We've talked in the past about skywave propagation, but it's cool when you heard about real-world examples of it. Recently I've gotten several emails from "DX'ers" (Distant Reception enthusiasts) in Europe saying they've been able to hear Latino Public Radio on 1290AM all the way across the Atlantic!
We have put a temporary setup in place with a donated 30 watt transmitter on loan (with the antenna array's gain factor of 2.1, it's really more like 63 watts of Effective Radiated Power), and a special radio that's tuned to 102.7FM (there's a high-gain FM antenna on the rooftop tower) and puts out the composite signal directly into the new transmitter. This effectively makes 91.5 into a "repeater" of 102.7FM.
When you’re a broadcast engineer, you get used to receiving calls at odd hours proclaiming things that tend to fall outside the bounds of “normal.” It’s just the nature of the job. But even your intrepid engineer can be surprised sometimes. Friday morning, August 23rd, was one of those times.
That morning I got a call informing me that WCVY, our 91.5FM signal for much of Kent County, was off the air.
Air conditioning. Cool heaven for those who have it, blazing hell for those who don't. It didn't used to be terribly common in broadcast engineering, but it's become moreso in the last ten years. The reason is that, more and more, audio processors, RDS encoders, audio encoders/decoders, studio/transmitter links, remote control systems, and even the transmitters themselves, have all become increasingly "computer-like" with IC's, hard disk drives, power supplies, electrolytic capacitors and the like. All things that fail quickly when operated in temperatures above 80 or so, and the warmer it gets, the faster they fail!
Most people have heard of the "Three Mile Island" nuclear power plant accident of 1979. But it's famous among engineers for being a "normal accident", in that there wasn't any one thing that nearly caused a meltdown of catastrophic proportions...it was a series of little things inside a highly complex system that all happened as part of "normal" operations. None of which, by themselves, was terribly problematic. But they all happened at once, and that was a problem.
BOO! This time on the Engineer’s Corner, we’ll talk about PHANTOM POWER. Usually not as ghoulish as one might expect, phantom power has to do with microphones. Specifically, some microphones have active circuitry inside them. That means they need power to operate, but it’s unwieldy to run a separate power cord and audio microphone cable. So a phantom circuit is used to provide DC power on the same three wires (positive/hot, negative/cold, and ground) out to the microphone that the audio from the mic also uses.
A phantom circuit is one of those nifty things in electronics that looks, to the layman, like it can’t possibly work...but it does anyway.