[ARC5] Lopsided modulation

[Glen Zook]

Having been associated with the commercial two-way FM arena for decades, I can definitely say that most male voices are not symmetrical and most female voices are symmetrical.

Although the modulation used in that industry is either true FM or, with most of the older equipment, PM, this asymmetrical characteristic can be easily seen when measuring the deviation.  When using an oscilloscope type of deviation "meter", this asymmetrical difference is very easy to see.  But, even with the older, analog type of unit where an actual meter is used, if one looks closely, when switching between the low side and high side of the deviation, the difference can be detected.

When setting the deviation, many two-way technicians say the word "five" because that particular word usually produces the maximum amount of deviation.  Often, the word is drawn out as "fivvvvvvvvvvvvve".  When a male talks into the microphone, the difference between the "sidebands" can be significant.  During the decades when +/- 5 kHz deviation was the limit, often the male voice would produce, on the "+" side 5 kHz but on the low side often not more than 4 kHz with some voices producing, maybe, 4.5 kHz.  But, when a female would talk into the microphone, the "sidebands" are, for all practical purposes symmetrical.

When I owned the company, I never did have any female technicians.  However, I always had a secretary (several different women over the years) and when some outsider would say that there was no difference in the voice characteristics, I would have them talk into a microphone (the person was always a male) and then have my secretary talk into the microphone.  That would convince the person that there was a difference between male and female voices.

Now, I admit that I have not really done any experimentation with AM and, as such, I cannot definitely say that this asymmetrical voice characteristic can cause the same difference with the sidebands as it does with FM.  However, my "gut feeling" is that it just might be the cause with AM as well as with FM.
 Glen, K9STH 
Website: http://k9sth.net

      From: J Mcvey via ARC5 <arc5 at mailman.qth.net>
 To: AKLDGUY . <neilb0627 at gmail.com>; ARC-5 List <arc5 at mailman.qth.net> 
 Sent: Monday, February 26, 2018 4:40 PM
 Subject: Re: [ARC5] Lopsided modulation
   
My TX dynamotor only sags about  35V between standby and transmit. Probably contributes to the "chirp" on CW, but I don't think AM modulation would drag it down that much.. I'm using a 25V 65 amp SMPS to drive it , so once it starts, there's lots of current available for steady operation. I get about 50W cw, 22 watts on AM carrier.  My SCR274 is all unmodified circuitry, though, just like they did it on the B-17.

Someone mentioned that it may be that voice has more negative spikes . This may indeed be the case. I know mine does! Take a look at it on a scope while holding  a tone. Try different octaves.  Not very symmetrical at all. The only way to test reproduction symmetry, is to use a sine wave iat say, 1 Khz and see what that looks like.
jim 
   
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