[BC] Diplexing AM Stations

[richardbrianjohnson at verizon.net]

 As others have noted, the spacing is very close. In general, it is possible to diplex any two transmitters at any frequency-spacing, including zero, into a common load. However, the most common MW diplexers use filters to reject the "other" transmitter. These are usually parallel-tuned circuits, often followed with a series-tuned circuit as well. The closer the frequencies, the higher the operating Q of the the tuned circuits must be. Eventually, you have problems with high-frequency modulation sidebands interfering __plus__ AF distortion of both transmitters because the load impedance changes within the sideband bandwidth.

My seat-of-the-pants says don't even bother designing such a device of the "filterplexer" type. That said, a bridge diplexer can diplex anything with "perfect" isolation but you lose half of your power in a reject load  --not good because program-modulated RF is the most expensive power available! .
 
 Cheers,
Richard B. Johnson
http://www.AbominableFirebug.com
 
On 07/01/14, Dave Dybas (dd92251*aol.com.INVALID)
oldradio.com>
 wrote:
 
The best person to ask is Kurt Gorman of Phasetek.... he has diplexed closely spaced stations previously with some specially designed filters that give great rejection.