Mainly I work in the area of airliner collision avoidance systems, known generally as "TCAS", which I think stands for "Traffic Alert and Collision Avoidance System". As an oversimplification, it's a two-part system, with each aircraft being equipped with a transponder and a TCAS interrogator. There are a bunch of different modes and sub-modes, but fundamentally an interrogator transmits an encoded signal that basically reads "Who are you and how high are you?" The transponder receivers the interrogation and transmits a reply that basically reads "This is me, and I'm at 15,000 feet."
The TCAS interrogator then works out the approximate range by which whisper-shout step triggered the reply and the approximate bearing by differential signal strength and phase as seen by four directional antennae. It then does some spooky math on all this and determines if the "intruder" (as the replying airplane is known) is too close or likely to get too close in the near future (and if so, it has what I like to think of as a "conniption fit" and instructs the flight crew to take evasive action - when the voice advisory system is working, you get all sorts of interesting voice messages, like CLIMB! CLIMB NOW! CLIMB, CROSSING, CLIMB! And then, at the very end, the meek little Clear of conflict... Voice advisory is a whole 'nuther subject. One of the voice messages you can get is the mysterious word "MINIMUM", which I believe is announced as the aircraft is nearing its decision height in an instrument approach, or perhaps decelerating toward its minimum safe flight speed, I'm not sure, though I think that one gets you "AIRSPEED". Anyway, a woman at work once asked me "Why does that thing keep saying enema, enema?")
It's more complicated than it sounds, especially when everything is working in full Mode-S mode and transferring data back and forth by means of DPSK modulation (I've always had this odd "wouldn't it be a fun world" fantasy where women are more impressed by the fact that I know that DPSK stands for differential phase shift keying than by some guy's fancy-shmancy Corvette, and where they say "Is that a long Mode-S interrogation you have there, or are you just happy to me?").
Anyway, among other things I design the hardware used to test and calibrate all this stuff, and write the software that runs the tests themselves. It's fun, except that the airways are now so crowded that there's a constant barrage of interrogations and replies flying back and forth. All of this traffic makes it hard to perform certain tests - when you're trying to get the unit to reply to a single interrogation while everyone else on the planet is transmitting away, well, it can be a mess. Synchronous garble is fun. Weird FRUIT is even more fun. I'm not exactly sure what FRUIT stands for - I've seen at least two different versions, but I prefer False Reply Uncorrelated In Time, meaning a reply that comes at a time when one is not expected...
The short version of all this hoohah is that to get a quiet enough environment (from a radio frequency point of view) it is sometimes necessary to set up your equipment and run your tests in a screen room. A screen room is just a metal room, almost always copper, usually either solid or what looks like window screen made out of copper. The power feeds have special filters, and even the air conditioning ducts have special traps in them that in some cases look like metal honeycombs, specially sized to reject radio signals at a particular frequency (in my line of work, the frequencies of interest are 1030 MHz and 1090 MHz). The doors are usually solid metal, and are secured with mammoth latches that wouldn't seem out of place on a battleship.
The point is that these screen rooms are like submarines. Once you're in and the door is latched, you're in your own private world. You can't see the outside world. You can't hear the outside world. Your cell phone doesn't have any bars at all. Wireless network devices don't work. And for some reason, such screen rooms are always either insufferably hot or bone-chillingly cold. I've worked in both. The hot ones are like being in a sauna; at the end of the day you're sweaty and kind of ripe, and all you really want to do is go home and take a shower. The cold ones are worse, if anything - your body takes on a deep, persistent chill that's very hard to break. You know your screen room is too cold when you go outside in a Phoenix summer just to warm up. And I note that ever since chemo, I'm much more sensitive to cold, though I tend to blame everything on chemo. "I dropped a hammer on my toe; damn I hate chemo!"
I've been working nights lately, meaning for the last couple of months. There are two real reasons for this. The first is that there's only one test station, and two different groups of people want to use it (Production, so they can test and ship boxes and make money, and me, so I can develop the remainder of the tests). The second is that there's less air traffic in general at night. In particular, the VFR traffic at the nearby airport stops, so there's just less of a mess in the airwaves. Though I don't think you need a transponder for strict VFR operation, they always do, and they're always a-squittering away in Mode-A or Mode-C, either of which can cause synchronous garble with Mode-S ("Crap! It missed three replies! I wish those flight students would turn off their transponders!") (One of the unsolved mysteries in this whole ATCRBS (Air Traffic Control Radar Beacon System) business is why an unsolicited reply is called a "squitter". But sometimes when someone tells me something I didn't want to know about, I catch myself thinking "Oh great, he's squittering again.")
My point, really, is that working nights in a copper screen room is doubly isolating. I hardly see anyone at all in the span of any given week. There are a few people loitering around the place in the late afternoon when I get there, but otherwise, it's just me, the cleaning crew, and the night guard. And since they are not typically fluent in English and I am not fluent in Spanish, there isn't much opportunity for conversation beyond the occasional friendly nod. It's just me and my Finnish and Polish death metal.
So those are my workdays lately: bone-chilling cold and levels of isolation that probably rival those of a nuclear submarine on patrol. But hey, at least the traffic is pretty light going home.
So the next time you're on approach to some airport and you sense that your airplane suddenly stops descending and climbs a little bit, look over at the passenger next to you and say "DPSK, you know..."
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