AM Modulation

It is an imperfection to modulate the Vcc of the transmitter element when it could just as easily linearly amplify the SSB without all that mess. And the telemetric ASK type of AM modulation is a prevalent form of direct multiplication.

I think the classic plate-modulated output stage was more electrically efficient than going linear on the final and modulating upstream. One reason was that it was usually running class C for efficiency, and class C amps aren't linear [1]. Another is that for audio broadcast, most of the time the program level is low, mostly carrier, and it's better for efficiency if the plate voltage is optimized for that power level. Plate modulation lets the plate supply voltage track the dynamic operating level, pretty clever optimization after all.

Pretty much, the plate DC supply furnishes the carrier power, and the transformer-coupled modulation supply furnishes the sideband power. If the AF modulator amp runs class B, as they usually did, and the RF final runs class C, the whole mess is efficient and you get lots of power from the final jug.

AM transmitters are, what, PWM now?

John

[1] Duh. Plate modulating a class A stage wouldn't modulate at all.

"John Larkin" snipped-for-privacy@ieee.org

** Everything Da Slow Man posts is just plain silly

** He simply can't do that.

He has a serious mental disability he is incapable of facing.

........ Phil

Probably not a real disability; BS is adequately intelligent. I suspect he posts to newsgroups mostly to show how smart he is, and/or how dumb other people are. Lots of people, too many people, do that. It's about ego, not electronics.

Such an attitude is inconsistant with admitting mistakes. And not admitting mistakes is inconsistant with ever learning anything new.

John

"John Larkin"

** It is the most common one of all, among academics, programmers and technical folk. ** Nought to do with having a specific mental disability though. One that inhibits the capacity to appreciate the implied context held in the minds of others.

BTW:

Da Slow Man has stated, right here on SED, that has Asperger's syndrome.

** AKA - being a legend in his own mind.

** As the word of a famous Aussie pop song say:

" .... ego is not a dirty word ... " ( Skyhooks )

But " egomaniac " is.

** Do academics or engineers EVER admit their mistakes ???

No matter how heinous ??

No - others have to suffer the consequences while they live in protective isolation, courtesy of the institutions they infest and/ or the embarrassed employers that hide them away.

** When the pioneer economist Adam Smith was chided with the question -

" How can anyone believe you when you are constantly altering your theories ? "

he succinctly replied:

" Whenever I discover I am wrong, I always change my mind.

Don't you ?? "

....... Phil

I do. When I make a really good blunder, I walk around and tell all my other engineers about it, and sometimes my customers too. I relish stories of truly monumental mistakes, particularly my own. The aim is to not have them make the same goof, but more importantly establish a culture of openness about the hazards of designing complex systems. It's working: when one of my guys has something funny going on, he's likely to come to me, or to another engineer, and have the other person look at his work and help him find the bug. It's amazing how someone else's insight can help, or even how many mistakes are found by merely having to explain something out loud to someone else. When a mistake is found this way, we say "Gotcha! cool! thanks!" instead of getting all resentful about being caught making a mistake. Some blunders are dumb and some are subtile works of beauty.

Newsgroups are especially unforgiving of mistakes; some dork will always jump on you if you say anything even slightly off, or define something a way they don't like, or spell something wrong. That environment is sheer poison to invention.

Circuit design consists somewhat, and programming consists primarily, of the management of mistakes.

John

[snip]

Me too. My mistakes are so funny. Particularly when I get in contact with high voltage while the techs are standing there.

William L. Petersen as Gil Grissom on CSI said on last night's episode, "I make mistakes and I learn from them".

[snip]

Explaining how you idea works "out loud" to someone else works great at finding mistakes... particularly when there's a large crowd watching. I once had a crowd claim I staged an explosion while I was doing a demo... neeerp, it was a blunder ;-)

I often hand off a design to a person totally unfamiliar with the project, and tell them, "Have at it".

Yep, even the "subtle" ones. What's "subtile"? Under the floor ?:-)

Absolutely! I've thrown away probably 10 times as many designs as have seen the light of day. Ask my wife. In our first home in Arizona I'd sit at the couch with a quadrille pad (probably 25 years before PC's), wad up bad ideas and toss them over my shoulder into the dining room. Not popular ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
     It\'s what you learn, after you know it all, that counts.

You should have turned the couch so you would have tossed them into a fireplace. ;-)

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

That particular house had no fireplace.

But the house in Cupertino did. I had wet wood, and no regular lighter fluid, so I used acetone. One match flicked into the fireplace produced a momentary room-filling fire ball, and accompanying ash scatter.

The wife didn't even flinch... she just said, "Get the vacuum cleaner."

But I learn from my mistakes... I've never done that again ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
     It\'s what you learn, after you know it all, that counts.

A fireplace? In ARIZONA??? You gotta be shittin' me.

Jim

[snip]

Ummmm? Most of the houses in this neighborhood have fireplaces. They produce enough heat in winter that it's rare that I need to turn on the heat pump.

And I have an outdoor "beehive" fireplace that gets used a lot.

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | It's what you learn, after you know it all, that counts.

Somebody in this thread said something I'd like to check in on. THe comment was made that you can't use high-level AM modulation (collector, drain, plate ...) on a class A (or other linear class) output stage. I'm having trouble wrapping my head around that one. I've never tried high level AM on anything but class C, so I can't argue from experience. But...as Clem Kaddiddlehopper said, "It just don't seem right; it just don't seem right".

Any comments?

Jim

Why? They are common here in Central Florida. They are used to take away the chill on a cool morning, and are great for getting rid of all the paper that people shred these days. I have one in my 40 year old home.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

One of those early fire rescue TV shows had an episode where a man and his friend built a fireplace. They just couldn't wait for the mortar to dry, so they built a fire and it exploded from the water vapor. :)

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

--
Now you make _her_ get the vacuum cleaner? ;)

Liquid oxygen makes an excellent barbeque starter.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
Synergetics   3860 West First Street   Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml   email: don@tinaja.com

Please visit my GURU\'s LAIR web site at http://www.tinaja.com

Much of Arizona is above 8000 feet elevation.

We even had a glacier till global warming did it in.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
Synergetics   3860 West First Street   Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml   email: don@tinaja.com

Please visit my GURU\'s LAIR web site at http://www.tinaja.com

Much of Florida isn't above 80 feet elevation! ;-)

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Fat chance!

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
     It\'s what you learn, after you know it all, that counts.