[Amps] Modern AM Broadcast Transmitters

[Jim Brown]

On Sun,12/18/2016 8:04 AM, donroden at hiwaay.net wrote:
>  WLW was licensed for 500KW ( 1/2 Megawatts ).

As a senior EE student at UC around 1963-4, I had a tour of WLW and the 
VOA site. That 500kW rig was still there and was fired upfor us, running 
into a dummy load (cooled by water circulated from a fountain out 
front). As I remember the story more than 50 years later, that was never 
their primary rig, although I think it was intended to be, and did get 
on the air for some overnight testing, but WWII happened, and they 
stayed at 50kW. The modulation transformer for that big rig "sang" like 
a big loudspeaker!

I had worked for a broadcast consultant for a year a year earlier, and 
the office had a map book of all the antenna contours for every 
frequency on the AM band. WLW was one of two clear channel stations that 
had no other allocation on their frequency in the US. I think the other 
was WOAI, on 1200 kHz in TX.

That VOA station was a wonderful engineering tour -- I had just finished 
my course in Transmission Lines, so it was like a "lab" for that course. 
I'd been a ham since 1955, so I really appreciated the antenna farm too. 
As I recall, the VOA rigs were 20 kW, and antenna gains were in the 
range of 20dB for the rhombics and a bit less for the two curtains. They 
picked up a dB or two by replacing the termination resistance with a 
transmission that they fed back to the antenna input in phase with the 
drive from the transmitter.

73, Jim K9YC