[Amps] Modern AM Broadcast Transmitters

[donroden at hiwaay.net]

Quoting Donald Fox via Amps <amps at contesting.com>:

> Gents:
> So, if WLW ran the "old school" way of modulation, and had at one  
> time an actual 500 KW carrier, would their meters have stood at 500  
> kw steady, or hung around 125 KW with 0 modulation and then swung up  
> to 500 from there?


Great Question.

  WLW was licensed for 500KW ( 1/2 Megawatts ).  Their *Peak* power  
would have been 2 Megawatts at 100% modulation.   With a steady state  
audio tone, again at 100% modulation, the positive peaks would be  
offset by the negative peaks on a slow-to-respond meter and the  
average power would have shown 500KW and the slow meter would have  
indicated no movement up or down from carrier power.

   BUT........ looking at the carrier with a fast acting oscilloscope  
would show a voltage increase from carrier levels to 2 x carrier level.

Twice the voltage into the same resistance ( antenna ) = twice the current

voltage doubled times current doubled = 4 times power. ( peak )  2 Megawatts

Current ham transmitters capable of 100 watts peak SSB can work on AM   
by insuring that your carrier ( no modulation ) doesn't exceed 25 watts.
Keep the mike audio at or below ALC threshold and you should have a  
clean AM signal.

Don W4DNR

DonR