This is the AM Antenna Section of
The Broadcast Archive

Maintained by:
Barry Mishkind - The Eclectic Engineer
 

AM transmission systems have three major goals:

    1. To cover the area of interest, with a signal that overcomes manmade RFI

    2. To put as much groundwave out as possible, avoiding "fading" at the fringes of coverage

    3. To reduce skywave interference to other stations on the same and adjacent frequencies.

Since the electrical height of a tower controls, to a large extent, the level of signal received at any given point, there is often a balance between #2 and #3.

 

Today, a regional channel often needs 50 kW to be heard above the noise floor, even locally.
In the 1960s, 5 kW, the Class III maximum, was good for a hundred miles or more, under conditions of ground ground conductivity.

Today, just about every appliance uses switching power supplies, or variable frequency three-phase motor drives. Lots of noise, and clothes washers or dryers do not have an FCC label on them, even though these appliances produce more AM band RFI than any personal computer.

Notice that a 225 degree radiator can produce 440 mV/m/kW at 1 km, but, the 225 degree radiator has exceptionally poor fading within the service contour. This is not important to a Class C, but an absolute killer for a Class A.

The Average for a US non-directional Class A station is 195 degrees.

 

 

Want to know more about Oldradio.com?  

Or, just need to get BACK TO THE MAIN PAGE?

Thanks for visiting ... I hope you find the site interesting!

Copyright 1993-2006, 2007  by Barry Mishkind. This material on this site should not be reproduced or reposted in whole or part without express approval.

It would be a kindness if you'd take a moment and let me know who you are and what interests you have. If you can share some information, or even a picture, that would be great! Just use the address below. Thanks. (Please note: Due to the huge amount of spam on the internet, it would be extremely helpful if you would use something like [Oldradio] in your subject line, so the filters don't get in the way.)

An important note about this resource:

We have used many sources, including FCC files, university lecturers, historical publications and more, and have tried to be as accurate as possible, not repeating many of the myths of the industry (such as the Uncle Don Story) nor histories "manufactured" by promotion departments. However, I am not perfect, and may well have overlooked something. If you do see an error or omission, please let me know.

The accuracy and expansion of this resource depend upon our SHARING our efforts.

  • If you can help, please share your materials or information.
  • Due to the huge amount of spam on the internet, please use something like [Oldradio] in your subject line. 

  • Thanks a megaWatt!
  • snailmail:

    Barry Mishkind
    2033 S. Augusta Place
    Tucson, Arizona 85710