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From: waltech on 24 Dec 2009 14:26

hello, and thanks everyone for your replies.
I feel like I'm on the same page with everyone.

The basic equation you provided validates my concept of the
offset and shows me where to place the offset.

if I use (a) for audio and (c) for carrier,
2cos(c) + 2cos(a+c) + 2cos(a-c)
implies that a is the carrier on the RHS, but the identity:
cos(x)=cos(-x) =>
2cos(a-c) = 2cos(c-a)
fixes thngs.

Back to physical representation.

If the tube plate of the modulator is connected to top tank
circuit, and the tank bottom is in series with the modulator
( transformer ), which then connects to Eb:

IOW,
If I see a plate circuit, there is the ep, et, em and Eb
Eb is the static plate supply
em is the modulation
et is the plate RF tank
ep is the plate voltage itself.

Then the plate supply ( static )
Eb = et + em + ep

The voltages add. I see no multiplication here.

I have been also taught that non-linear effects make the
modulation. Unless it's evident in this example, I will
ignore it.

However, the only addition two things I can think of that might
in some way contribute to the explanation are:
1. there is some "power" in the calculation that helps explain
the multiplication ( V x I is a multiplication ).
2. the fact the additions above are hiding the "X" effect ( select 1 )
static E's
dynamic e's
??


Not to stray too far from the technical aspects of
how modulation happens and it's translation to DSP,
I would like to know, since I am simulating from a
learning experience ( using C#, not Matlab ), what ( in general )
would be the ratio ( range) of digital modulations often used
with "computers". For example, would someone use a 2 ghz pentium
and a 65536 sized array to simulate a 100 hz signal onto a
5 Mhz ( 50 mhz, 500 Mhz ) carrier ?? Is there a rule of thumb ?
( would it matter if it was some digital modulation or linear ?)


Thanks for your advice.
The thread has been quite enlightening.


Walt......


From: Jerry Avins on 24 Dec 2009 14:43
waltech wrote:
> hello, and thanks everyone for your replies.
> I feel like I'm on the same page with everyone.
>
> The basic equation you provided validates my concept of the
> offset and shows me where to place the offset.
>
> if I use (a) for audio and (c) for carrier,
> 2cos(c) + 2cos(a+c) + 2cos(a-c)
> implies that a is the carrier on the RHS, but the identity:
> cos(x)=cos(-x) =>
> 2cos(a-c) = 2cos(c-a)
> fixes thngs.
>
> Back to physical representation.
>
> If the tube plate of the modulator is connected to top tank
> circuit, and the tank bottom is in series with the modulator
> ( transformer ), which then connects to Eb:
>
> IOW,
> If I see a plate circuit, there is the ep, et, em and Eb
> Eb is the static plate supply
> em is the modulation
> et is the plate RF tank
> ep is the plate voltage itself.
>
> Then the plate supply ( static )
> Eb = et + em + ep
>
> The voltages add. I see no multiplication here.

The modulated stage operated Class-C with a tank Q of about 3. That's
damped enough to allow cycle-to-cycle changes of amplitude, but live
enough to swing the plate up to the power supply when the tube id cut
off. Therefore, the peak RF amplitude follows the modulation voltage
coming out of the transformer (if there is one. See "Heising modulator")

> I have been also taught that non-linear effects make the
> modulation. Unless it's evident in this example, I will
> ignore it.

Multiplication is a non-linear operation. One can also modulate with diodes.

> However, the only addition two things I can think of that might
> in some way contribute to the explanation are:
> 1. there is some "power" in the calculation that helps explain
> the multiplication ( V x I is a multiplication ).
> 2. the fact the additions above are hiding the "X" effect ( select 1 )
> static E's
> dynamic e's
> ??

Don't stretch it.


> Not to stray too far from the technical aspects of
> how modulation happens and it's translation to DSP,
> I would like to know, since I am simulating from a
> learning experience ( using C#, not Matlab ), what ( in general )
> would be the ratio ( range) of digital modulations often used
> with "computers". For example, would someone use a 2 ghz pentium
> and a 65536 sized array to simulate a 100 hz signal onto a
> 5 Mhz ( 50 mhz, 500 Mhz ) carrier ?? Is there a rule of thumb ?
> ( would it matter if it was some digital modulation or linear ?)

AM is rarely used with digital modulation. It is primarily an analog medium.

> Thanks for your advice.
> The thread has been quite enlightening.

You're welcome.

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
From: Mark on 24 Dec 2009 19:50

> AM is rarely used with digital modulation. It is primarily an analog medium.
>
>
Um, what abut QAM? :-)

Mark
From: waltech on 24 Dec 2009 21:47


> One of the multipliers is a constant
> (if you can call RF constant). So gain proportional to plate voltage
> accomplished the multiplication.


I kinda like the way the above sounds.
I want to think on it a bit more.

>
>> AM is rarely used with digital modulation. It is primarily an analog
medium.
>>
>>
>Um, what abut QAM? :-)
>
>Mark


At first, I thought of asking about a BPSK or such
as a radio transmission. QAM will do ..

thanks for mentioning it.

By the way, I ran across a term that suggested low level
modulation using phase and then at the power amp, converting to AM.
The term was ampliphase. Didn't know if it was related to the
discussion on SSB but it sounded a bit like it.


Walt......

From: Jerry Avins on 24 Dec 2009 22:42
Mark wrote:
>> AM is rarely used with digital modulation. It is primarily an analog medium.
>>
>>
> Um, what abut QAM? :-)

:-) indeed! You don't make QAM with a plate modulator, nor do you decode
it with a peak detector.

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
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