[ARC5] Lopsided modulation

[Bob kb8tq]

Hi

The bottom line is that as long as the carrier is still there, a diode detector will do it’s 
job. Good old analog TV is one classic example of carrier + single sideband (VSB to
be fully accurate). You can have the sidebands a bit out of whack and it still sounds 
like AM in a conventional detector. Take out the carrier and things get wonky ….

Again, toss into the mix that we aren’t dealing with audiophile systems here. A bit of 
distortion is not at all unusual in modulator circuits or in typical AM detectors. The one
thing that likely is not messed up in a “typical” WW II receiver is the sideband balance. 
The broad tuning that is so often discussed helps in that respect. Crystal and mechanical 
filters (and their issues) came along later ….

Bob

> On Feb 28, 2018, at 10:06 PM, George Babits <gbabits at custertel.net> wrote:
> 
> For all the theoretical mumbo jumbo that this thread has generated, the bottom line is really  "what does it sound like on the other end?"  If it sounds good, who cares.  I think this whole thing has been completely beaten to death!
> 
> George
> W7HDL
> 
> 
> ----- Original Message ----- From: "D C _Mac_ Macdonald" <k2gkk at hotmail.com>
> To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>; <arc5 at mailman.qth.net>
> Sent: Wednesday, February 28, 2018 7:41 PM
> Subject: Re: [ARC5] Lopsided modulation
> 
> 
> Finally, some 'splainin' that makes some sense!
> 
> 
> 73 de Mac, K2GKK/5
> (Since 30 Nov '53)
> Oklahoma City, OK
> USAF Retired 61-81
> FAA Retired 94-10
> ________________________________
> From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> on behalf of Richard Knoppow <1oldlens1 at ix.netcom.com>
> Sent: Wednesday, February 28, 2018 13:31
> To: arc5 at mailman.qth.net
> Subject: Re: [ARC5] Lopsided modulation
> 
>   For the asymmetrical voice begin by visualizing a sine wave
> with a line to indicate the zero volts going along the center.
> Now, imaging a sine wave with one side flattened. That is
> asymmetrical. If the center line is still in the same place the
> voltage on one side is larger than the voltage on the other.
>   The human voice is generated by forcing air from the lungs
> past the vocal cords. The vocal cords act as a valve. Since the
> pressure is in one direction only the modulated air stream is
> mostly more positive pressure than the average air pressure.
> However, since the voice is also partially generated by a number
> of resonant chambers in the throat and head, which are after the
> vocal cords, the pressures are modified so that its not all more
> positive than the average air pressure. The displacement from
> average depends on the individual voice: some voices are very
> asymmetrical, some are more nearly symmetrical. I don't think any
> are more negative going because the voice starts out as a
> positive pressure from the lungs. The vocal cords can vary or
> modulate this pressure but can not reverse it.
>    If one picks up the voice with a purely pressure sensitive
> microphone the asymmetry is reproduced as an asymmetrical
> electrical wave form. However, since microphones have some
> resonances the symmetry or lack of it may be affected. Some
> microphones, namely the figure eight type or cardioid type are
> sensitive to either air particle velocity (figure 8) or both
> velocity and pressure (cardioid). The figure-8 pattern results
> from sensing a pressure difference between two points in the
> pressure wave so the microphone, in effect, performs a first
> order differential on the wave, and thus looses any constant
> pressure. That results in a waveform which may be asymmetrical
> but not in the same way the original pressure wave was
> asymmetrical. All this is made much clearer with a couple of
> drawings than it is in words.
>    In any case, if you have an oscilloscope attach a microphone
> to it and talk into it. You don't even need a modern scope, one
> that responds to audio frequencies is adequate. The scope should
> be DC coupled. It will show the asymmetry in the voice.
> 
> --
> Richard Knoppow
> 1oldlens1 at ix.netcom.com
> WB6KBL
> 
> 
> 
> --------------------------------------------------------------------------------
> 
> 
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