FM range experiments
Friday, August 1 2003
Rain fell for much of the day in a prolonged drenching downpour. Though there'd been a lot of rain this spring, for the past couple weeks there has been very little precipitation and it came as a sort of subconscious relief. Another source of relief was the successful installation of a modem in the downhill neighbor's computer.
I continued experimenting with component replacements in my FM stereo transmitter. The setting for these experiments was, appropriately enough, my laboratory, where I had everything spread out on the floor, making and breaking test connections with a hot soldering iron. Periodically I'd take my old stereo radio out for a little walk in the surrounding woods to test the range. Unlike digital electronics (my usual interest), linear electronics are full of surprises. In any one experiment, there are so many variables that the scientific method soon gives way to black magic and cargo cult rituals. The myth of Cold Fusion has its origins in similarly sloppy science.
Nevertheless, I made a valiant attempt to allow the experiments to speak for themselves. After hours of tests I made a puzzling discovery: the lower the voltage on the collector of the NPN transistor used in the final RF stage, the greater the resulting range. I'd assumed the opposite would be the case, and had replaced the stock transistor with a hefty monitor color gun driver transistor, complete with heatsink, just so I could drive it at 12 volts. But I had much better range when I drove it at less than six volts.
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