MF – Medium Frequency, specifically 2.7 MHz, given or taken a Hz.
This toy is another one of the projects under my jurisdiction and the one that annoys me the most.
First, what do we do with it. Well, our atmosphere is composed of several layers, like a vulgar pile of delicious pancakes made with different types of flours. It happens that one of those layers, or better, the transition between two of them, is particularly sensitive to radiation between 2 and 3.5 MHz. This means that it is possible to light up whatever lives in that area with this radar. Just like the visible radiation that we depend upon to see where we put our feet and avoid head butting walls, radars also work by sending light (electromagnetic radiation) towards objects and analise what we get back in case there are reflections. It is what we do every day in airports: those big antenas that stand out in the landscape are continuously sending pulses of light into the sky.
Any airplane that enters the action radius of this radar is going to reflect it and on the air controller’s screen a dot appears. For us dumb humans, its all the same because these radars use a type of light with a frequency out of the range that we can detect. Its kinda like those dog training whistles where the poor pooches almost scream with pain yet we can’t hear a thing. That because dogs can detect sounds with frequencies above the human limit and these whistles work in that area. In a very, but really very simplistic fashion, this is it. But if we barely have birds around here, let alone planes or UFOs, what the deuce are we then lighting with this radar? The only thing that we can: winds.
The layers that we can see with this radar are situated between 60 and 100 km of altitude (for reference, comercial flights go around 10 km and a weather balloon in a really good day can reach 30 km in altitude).
In this zone, most of the molecules that compose the atmosphere are ionized by absorbing the sun light, i.e, they have some of their electrons ripped off by it, which turns them into sort of mirrors for any light coming from “bellow” in the frequency interval that I’ve mentioned above.
Winds in this area are particularly influenced by the Sun’s mood, the position of the Moon in the sky and other movements from the lower layers of the atmosphere. And that’s pretty much this: the radar works as a big lamp that sends light into space. Some of that light bounces on the things that we want to study and gets back to the radar and that’s how we “see” them. The rest is just science.
It seems simple but the fact of us being in Antarctica, and on top of an ice shelf from all places, turns this radar into something quite troublesome.
Since it works with a relatively low frequency, the antennas used to transmit these 2.7 MHz of light are gigantic, specifically, each is 60 meters long. Its one of those science and engineering things: lower frequencies require big antennas and vice versa. Its all about the light’s wavelength, something that grows as the frequency diminishes and the other way around too. Let’s not go down there for now.
For example, wifi routers that we have around the house have small antennas, 10 or 15 cm tops. This is because they operate in the GHz band, that is, a frequency thousands of times higher than the one in this radar, and as such the router’s antennas are thousands of time smaller.
Another great example: mobile phones. The first generation ones (the bulgy ones that could be used as deadly throw weapons) worked in a frequency slightly higher than the one that the wifi routers use. They had antennas sticking of the back and in some you had to push it from its insides to make a call. As technology progressed, mobile networks started to use higher operation frequencies (the whole 2G, 3G, 4G mumbo jumbo that everyone was talking about a few years ago). Higher frequencies mean higher data rate (and that’s why today we can stream cute cat videos on our phones while 15 years ago we were barely able to send texts) and smaller antennas. Today’s phones have antennas so small that they just stuck them inside of it and we can avoid getting pricked by it when we bend over with out phone in the pocket.
This radar is over a kilometer away from the station, in order to run away from the electromagnetic noise of the modules. Its 20 to 25 minutes on foot in Winter, when is too cold to start a skidoo. In its essence, the antennas are nothing more that a steel wire segment, suspended about 4 or 5 meters from the ground by telegraph poles, like the ones that used to hold the old telephone lines, connected to a centre pole where a very thick and heavy coaxial cable brings the signal to transmit from a control booth where all electronics and system controlling computer is.
Around here we call these booths “cabooses” and they are basically half of a metal shipping container suspended over steel legs (so it doesn’t get all buried in Winter).
To allow the electronics inside to work without pain, these cabooses (we have 6 of those here) are acclimatized. They are reasonably well isolated and are warmed up to a nice and cozy 16 ºC, give or take a degree. In Winter they work as an oasis of sorts. I’ve happen to be fussing around the area one of these days and got my fingers all blue and numb. Fortunately I had one of these cabooses just 100 meters away and I could defrost all my extremities without having to suffer for half hour until I could get back to the modules.
The radar is composed by 5 antennas, each with two 60 meters segments crossed between them. In total its around 600 meters of antenna and there’s where most of my work with this thing resides. The length of each antenna is very specific, each one carefully tuned to transmit at 2.7 MHz, just like the old pocket FM radios. But this is Antarctica, a place where ice can form easily in one’s eyelashes.
The antenna wires are not an exception. Here, all it takes is the relative humidity in the air to rise a bit, or getting a visit from Mr. Fog, something that happens every other day in Autumn, and these antennas get covered with a good centimeter of ice around them.
Unfortunately this ice changes the antenna properties in such a way that the radar is forced to turn off itself so it doesn’t start to smoke… literally. We need a considerable power to reach 100 km in altitude with our signal and get reflections strong enough to be detected back down. 120 kW of it to be more precise. As long as the antennas are decently tuned, a big chunk of this power is transformed into electromagnetic radiation (light) and send into space, as it is supposed. But too much ice in the wires throws them out of tune and that means that a significant part of that energy is reflected back into the transmitters. More ice means more reflected energy instead of being sent to the upper atmosphere. To prevent these reflection from frying the sensible components in the receivers, the control computer is continuously checking the reflecting index of the antennas and only transmits if this one is bellow the maximum allowed.
What happens then if the antennas get too icy? Well, in those circumstances, a special metal surface ice removal system is activated, which is pretty much a cranky and cold engineer armed with a really long rope.
Super complex method for removing ice from antennas: the engineer throws one end of the rope over the antenna and then drags the suspended rope over each and every one of the 600 meters of antenna cable, while chunks of falling ice hits him in the face and inside that small space behind the neck, something rather pleasant at -40 ºC.
Its the same principle behind dental floss, but a lot more slow and uncomfortable. In average it takes me 40 to 45 minutes to clean everything. With the trips from and to the modules and a configuration here and there before resuming the radar operation, its around 2 hours of this every other day.
Autumn was particularly annoying. Summer was peaceful. Even if some ice formed during the short nights, the morning Sun was more than enough for it to melt and fell off them by its own weight. But as soon as the Sun went away, disaster struck. Autumn here is characterized by peaks in air relative humidity, when the wind blows from Northwest and brings all the moisture from the ocean to here. Sometimes the radar stops for several days while Halley is buried in fog banks after fog banks, some so thick that visibility gets reduced to a few meters. Winter wasn’t all that bad since every now and then we get a really nice storm. What’s so good about storms? 85 km/h winds that’s what! Those babies clean the ice right out of the antennas better than I could ever do.
Last Autumn this work reached such an annoyance level that one of my buddy’s here, inspired by my desperate look while preparing to go to my 71st defrosting run on the antennas in May, composed a nice poem/rap lyric about it and stuck it in my room door:
Oh well, I guess its nice to run away from the comfort and warmth of the modules every now and then…