Accessories

The locations we used were picked for their distance from the transmitter only. They were not pretested for good or bad reception or geographic diversity. However, because of the distance that was covered, we did move from inner-city high rises to low-lying suburbia. Also, thanks to the ice age, the Chicago metropolitan area is as flat as it gets. We didn't have more than a 100-foot elevation change through our entire test.

Your geographical location should be a determining factor in purchasing and mounting your antenna. We raised each antenna 20 feet above ground. ATSC recommends you place your DTV antenna 30 feet, but 20 feet was more practical for our test purposes—after all, we were already dangerously close to being the next mobile lightning rod.

At each of our checkpoints, all three antennas were mounted on a pole and oriented toward the transmitter for maximum reception. We used a spectrum analyzer to ensure a flat response over the 6-MHz channel spectrum. Our measurements were based on best overall reception and the shape of the receiving waveform, not merely on peak signal reception. Peak signal reception doesn't necessarily mean best tuner performance. This is why a field-strength meter is virtually useless in my opinion.

Tilt was measured to see how evenly the antennas worked over the 6-MHz channel spectrum. Of course, minimal tilt is desired because this means that we have a flat, square waveform on the spectrum, and it's easier for the DTV tuner's equalizer to correct and decode the signal. (We were looking for 4 dB or less of tilt.)

We used our analog TV for two purposes. The first was to look at the overall performance of analog TV versus digital TV. The second was to judge the amount of multipath transmissions and their relative strength. Multipath is created by the signal bouncing off of something before reaching your antenna. When this secondary signal is created, the bounced signal travels farther than the direct-path signal, so it arrives a little later at your antenna. Multipath manifests itself as ghosts in the analog picture.—JB