[AMRadio] League pulls RM-11306


Geoff/W5OMR ars.w5omr at gmail.com
Sun Apr 29 19:32:02 EDT 2007


Bill Smith wrote:
> There is plenty of reason to allow AM operation at 1000 watts carrier
> output.  Carrier serves to strongly reduce or eliminate background noise and
> provide a comfortable communications environment.  AM was severely
> short-changed by the 1500 watt PEP regulation.  AM stations are now
> restricted to only 350 watts carrier.

*IF* you're talking in a sine-wave, and have no distortion, your 
modulated signal is 4x the carrier.  So, for 1500w PEP, your carrier 
should be set to 375w.

Of course, we don't speak in sine-waves.  The human voice is a most 
complex range of frequencies, and if your speech equipment is properly 
setup, with attention paid to audio phase from the microphone to the 
modulator, with no /distortion/, I -guarantee- you will have better than 
100% modulation.  Meaning, your negative peaks hit the base line, your 
positive peaks will be beyond the 2:1 ratio of audio peaks to carrier 
base-line.

John/WA5BXO, Bacon and Don/K4KYV wrote a nice article on *asymmetrical 
audio*. Google for it.

Your 350w carrier might be being modulated beyond 100%.  if it's only 
100%, then it's at 1400w PEP.  If your SR is 3, then that's 3db more 
than 1400, or effectively 2.8kW PEP.  Mind you, the modulator has to 
have enough B+ on the plates of the tubes to produce the proper amount 
of audio to faithfully reproduce your voice, without distorting the 
audio peaks. 

John/BXO found out a long time ago, that in order to properly modulate 
his 1kW DC Input rig, he had to have (4) 813's in push-pull parallel to 
modulate a pair of 304TL's.  On the surface, you're saying 'holy jeeze, 
(4) 813's in a MODULATOR?" but that's what it took to have the audio 
equipment faithfully reproduce his peaked, nasally, east Texas Twang 
riddled voice.  And, man does that rig sound GOOD. 

John's biggest problem now is (other than finding time to get on the 
air, what with two boys in scouts, school activities, his wife, and 
running a successful business!) that in order to keep the output to 
1.5kW PEP output, he can't run no more than about 220w of carrier output.

Are you sure -you- know how much PEP your rig is running, without 
distorting/flat-topping the peaks?

--
73, etc
-Geoff/W5OMR




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