[AMRadio] Side band power with increased carrier/wasclippertononAM

[Jim Wilhite]

Hey Gary,

You are correct but this is where many people get lost.  They translate 
one impedance or voltage in a part of the calculations then forget to 
carry it to the next place.  Also, invariably, a discussion breaks out 
about the difference between the single tone modulation and the voice. 
Then we get deep into the weeds and loose the discussion in the details. 
That example you gave earlier is plain spoken and easy to understand for 
almost everyone mainly because it references one value of voltage and 
impedance.  It is very difficult for some people to understand that a 
spectrum analyzer makes measurements from a relative value not a fixed 
value like a voltmeter or wattmeter.

The scope is probably the best thing to monitor a wave form be it a 
single tone or voice modulation.  Either that or a monitor scope like 
the ones Kenwood or Yaesu makes.  If people understand what you 
described and have that scope, they can keep a very good signal going 
out the antenna.

I am almost paranoid about all this because out near where I live there 
are some guys who think the average meter reading should be 120 ma (or 
what ever) on the modulation meter, when the book says that your meter 
should PEAK to that value.  The average will be much less than that, 
normally about 1/3 to 1/2 of the peak.  But explaining what I mean by 
average is difficult without the aid of a physical presentation.  Hard 
to do here.  The guys I speak about around here splatter all over the 
place making it uncomfortable or impossible for me to operate within 
10-15 Kc. of the normal gathering place.

73

Jim/W5JO


----- Original Message ----- 

> Hi Jim,
>
> It doesn't matter about the 50 ohm antenna line impedance. You could 
> use any
> impedance that you want as long as you use the same impedance for all 
> the
> calculations. This just gives a comparison. John used 4000 ohms plate
> impedance for his calculations. That of course gives different 
> voltages than
> those that I showed but as long as everything is referenced to that 
> same
> impedance it doesn't matter. All the relations work out the same. Just 
> ohms
> law at work.
>
> The modulation waveform shape is not too important when looking at 
> maximum
> modulation on negative peaks and positive peaks that determine Peak 
> envelope
> power. In the real world with voice modulation all we need to do is 
> use a
> scope to see all of this. As an example at 375 watts carrier set the 
> scope
> to read 4 divisions on just carrier. When modulation peaks hit 8 
> divisions
> on the scope that is 1500 watts PEP (2x the voltage). When negative 
> peaks
> hit the base line that is 100% modulation in the negative direction. 
> All you
> really need to know except that the more high peaks the audio has the 
> lower
> the average audio power in the side bands will be.
>
> A sin wave is just easier to look at and do calculations with than a 
> voice
> wave form is for understanding what is happening.
>
> Further you can look at the number of divisions on the scope that the 
> audio
> occupies. The more divisions the greater the audio power on the 
> signal. If
> you raise the carrier above the 375 watt level you will not hit the 
> 100%
> mark on negative peaks as soon but you will sooner hit the 1500 watt 
> PEP
> mark and you will have less total divisions of audio on the scope. 
> This
> means less audio power transmitted.
>
> 73
> Gary  K4FMX
>