Strike Up the Bandwidth

On a recent Friday night, our neighbor returned from a stint working out of town. He awoke on Saturday all set to catch his favorite radio show--"Car Talk"--on the public station. It wasn't there. At its usual spot on the dial was a garble of country-western music. Thus did he meet what the whole neighborhood now calls the Static of the Spheres. The band snatchers have invaded our hilltop, and the public radio station is heard no more.

That's a fancy way of saying our hill has one more radio transmitter working in the local antenna farm, and a harmonic radio frequency of the new station--combined with that of another station--make, in effect, an electromagnetic echo which drowns out the old favorite. This has provided significant learning experiences for those of us living near the new transmitter. We've learned especially that regulations aren't quite up to the complications technology can create. That is, we've learned we're in deep trouble--or at least our listening habits are.

It could be worse. Consider the plight of radioastronomers, people who study the phenomena and processes of the universe by means of the radio-frequency portion of the electromagnetic spectrum. To them, band snatchers are a serious professional threat, because whole classes of information can be lost if certain radio frequencies aren't clear. Some of those frequencies have other uses--and users.

Motorola Communications Inc. is one such user. Motorola has big plans for a cellular telephone network that will serve remote areas not now accessible to these systems. The network will be based on an array of 77 satellites. Motorola sought Federal Communications Commission approval to operate its satellite transmissions at frequencies ranging from 1610 to 1626.5 megahertz (million cycles per second).

Those frequencies happen to blanket one of the four bandwidths (1610.6 to 1613.8 MHz) on which radioastronomers can detect the radio waves emitted by hydroxyl radicals---electrically charged molecules with one atom of hydrogen and one of oxygen. The signals of hydroxyl radicals indicate the presence of these two important elements, which is keenly interesting to astronomers, and can indicate developments in the formation of stars.

According to Science magazine, the FCC is set to give Motorola exclusive use of this frequency band. Even though the radioastronomers have no legal leverage in the matter, Motorola has been willing to talk with representatives of the National Radio Astronomy Observatory and the National Science Foundation on finding ways to accommodate both communications and observations. By switching the satellites away from the hydroxyl frequency when they come within range of a radioastronomy antenna, Motorola intends to keep the skies safe for some kinds of research.

But not all. Another recent user of frequency bands needed by radioastronomers is the U.S. Customs Service. During the last few years, Customs has emplaced six tethered helium-filled blimps around the southern edge of the nation. The blimps are a kind of poor man's satellite; they hover at 10,000 feet, electronically watching for small planes trying to sneak contraband across the border. The blimps' radar sensors transmit radio waves in the 1215 to 1350 MHz range---the band in which radioastronomers hunt for the spectral signature of hydrogen emitted by distant galaxies.

So far, compromise has been possible here too. One blimp is posted within range of the astronomical observatory at Kitt Peak, Arizona. Customs Service officials have agreed to turn off the blimp's radar when it would be pointing toward the peak---unless it is actively tracking an airplane at the time.

The radioastronomers know they're fighting a holding action, just trying to keep a few prime research frequencies against the ever-growing demand for the whole radiowave spectrum. Someday, it'll happen to them, too: they'll tune to their favorite star and get country-western music instead.