John Curl's Blowtorch preamplifier part II - Page 96 - diyAudio
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Old 4th September 2009, 07:36 PM   #951
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Quote:
Originally Posted by janneman View Post
OK, ok, you're right, I should.
Great! Thanks.

Now show us you really mean it and poke some fun at Jam. I have some spare "Yo mama..." jokes you can use if you need a little help.

se
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Old 4th September 2009, 07:44 PM   #952
anatech is offline anatech  Canada
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Hi John,
What I can tell you about FM modulation is from direct experience. A single frequency modulation of a carrier is identical as a single frequency of phase modulation. The HP product manual for the RF generators I have state this clearly. Indeed, if I phase modulate a carrier with 1 KHz and demodulate it using an HP 8901A (modulation analyzer), I get the same result as when I take another HP RF generator and FM modulate the carrier with a 1KHz tone. They also look the same on my spectrum analyzer or oscilloscope as well. So in this case, theory and practice align nicely. I haven't really bothered to try and decipher what happens if you phase modulate a carrier with a complex, multi-frequency signal, but the manuals indicate that phase and frequency modulation differ in those cases.

I figured I would at least report what I have read on this, and also what my direct observations were.

John, I do learn from you when you speak directly and point to the supporting information that is freely available and easy to get at. Beyond that, if you want to make a point, it really is your job to support what you say. If you are going to refer to what another person has said, then direct us to a paper or post that person has made. There is a reason why "hear-say" evidence is not normally admissible in a court of law. A small change in wording can completely change the meaning of a statement. This is why it's dangerous for people to accept what you say without the source. In fact, you don't always completely understand the issue. That's okay and natural, but you must allow that you may be mistaken some times. This is where things break down when you are pushing a point. No evidence that can be confirmed isn't really worth a great deal.

To your other point, yes I am a moderator. However I am also a member. I can and will speak my mind where I see a need. This is exactly what I am doing, like it or not. I think that I've been pretty clear by now on what you do that bothers me. I've stated this again in this post earlier on. Treat people around you with more respect, they do not deserve any less.

-Chris
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Old 4th September 2009, 07:56 PM   #953
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Quote:
Originally Posted by janneman View Post
Not sure who you address or what graph, but reading the posted piece it looks like inharmonic components are created with an inharmonic modulation frequency. How does that relate to the audio amp case discussed, I'm not sure, I'm skating on logic here, not on knowledge, I admit.

Anyway, inharmonic distortion does apparently occur in mechanical systems:

jd
If you "ping" a 10MHz crystal with a square wave you will get some 10MHz out. An amplifier with significant resonant energy storage i.e. class D might be made to make all kinds off stuff. I don't think that is an issue here, and certainly not in the uA741 (I assume a PIM baddie).
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Old 4th September 2009, 08:25 PM   #954
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Chris, I am doing everyone interested, a GREAT BIG FAVOR just bringing up these new 'breakthroughs' (at least for us) in audio design. I don't have to prove this stuff in a court of law. Who cares? I also don't have the time, energy, or patience to write a technical paper about it, these days, and have it published, if possible, after going through the referee process, composed of guys like Bob Cordell or Scott Wurcer. Why would I bother? Although I have written articles for journals and magazines, in the long past, 30 years ago, when I thought it important to do so. It just isn't worth it, today.
Everyone, take it, disprove it, or leave it. It is your gain or loss, not mine.
Except, Nelson, Charles, and I aren't even considered design engineers by you, even though Humphrey Ins put 'Sr Design Engineer' on my business card, 25 years ago.
However, I prefer 'Vice President of Engineering' the title on my business card with LINEAGE INC. more than 20 years ago.
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Old 4th September 2009, 08:25 PM   #955
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Quote:
Originally Posted by Bob Cordell View Post
I was always taught that narrowband fm is essentially like am but with the phase of the sidebands just different. I completely understand that this is not the case for high-deviation fm, where Bessel functions are essential to a proper understanding (but I do not believe that PIM falls in the category of high-deviation fm).
You are right here absolutely, about phase of sidebands: yesterday I've posted the link on an article that deals with "How to tell, is it AM or FM"? It seems to me, nobody paid attention.
The truth is, quadrature modulation was used in radio for FM modulation. I.e. the case of modulation of one sine wave by some signal. Products are harmonically related. But in case of phase inter modulation the result is a quite different garbage.
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Old 4th September 2009, 08:31 PM   #956
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So this is the Fig 3 John has brought up. What is that confounded 'blip'?

jd
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Old 4th September 2009, 08:32 PM   #957
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Wavebourn, the article has to be PURCHASED. Why don't you buy it, and tell us what it gives to the discussion? Puts a different emphasis on it, doesn't it?
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Old 4th September 2009, 08:36 PM   #958
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Janeman, look at around 5K and 1K for a balanced pair of sidebands. NOTE that they have no ID on them.
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Old 4th September 2009, 08:36 PM   #959
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John;
I wish I did not throw out my conspects of lectures long time ago, they were free of charge...
I've searched the Web yesterday and found that article, unfortunately it was not free. But I believe any existing elementary textbook for radio engineers may be used.
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Old 4th September 2009, 08:39 PM   #960
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ok...stirr it up again...what if the measured distortion/intermodulation spectra is clean, without sidebands, harmonics etc.
Do we still blame a high feedback approach as sounding bad?
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