[AMRadio] AM Power

[Paul Christensen]

> Jim, I think there was a misunderstading about the DX50; it does 50 KW
> dead carrier; maybe that was what was meant by "100%" output, i.e.
> maxumum carrier power (actually it has some reserve).

We installed a Harris DX-50 at the legendary WAPE-AM daytime site back in 
1995 -- My last project in the dreadful broadcasting industry.

Part of our acceptance testing from Harris was the ability to easily attain 
150% positive modulation, reference 100% negative at 50KW carrier.  It 
passed the test as well as the other demanding acceptance test of modulating 
the DX-50 with a 50 Hz square wave.  It easily passed square-wave testing 
with nearly zero tilt.  However, as I recall, total current shot up to 
hundreds of amps.  We kept it there for 30 seconds before claiming 
"acceptance."

The DX-50 replaced an aging Continental 317C1, later modified to a C2.  But 
the Continental's predecessor at WAPE was the Brennan "composite" 
transmitter -- a homebrewed design by WAPE's original owner, Bill Brennan 
and built by brother Cyrus Brennan.  The transmitter design was put through 
scrutiny as part of Bill Brennan's master's degree thesis at Harvard.

http://www.oldradio.com/archives/stations/ccs/wokvpix.htm
http://en.wikipedia.org/wiki/WAPE_(defunct)

The final design was a novel adaptation on a James Weldon-modified Doherty. 
Positive modulation?  I personally witnessed over 180% positive modulation 
at 50KW carrier.  The amount of power supply and RF component reserve for 
that homebrew transmitter was extraordinary.  Peak and Carrier tubes were 
water-cooled Machlett's.  The heat exchanger?  A swimming pool that emerged 
up into the studio.  In later years, the pool was filled-in owing to some 
obvious liability issues and a "wading pool" was constructed as the new heat 
exchanger.  A similar unit was also designed for the six-tower night-time 
site at Orange Park, Florida.

Paul, W9AC