On 12/18/2018 11:54 AM, Fred Jensen wrote:
Indeed. AM broadcast vertical antennas are rarely 90 or 180 degrees, especially if they are a Class A station. I think both KFI and KNX in Los Angeles have 195 deg verticals. The design goal is to maximize field strength in the service area, accomplished by adjusting the height of the current maxima in the antenna element.
Exactly right. Although I've never done the design work for them, I suspect that bandwidth can be increased by careful design of the matching networks.
Technical details of US broadcast antenna systems can be queried from this link.
https://www.fcc.gov/media/radio/am-query
All resonance means is that the reactive component of the impedance at the feed point is zero. A bigger problem for stations at the low end of the band ... KFI is at 640 KHz ... is that the usable bandwidth of the antenna can be less than the bandwidth of the DSB signal.
And it's an even bigger problem for stations using directional arrays! Those arrays are required by the terms of their license to protect other stations on the same or adjacent channels from interference. As a college student, I worked for one of those stations, and later for a consultant (Pete Johnson) who designed those arrays. Pete and Carl Smith wrote the technical sections of FCC Regs for AM BC after WWII.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
