Posted by mesomewierdo Directional AM antennae are often found in a phased array-- that is, several identical ones in a geometric pattern... like a precise line. Also AM antennae are usually stuck in a swamp... the ground conductivity helps. If "you're going to do it anyway" consider most AM licenses are for 1/10 the power at night. That FCC database above lists GPS coordinates so research should be easy. Consider ancillary services (cell phones, pagers, religious low power Tv stations, microwave repeaters) that lease antenna space from the main broadcaster. ...
|
Good information. In the USA, the highest FCC-allowable MW (AM) signal power is 50000 watts. Ten percent of 50000 watts (the highest AM broadcast transmitting power licensable) is still 5000 watts, and still enough to cook you like a hot dog in a microwave. Even if you live, RF burns, even from just a few hundred watts, are really nasty things, with different frequencies causing different physical or neurological effects. In most of Europe, the limit is either 50000, 150000, or 500000 watts, depending on country. In Mexico, the limit is now 250000 watts. There's often a lightning arrestor connecting the Mast Radiator to ground with a very high resistance. Don't look at that and think that despite the huge insulator, the tower is grounded. Look closely at the mast's guys (the tensioned wires that support it), you will see insulators there too, usually right near the top, but I have seen them right near the bottom. If they are near the bottom, the guy should be considered electrified, too. Mast radiators never have any sort of microwave dishes or other smaller antenna gear attached to them. Not all mast radiators have their own helix buildings. Depending on the length, not all require inductance tuning, and some may share tuning equipment. NEVER ENTER A HELIX BUILDING! NEVER EVER ENTER A HELIX BUILDING! NEVER EVER, EVER, ENTER A HELIX BUILDING! If someone's chasing you with a gun, NEVER ENTER A HELIX BUILDING! Helix buildings (the little squarish huts often found immediately next to a mast radiator) have nothing inside to see, will have no lighting at all, and are extremely dangerous to enter while the transmitter has power. Transmitter or antenna technicians don't even enter them with power on, there is no available safety equipment. Don't even touch the outside of the building at a high powered transmitter site. Longwave masts almost always have these buildings, Midwave (AM Broadcast) masts do about 60% of the time, though in probably half of cases, there is not one for each mast, they are either paired (one per two masts) or there is just one. Longwave transmitters may be in excess of one million watts, though are more typically from 200000 to 750000. The longwave broadcast band is not commercially licensed in the United States, but transmitters of the same frequency and technology (essentially AM) are still around here and there for other purposes (LORAN-C for one). For those in the USA, the FCC has a list which is searchable by map coordinates, tower height, tower type, city, street(s), address, broadcast type, and lots of other ways. It will tell you exactly what is on the tower, what frequencies are licensed, what power is licensed, who owns it, how it is supported, how high it is, and a lot more. It is freely and anonymously accessible to the general public. Old AT&T Long Lines TD-2 towers are safe to climb up, as long as they aren't used for anything else. Many are simply not in use, many are leased to cellular and radio companies. They are very distinct with their large 2500MHz horns on top, and quite interesting to look at. Unused sites come up for auction periodically, especially the ones AT&T still owns. You can buy them fairly inexpensively, building and all, often for as little as $30-50000 in many cases. The entire AT&T long distance microwave repeater system is shut down, the last segments as of 2002.
|