Nifty antenna tackles problems of FM reception

First of two parts

It was a dark and stormy night - not really, it was actually agray and rainy day - when the doorbell rang. The button pusher wasmy friendly United Parcel Service delivery person. After the usual"sign on line 18" routine, I was handed a rain-speckled, brownpaper-wrapped package.

It was small and weighed just a few ounces. I held it to my earand gave it a shake to help me guess its contents. When I tossed itonto the desk, it immediately got the once-over by Clawed, myofficial package inspector. He quickly decided it contained noproduct of interest to an Abyssinian yet stuck around just to besure. Perhaps he thought it held some of those white plastic"peanuts" he enjoys batting around so much.

One of the great parts of my job is what I refer to as"spontaneous Christmas," the unexpected arrival of a piece of homeentertainment equipment for evaluation and testing. That day's"gift" was a powered indoor FM antenna, model "pi2," from TerkTechnologies. While some products I receive are quickly repacked forreturn after a brief "play with it" period, the Terk pi2 is now animportant part of my home entertainment system. I guess when theevaluation period is over, I'll have to fork over some cash to keepit - and I'll do it gladly.

You see, I live in very hilly San Francisco. Our wonderful,famous-around-the-world bumps in the earth play havoc with FM and TVreception.

The problem is twofold. First, FM signal propagation is prettymuch line-of-sight. Unfortunately, I live at the north end of thecity, while many of the FM-transmitting antennae are set on a singletower near the center of the city, and many more are on a mountain atthe far south end. Both areas are separated from me by a series ofpicturesque hills. Still other broadcasting antennae are moredistant, at all points of the compass, with numerous hills inbetween. Second, even if my flat were atop one of our hills, in fullview of some transmitting towers, I might still suffer the insults ofa condition known as multipath.

Multipath is a fancy name for bounced signals. Picture in yourmind a transmitting tower, with radio frequencies radiating from itin all directions. A part of the signal goes directly to my place,while other parts head out in all directions. Some of those "other"signals strike hills, bridges and tall buildings, and after bouncingaround like a ball on a billiard table, eventually find their way tomy FM tuner.

The problem is, although radio frequencies travel at lightspeed, the bounced signals arrive a few milliseconds after the directsignal. The result is lots of distortion; on a TV set we see thisphenomenon as "ghosts."

Stay tuned for better reception.