[AMRadio] Power Levels

[Wt8r at aol.com]

In a message dated 6/29/02 8:29:33 PM Eastern Daylight Time, 
bbruhns at erols.com writes:


> Hi Dave,
> 
> It's nothing personal, Dave.  Elmer is just tired of this
> subject.  He was tired of it when the thread began, and he's
> REALLY sick of it now.  Sorry, Elmer.
> 
> Modulation does interesting things in AM.  500W input, 375W
> output is roughly true of the CW carrier, but then we apply
> AM to the carrier.  With 100% symmetrical modulation, this
> varies the carrier amplitude from its normal level up to
> twice carrier voltage on positive peaks, and down to zero on
> negative peaks.
> 
> With a resistive load (which we have), doubling the voltage
> results in doubling the current.  But when both the voltage
> and current are doubled, the power is multiplied by four.
> Hence with 100% symmetrical modulation, and likewise with
> any AM modulation waveform producing 100% positive
> modulation, PEP = 4 * carrier.   .
> 
> In fact, the average overall output power level increases to
> 1.5 times carrier power level with 100% sinusoidal AM.  This
> is where the extra power goes that the modulator provides.
> 
> It's an interesting subject.  Sometimes it doesn't seem to
> make sense, but it really does.
> 
> Another fine point: the carrier itself is a sine wave.  When
> we modulate it, it is slightly distorted from a sine wave
> because it is changing in amplitude.  But these change are
> usually very slow compared to the carier frequency, so we
> ignore them.  The carrier is essentially a sine wave.  This
> is what the FCC is talking about when they say that the peak
> RMS power of the RF envelope shall not exceed 1500 watts,
> averaged over a carrier cycle.  This was to avoid ambiguity
> about the meaning of peak level.  It could have meant the
> peak voltage that the carrier sine wave reached, which would
> be 1.414 times the RMS; in this 1500W PEP example, the power
> at that instant would be 3000 watts.  But that's not what
> they meant; they meant the peak RMS level on a one-cycle RF
> timescale.
> 
>   Bacon, WA3WDR
> 
> 

Bacon,

       Thank you for your reasoned response.  I would expect nothing less 
from a group of real amateur radio operators.

       My comment about the morons applies only to Elmer Dud and I would 
expect that he is frustrated because he can't cut the mustard in 
understanding the theory or just gets his enjoyment from trying to belittle 
others he feels inferior to. 

       I read posts from this list for about a week before joining it and I 
saw quite a bit of ignornace and misinformation being spewed forth.

       It is difficult to believe that testing for Advanced and Extra Class 
licenses has become such a farce.

       Again, thank you.


73 de
Dave in Dayton, WT8R


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