AM Tower Sharing

[trusty]

OK - another dumb question to satisfy my curiosity:
When two AM stations share the same tower (such as WCBS/WFAN), are there two separate lines going up the tower cut to different wavelengths, or do they work off the same line (Is this "diplexing"?)?

Thanx again. (Now I can sleep.)

 

[stormy01]

See if this article helps to answer your question, it does talk about WFAN/WCBS, which you mentioned:
http://radiomagonline.com/transmission/radio_diplexing_am_transmitters/

 

[tanner]

540 and 740 in Orlando also

 

[davideduardo]

OK - another dumb question to satisfy my curiosity:
When two AM stations share the same tower (such as WCBS/WFAN), are there two separate lines going up the tower cut to different wavelengths, or do they work off the same line (Is this "diplexing"?)?

Thanx again. (Now I can sleep.)

Each transmitter feeds coax to a diplexer which is both an antenna tuning unit for each station and a rejection network for the other station. In other words, if we have two stations on 570 and 810 the trnasmitters both go into a box at the antenna base. 570's section keeps 810 from going backwards into the 570 transmitter and matches the 570 freqency to the tower. The 810 input keeps 570 out of the 810 transmitter and matches 810 to the tower.

The coax can pretty much be of any reasonble length... it is not tuned. Tx output is generally 50 or 52 ohms and the ATU matches the coax to the tower, which can be in wide range of impedences, and with +j or -j reactive components.