Discussion in 'Amplitude Modulation' started by K5UJ, May 30, 2018.
As long as the frequency separations are > = 100 kHz, it is a straight forward task.
Most BC antennas today are 0.222 Wavelength to 0.3 Wavelength (Lambda) in height with "T" type AnTenna Matching Units (ATU's), but they don't all have to be the same Wavelength in a Multi-Tower array.
Below is a Diplexer for two stations transmitting into one antenna.
The four stations are:
WXYG (540 kHz) - 850W/250W, WBHR (660 kHz) - 10kW/500W, WVAL (800 kHz) - 850W/250W, and WMIN (1010) - 1700W/240W into a 7 tower system.
It appears all of the towers are 270 ft. tall and range from 0.18 wavelength to 0.3 wavenlength in height.
The antenna, transmission line and matching network all work together as components of a resonant system. Walt W2DU(SK) wrote extensively on this topic in his conjugate match treatise.
Actually it's more like 15 feet. The WGN tower is the same construction but a bit taller. Both towers went up around the time of WW2.
I think Dave's point was that a lot of operators don't know what resonance is and what matters is efficient transfer of power from the feedline to the antenna.
Mark Persons is a good guy. Sorry to see him exit the business because he had a lot of good stuff for sale but I'm happy for his being able to retire and take it easy.
A 250 w. station down at the low end of the band is about like a 5 KW station up at the top of the band in terms of ground wave reach.
I wish Groth were still around provided they still used metal parts instead of cheap crappy plastic like a lot of turns counters today.
We have a 5kW station on 540kHz than has better coverage than does our 50kW station on 1540 kHz.
If I were going to own a property, I'd probably go with the high dial spot 50KW because you can have a smaller tract of land, 90 degree towers that don't need painting and lamping, can even be free standing, and you the electric bill isn't too bad with a 90% efficiency rig running some sort of modulation dependent carrier scheme. You cover your COL okay also. Also storm QRN isn't quite so bad up near 1600.
It's interesting that the old border blasters were up around 1500 but you have to remember they didn't care about groundwave anywhere near as much as skywave.
WBBM Itasca RIP:
The aux tower was brought down yesterday with the help of a backhoe. Today, eyewitness reports the main 190 degree tower was felled at 11:30 a.m. local time. She keeled over and laid out flat on the ground.
Gee, I drove past there just this morning. But way before the tower went down.
I'm surprised they did it today, given the bad weather this morning.
Also, I've always noticed how many transmitter buildings are exactly of the same construction.
Could someone give some info on who designed these and how they got to be the standard?