Bear Flag Republic Radio Weblog

< 7:02:42 PM        >

When I moved to Palo Alto in 1985, my landlord was a scientist at a large defense contractor. He specialized in antennas, especially those of the sort put on satellites nobody's allowed to talk about. But he was bored with the science, he told me. "Antenna theory is done. Now it's all about implementation."

Apparently not. Here comes Rob Vincent, age 60, of Rhode Island. He's designing antennas one ninth to one third the size of normal full-size antennas, with 80%-100% of the efficiency.

See links here, here and in the New York Times. (Thanks to Buzz for the pointer.)

None of the articles and posts I've seen so far address the biggest potential benefit in the short term: reducing the huge amount of air space and real estate required for AM radio transmission.

Conventional (in fact, regulatory) wisdom holds that signals on AM are shaped almost entirely by their electrical length. Half-wave to 5/8-wave antennas are considered most efficient. A half-wave antenna at the bottom end of the AM band (540KHz) would be nearly 900 feet high. At the top end of the band (1710KHz) it's around 140 feet. That's why, on AM, whole towers radiate. Most also have directional arrays involving multiple towers. All are required to have ground systems in which copper straps are buried for hundreds of feet in all directions from the towers. That takes up a lot of room.

In decades past, when land was cheap and nobody made environmental impact statements or cared about migrating birds, putting up an AM transmitter wasn't a huge deal. Now it is. I think Mr. Vincent's solution might allow lots of AM stations to "build down" their enormous size, or to relocate to better places.

I might be wrong, but that's what makes sense to me after reading this story so far.

comments < 6:59:15 PM        >