Adman4120 said:
Scott...In the example you provided me about WRFD's antenna being lower than the WCBS antenna, thus, their skywave signal shoots out at a high angle, is this a standard? Meaning that the lower tower height of any radio station will have a better skywave angle?
I'm a journalist, not an engineer, so we're way out on the edge of my technical competency here...but having said that: the old "class I" clear channel stations - the WLSes and WBBMs and WHAMs of the world - had to meet minimum antenna-efficiency standards, and that pretty much dictated the use of tall towers, generally in the range of 190-200 electrical degrees. Those tall antennas tend to have fairly shallow skywave takeoff angles, which means their skywave lands farther from the transmitting antenna.
It was not unusual in the earliest days of vertical antennas to see stations modify their towers to alter the skywave takeoff angle. WSM and WLW both built towers in 1932 that were a little too tall, and both towers had to be shortened slightly to avoid creating skywave/groundwave interaction that cancelled out their signals in a ring about 75 miles out from the towers. For WLW, that meant problems with its signal in Columbus and Louisville and Lexington; for WSM, it wiped out Chattanooga and Huntsville.
The former "regional" stations tend to use shorter towers - 90 degrees is typical - though there are exceptions. WGMF 1500 in Watkins Glen had an exceptionally tall tower when it was built in 1968 to avoid sending skywave toward WTOP in Washington. The station later moved to 1490, and when the tall tower fell a year ago, it was replaced with a shorter one, there being no need for a tall tower to protect other "graveyard" stations on 1490.
Another question on the same subject of tower height is...In Chicago for example, I believe that the sports station on 670, WGN at 720, WBBM at 780 and WLS at 890 are all non-directional, 50,000 watt clear channel frequencies? Correct me if I'm wrong.
Does the tower height/skywave explanation apply? I guess my curiosity is that how come all 4 of those stations do not come in clear at the same time if they are all transmitting their signal from basically the same area and have the same power. Does that tower height apply and that is why I might get two of the station real clear, while the other two struggle. I always seems like WBBM at 780 and WLS at 890 boom in better than WGN and the station on 670.
It's very likely that when WBBM and WLS are coming in well, you're also getting plenty of signal from WGN and WSCR - but you're also getting adjacent-channel hash from the AM IBOC on WOR and WFAN.
WGN, WBBM and WSCR are all transmitting from roughly the same area west of Chicago; WLS is about 25 miles to the south, along I-80 in Tinley Park, and they all use antennas of roughly the same electrical height.
And one last thing I have always noticed. When the New York City stations and WBZ in Boston come in clear, the Chicago stations aren't even remotely coming in. And, when the Chicago stations boom in, the New York and Boston stations struggle to come in. Seems like the atmosphere favors one part of the country over the other, but never equal at the same time.
The ionosphere is a harsh mistress. There are all sorts of factors that can come into play, including auroral activity that can wipe out skywave from northern stations entirely. It's very hard to predict exactly how it will behave at any given time...which makes DXing all the more fun!
