting to get to know him, asking questions, and when he’d get tired of them, the old gentleman wouldn’t say a word, he would simply reach his ears and “click, click” turn his hearing aids off, then go about his business, oblivious to the incessant chatter of the children. That was the end of the conversation! You couldn’t call him, because he wouldn’t hear you. When he did that, you knew that was it, he was free for the day!

What generates radio signals?

There are two basic mechanisms that generate them naturally: thermal and non-thermal.

The easiest way to think of the thermal mechanism is to think of the structure of a molecule. Use hydrogen as the simplest molecule. There’s a nucleus, and an electron in orbit around that nucleus. If you heat or cool the molecule, the electron will gain or lose energy, respectively. It will make a transition – a jump – from one orbit or energy state to another. When it’s heated, it’ll jump to an outer orbit, and when it’s cooled, it’ll come back down to an inner orbit. When it makes one of those transitions (either going up or down in orbit/energy) it will generate a very specific radio signal. That radio signal is unique to the transition of that electron on that molecule.

Hydrogen is the most abundant molecule in the universe. It’s also the simplest molecule. All of its signals – at rest frequencies – are from 1400-1427 MHz. If you look at band allocation tables, you find that this band isn’t used by anybody in the world. That is an exclusive passive research band allocated throughout the world. There should be no emitters in that hydrogen band.

Now it gets a little more complicated. Those unique frequency signatures hold true for every molecule, whether it’s hydrogen, helium, formic acid, formaldehyde, water, etc. They all have unique frequencies associated with the transitions of their electrons. When radio astronomers look at a source – it may be some wispy clouds in the sky, or some unique galaxy – they see certain frequencies, and can identify the molecular composition of those sources by consulting “dictionaries” of “electronic signatures”.

We can use a simple analogy to explain this even better. Look at a prism. You can use a prism to break up light into its various colors and get a rainbow where you can say the green is copper, blue is magnesium, the yellow is sodium, and so forth. We can do the same thing with radio signals.

Everything in the universe is moving relative to us and relative to everything else. All of the frequencies are Doppler-shifted to some degree.

Doppler shift is easily understood when you listen to an ambulance as it goes by you. The pitch of the car becomes higher as it approaches you, because the radio waves are compressed, and lower as it gets farther from you, because they’re stretched. We can think of the Universe in those same terms. It’s expanding, so it’s like a balloon on which dots have been drawn. As that balloon’s volume increases, the distance of the dots from the baloon’s center increases, as well as their distance from each other. All of the signals perceived in radio astronomy are therefore Doppler-shifted to some degree.

We can gage how things are moving relative to us because of the Doppler shift. Radio astronomers have observed Hydrogen frequencies as low as 800 MHz, which meant that whatever object in space emitted those frequencies was moving away from us (the Earth) at some enormous velocity. Radio astronomy is now looking for Doppler shifted signals as low as 125-250MHz to identify “the epoch of re-ionization“. Now we have a way through Doppler shift to get a handle on the motion of objects in space. That’s the thermal mechanism in a nutshell.

The non-thermal mechanism has to do with charged particles moving on magnetic field lines. Let’s take hydrogen again. If you have a conglomeration of molecules moving together, they’re bound to bump into each other and knock a few electrons out of orbit. That means we’ll be left with a negatively charged electron and a positively charged ion, floating around in space. The interstellar medium, the space between the stars and galaxies, is not completely empty, although people tend to think of it that way. It is not a total vacuum. There are molecules or charged particles in that medium. This same space is also permeated by magnetic field lines. Let’s look at auroras to help you imagine this. They are created here on Earth when charged particles from the Sun hit the magnetic fields of the Earth and spiral down to the poles. In space, similar magnetic field lines exist, upon which charged particles can move. Now, depending on the velocity of their movement, and their movement itself, they can generate known radio signals. This can be anywhere in the spectrum, depending on their movement. These signals give us a way to study the interstellar medium.

Because these radio signals have traveled great distances in great amounts of time (billions of years), by the time they reach Earth, they are “astronomically” weak – pun intended.

How weak? The typical signal levels that NRAO looks for are 0.000000000000000000000000001 watts! That’s 1 x 10-26 Watts / Hz · m2 or a Jansky. Most of their signals are milliJansky levels – that’s 10-3 Jk!

This might not mean a lot to you until we look at the energy levels of a few common things:

  • Your cellphone needs approximately 1 milliwatt of power to reach its antenna in order for it to register a signal (10-3 W)
  • A cellphone tower broadcasts around 200-300 watts (3×102 W)
  • A lightbulb is 60 watts (6×101 W)
  • A broadcast station operates at 10-30,000 watts (3×104 W)
  • The energy released by rubbing your thumb and index finger together is an enormous amount of power compared to what NRAO looks for when they scan the sky!
  • This last comparison should drive the point home: the energy released by a single snowflake hitting the ground is more energy than has been received from space by all radio telescopes on the face of the Earth since the beginning of radio astronomy!

So, how in the world can they get these weak signals? How can they see them over the man-made noise? There are certain requirements whose details are given below.


And that’s the end of part one. You can also read parts twothreefourfivesix and seven.