This week, we surf to Web sites that provide valuable, on-line tools for Amateur Radio applications.

If you're a repeater operator, have an APRS base station, or are just curious about the potential performance of your antenna system with respect to the lay of the land, you can calculate your antenna's height above average terrain (HAAT).

HAAT is not the same as your antenna's height above sea level (ASL). HAAT is the height of your station's antenna as it relates to the average height of the terrain in a specified radius (typically 10 miles) surrounding your antenna. For example, if your antenna is 1500 feet ASL and the average height of the terrain in the 10-mile radius surrounding the antenna is 1400 feet, your antenna's HAAT is 100 feet.

In the good old days (like last week), you calculated your HAAT by using topographical maps and recording the height of the terrain in 2-mile increments along the eight compass directions (N, NE, E, SE, S, SW, W, NW) radiating 10 miles out from your antenna. This gives you 40 readings, which you add together and divide by 40 to obtain the average height of the terrain in the measured 10-mile radius. Subtract this figure from the height of your antenna ASL and the difference is your HAAT.

Calculate your antenna's Height Above Average Terrain (HAAT) at the FCC's Mass Media Bureau, Audio Services Division's HAAT page.

Life is much easier in the 21^st Century! The Audio Services Division of the Federal Communications Commission's Mass Media Bureau has a Web page [Antenna Height Above Average Terrain (HAAT) Using GLOBE Terrain Data page that simplifies the process and likely results in a more accurate HAAT. For what it's worth, my calculation and the FCC's calculation of the HAAT of my APRS digipeater differed by 21 feet (my 481 vs. the FCC's 502 feet).

All you need is your exact latitude and longitude (down to degrees, minutes, and seconds) and the height of your antenna. Enter that information at the Web page and the results appear almost instantaneously. This page was set up for calculating the HAAT of TV and FM broadcast stations, but there is no reason why hams can't use it, too. (Thanks to Dave Flack, W6DLF, for clueing me into this page.)

The only drawback is that the antenna height and the HAAT are inputted and outputted, respectively, in meters. To work around this dilemma, I recommend surfing to Poseidon Software and Invention's Metric and English Conversion Utility page, where you can convert from feet to meters and meters to feet quickly.

Until next time, keep on surfin'.

Editor's note: Stan Horzepa, WA1LOU, of downtown Wolcott, Connecticut, is an ARRL Life Member and an incessant contributor to QST and QEX (504 pieces in 22 years), not to mention the author of five ARRL books and contributor to a bevy of other ARRL titles. First licensed in 1969 as WN1LOU, he upgraded to WA1LOU in 1971. Stan began using computers with Amateur Radio in 1978 when he bought a Radio Shack TRS-80 Model I computer and wrote BASIC programs to dupe contests and calculate antenna bearings. A virtual beach boy, Stan has been surfing the radio dials as long as he can remember, however, instead of surfing all over Manhattan and down Doheny Way, he now surfs the Internet searching for that perfect page. To contact Stan, send email to wa1lou@arrl.net.

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