KNBC's New Franklin Antenna, 1949
KNBC (KPO)'s present 550 ft. tower was completed in 1949. This type of antenna is called a Franklin antenna, a design used by only a few AM stations in the U.S. The antenna is easily recognized by the porcelain insulator in the middle of the structure. A traditional Franklin antenna consists of two half wave antennas stacked end-to-end and fed in phase. At 680 kc, this would require a tower 1,500 ft. tall, an obvious impracticality. The KNBC tower measures 400 ft. to the midpoint insulator. The upper portion of the tower is shortened to only 150 ft., and this is compensated for by a 50 ft. diameter capacitive top loading "hat" at the top of the structure. The top section is fed from a shunt tap on the lower section. There is a copper tube that runs up from the tap on insulated stand-offs, where it connects to the upper section just above the insulator. The Franklin Antenna is used as a means to lower the radiation angle of the signal. This increases the ground wave coverage of the station, and reduces the night time interference at the fringes of the ground wave signal, caused by sky wave signals originating from the same tower.
In the photo at left, the old east tower is visible in the background, with the
KNBC-FM antenna on top. [Go to Index of Articles] [Return to Photo Archive] [Return to Home Page] |
|
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.
|
