perhaps too powerful
Wednesday, June 3 2009
This morning my "sunburn" on my upper chest had had a night to soak in and it was less comfortable than before. As "sunburns" go, it wasn't severe. But by now I could tell that it hadn't been caused by the sun. It was precisely where it should have been had it been caused by the arc of my stick welder yesterday. I hadn't worn a shirt because I hadn't been seriously concerned that I was putting my skin at risk. I'd taken care to protect my eyes (and thus my face), and other parts of my body (particularly my arms and hands) were suntanned enough to escape burns. But my chest had been exposed like so much film. The actual amount of time that my skin was exposed to light from an arc was probably less than a couple minutes in total, but according to the various sites I read, the ultraviolet light released by the arc of a stick welder is much more intense than anything that reaches the earth from the sun, and the photons are more energetic and destructive. I was lucky to have gotten off with so light of a burn; others I read about online had gotten it much worse. It seems that generally people only make this particular mistake once, which is good because a single bad exposure significantly increases the risk of skin cancer.
I depend on an FM transmitter to make my computer's sound (mostly talk podcasts but also occasionally music) available in the various places where I work, where the "client" device is a just a simple FM radio, the kind that can be bought at a yardsale for a dollar. I could use an MP3 player, but FM radios burn through batteries much more slowly and it's an added hassle to transfer MP3s from a computer to a device, where it's also harder to arrange the order of a playlist. Furthermore, my MP3 players cannot drive speakers, whereas a simple clock radio has an adequate speaker for playing a podcast (and it's nice to be able to work without headphones.) The main disadvantage of an FM radio as a digital music client is the lack of interactivity, but that's not much of a problem when your hands are covered with tar, mud, or concrete. When I have a job to do down at the greenhouse or in the basement, I queue up some podcasts in my XMP player on Woodchuck, gather up my tools, and head off, glancing at the red LED to make sure the FM transmitter is on (it's been flaky lately and sometimes it's off because I've been watching porn, the soundtrack of which I wouldn't want the neighbors to stumble into accidentally).
But as I said, my FM transmitter has been flaky lately. It's a kit I built nearly six years ago, and for some reason it dies every now and then and doesn't revive until I flex its printed circuit board. So I'd given up on it and started using an MP3 player and headphones, though I'd ordered a replacement transmitter (costing $55) from a Hong Kong-based seller on Ebay. Today it arrived, and, after building a 12th wave matching transformer to send its 50 ohm RF output up my 75 ohm antenna cable, I powered it up.
The old transmitter had a broadcast power measured in the milliwatts, but this new one is a five watt powerhouse. Its metal chassis actually gets warm when it's operating, as did the 75 ohm-to-300 ohm balun at the antenna (until I replaced it with a balun having thicker windings). I was eager to test the range of the new transmitter, so I went for a walk down the farm road with my cheap Walkman-style FM radio. After hiking nearly a half mile, the signal (coming from a omnidirectional dipole) had never broken up. This caused me to worry that perhaps my transmitter would draw the attention of the dwindling population of FM radio listeners (and ultimately the FCC). So back at the house, I redirected the signal up to the multielement yagi antenna on the roof, pointed roughly down the Stick Trail (and away from the pockets of civilization most likely to alert the authorities). Then I went for a moss-gathering walk down the Stick Trail. At about three quarters of a mile down the trail, the signal began to break up intolerably, which led me to think that either I was out of the yagi's crosshairs or that it was experiencing a transmission mismatch with the transmitter. Still, the signal was proving much more powerful than what I'd gotten from the old transmitter, and it was opening up all kinds of possibilities. With the superior reception of my car's stereo (and after some tinkering with the antenna), I might be able to receive broadcasts miles from home. I think, however, that I will be careful to turn off the transmitter when I'm not using it. It's a powerful device and with power comes responsibility and paranoia (just ask your neighborhood gun nut).
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