Sunday, June 7 2009
My new five watt FM transmitter has made it possible for me to listen to my computer reliably throughout the house as well as a considerable distance into the forest, although finding a proper antenna that will allow the transmitter to run without overheating (that is, without developing an excessive standing wave ratio) has been a struggle. So today I decided to build a whole new antenna for it. I'd found some designs on the web for a so-called J-pole antenna, and yesterday I'd bought a ten foot stick of half inch copper pipe with which to build the two elements of the antenna. Sizing the elements properly for the transmission frequency is critical, so for this I relied on a J-pole calculator, and I did most of the measurements using the metric scale, which works best when calculators are producing decimal fractions. I'm handy with soldering copper pipe, and it didn't take long for me to assemble the antenna (which ended up being more than eight feet tall). As recommended by several websites, I didn't solder my coax cable connections to the antenna but instead clipped them on (I actually used copper mounting brackets, which can be bent to fit snugly over half-inch copper pipe). This would allow me to move the feed location up and down to find a perfect match for my particular setup. I come from the world of digital DC electronics, and everything about antenna electronics seems counterintuitive. For example, the entire antenna I was building seemed like it should have been one contiguous grounded piece of copper, but in the high-frequency world of FM radio, a lump of grounded metal can have several electrical nodes on it, and these can be at a very different potential from other nearby places on that same piece of copper. Finding these nodes and attaching to them is what makes the difference between a cool-running high-output transmitter and one that heats the laboratory without actually producing much of a signal.
I've had an SWR meter for years (since my initial FM transmission attempts six years ago), though I'd never actually figured out how to use it and it never really mattered (since the power of my transmissions had been so low). Today, though, I wanted to tweak my new J-pole antenna to properly match it to my transmitter. Unfortunately, though, I didn't have the CB-radio-style PL-259 plugs compatible with my SWR meter, so I had to improvise using clips and all the usual problematic techniques for matching incompatible hardware. The SWRs I measured this way were frighteningly high, and, judging from the heat given off by my transmitter, they must have been somewhat valid. So I had to abandon my beautiful copper J-pole antenna for the time being.
One of the least pleasant things about building structures is the constant disturbance it causes tiny creatures. I'm a sucker for little harmless beasts just trying to live their lives in peace. I try to work around paper wasps, I rescue drying earthworms and drowning beetles, and I move salamanders and slugs from the path if it seems likely I'll be walking that way again. But some forms of disturbance are inevitable, particularly when building things from natural materials gathered nearby. This is particularly true of stone walls and pathways. Lots of things live underneath stones. I'm always a little sad to tear off the roof of an ant colony, sending the members exploding outwards in a futile effort to defend the nest (and viciously attacking other similarly-bewildered animals with whom they'd previously been living peacefully). Less often I find salamanders, though I assume they can easily find new places to live. Even less often I encounter snakes, and these are invariably small garter snakes. In the process of moving large rocks from off these creatures, I'm surprised that they are almost never crushed. Today, though, when I was upending an enormous three hundred pound slab of bluestone, it proved too heavy and I let it slam down. When I finally was able to get it out of the way, I saw that I'd crushed a garter snake about midway down his length. He was paralyzed beyond that point and was moving about pathetically. It was terrible. So I put him out of his mercy, hacking him apart with a mattock. I still haven't gotten over how terrible this made me feel. As for the rock, I was able to move it about fifteen feet along the contour of the slope to the greenhouse path, where it became the top step in a landing. Eventually another garter snake will surely take up residence beneath it, unaware of the victim it claimed today.
None of our household televisions are modern enough to be able to receive over-the-air digital broadcasts, but I have one of those set-top boxes for receiving and decoding such signals. Since we receive all of our broadcast television programming through a satellite receiver attached to a Tivo, I was only experimenting with the set-top box out of curiosity. What channels would I be able to receive? How clear is digital television? I was also curious about what parts of the radio broadcast spectrum were being abandoned in the transition on June 12th, though this was the sort of thing I would have to research online.
I have a large yagi (fishbone-style) antenna above the solar deck, and it (along with a WiFi dish) are on an antenna rotator. I can point it in any direction on the compass, and, since our house is on the edge of an east-facing escarpment some 450 feet above the Esopus Valley, we generally have good radio reception of all kinds (most broadcast antennæ in our area lie in an arc stretching from Albany to the north, Connecticut to the east, and New York City to the south). In the bad old analog days I was able to get about 12 television stations with my antenna. Today when I was experimenting with the digital set-top box, the auto-scanner only managed to find three or four digital broadcasters throughout the compass, and those tended to be no further away than Poughkeepsie. One of those broadcasters was broadcasting four separate channels, though all of them were religious in nature. So much technological progress, but in the end all it ends up providing is a conduit for an unhelpfully medieval world view from a time when everything was explained by magic and miracles.
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