This time on the EC we'll go back to FM propagation and why are those towers are so tall? In short, it's because FM operates in the VHF - very high frequency - band, from 88 to 108 MHz. The VHF band works primarily via line of sight propagation. That means you need to "see" the transmitting antenna in order to receive the signal. If something gets in the way be it trees, a hill, buildings, etc it can block the signal. Therefore, a nice tall tower has enough height to "see" over local terrain and hills. That's also why an exterior antenna, like on the roof of your house, or a car antenna, usually works better than antennas indoors.
By way of analogy, think of an FM transmitter as a big lightbulb on top of a pole. The taller that lightbulb is, the easier it is to see that lightbulb from wherever you are. The lower it is, the more likely it is that a hill or a house or a tree might block your view.
Providence, RI – This week on the Engineer's Corner we talk SOLAR OUTAGES. I know, it sounds like the next (terrible) Michael Bay movie but it's really far more benign.
It has to do with our satellite downlink from NPR. We have a hefty 13-foot-diameter satellite dish, located in North Providence; there's no room for it at One Union Station! It points to "Galaxy 16," a telecommunications satellite in "geostationary" orbit that all NPR stations use.
A common tech support request I get is for help with our stream/webcast from our listeners. The "digital illuminati" often like to claim that the web will mean the death of radio any day now, but streaming is still decidedly more complex and more tricky than radio's "push button, turn knob, get programming" simplicity.
Providence, RI – This is a test. This is a test of the Emergency Engineer's Corner. It is only a test.
Those iconic words, coupled with the tell-tale "brraaaaap... brraaaaap...brraaaaap" data tones, are widely known as the EMERGENCY ALERT SYSTEM, or EAS. Like its predecessors the Emergency Broadcast System and CONELRAD (CONtrol of ELectromagnetic RADiation), EAS is - at its core - a means by which the US Government can disseminate emergency information to the public at large in a short amount of time.
Providence, RI – This time on the Engineer's Corner let's talk about CODECS. Short for "encoder / decoder," codecs are a fact of modern life; used in cellphones, digital cable TV, digital television, the internet, you name it! Anywhere there's data, there's probably a codec involved.
A somewhat radio-related topic this time on the Engineer's Corner: Atomic Clocks! At NPR stations, like Rhode Island Public Radio, we rely on precision timekeeping because we coordinate our local programming with NPR's national programming via each end paying attention to a very specific clock. Everything is timed down to the second and, in some cases, to half-seconds! We use a special clock system from ESE to synchronize all our clocks in the studios. Such systems are expensive, costing thousands of dollars, because of their very high precision. But at home you can get pretty close by using an "atomic clock", available at most Radio Shacks, Walmarts and other, similar stores.
Welcome to the Engineer's Corner and since it's high summer I thought we'd talk a bit about TROPOSPHERIC DUCTING, an interesting and unpredictable phenomena that happens when it gets hot out, say, the mid 80's and hotter. When an FM or TV signal goes out into the upper atmosphere, if it encounters air that is warmer, instead of cooler, the higher "refractive index" can cause the signal to be bent. If conditions are right, it can be repeatedly "bent" into a "tunnel" or "duct" and carried for hundreds, if not thousands, of miles.