Synchronous AM demodulation (again...)

Okay - I think I will miss something to answer but I'll do my best.

I know that what a professor is telling me is not the best thing everytime.
What I wanted to say is that I will try to hold my requirements. That's it.
If there's another and better solution I'll do it. But I have to proof it.

That brings me to my next point, the analoge understanding: I understand
the envelope detector with a diode. That's what we're using right now. I
read a bunch of things about demodulation and sync. AM demod but I didn't
find a source that gives me a great understanding about it. That's why I
ask about a book. Especially a source which comes to the point to use
complex numbers. I will take a look at ARRL handbook - didn't know that
before.

I also know that making things complex just because you can mustn't be good
(like the "Hello World" example between a beginner, a semi pro and a pro).
But I should do the demodulation and filtering inside a DSP and I'm excited
to do this 'cause I'm new in this business and I will do my next grade on
this topic (I've decided during the last 3 semesters that digital signal
processing and embedded systems are more or less my world). So why not
using a DSP.

Sure, there are a bunch of ways to get rid of the carrier. But this is
actualy not what it is supposed to do.

>Remains only the real world problem: would a marginaly
>improved performance be relevant relative to the more complex
>circuit ?

What do you mean? Do you mean why I've chosen a 1MHz ADC?


Please let me know if I missed somthing.

I've heard today that they fixed the device. So I will go there and see if
I can run some tests with filters and a transformer to see what happens.

Tim Wescott <tim@seemywebsite.com> wrote:
(someone else wrote

>> What is the point? Digital is going to be about 100 times more expensive
>> and 10 times more complex.
 
> If the prof wants it done with a DSP then that's the "right" solution, 
> regardless of how it may survive in the commercial world.

But can't you at least subtract some of the carrier before
going digital?  Not all of it, such that the demodulation
is still in the digital side, but without such a huge 
background to hide the signal.

-- glen 

AlanWrench <stud.magraf@n_o_s_p_a_m.googlemail.com> wrote:
(snip)
 
> I also know that making things complex just because you can mustn't be good
> (like the "Hello World" example between a beginner, a semi pro and a pro).
> But I should do the demodulation and filtering inside a DSP and I'm excited
> to do this 'cause I'm new in this business and I will do my next grade on
> this topic (I've decided during the last 3 semesters that digital signal
> processing and embedded systems are more or less my world). So why not
> using a DSP.

(snip)

Well, often this works.  Digital electronics (assuming economy
of scale) is often enough cheaper than analog electronics that
it does make sense.

Still, you (usually) need to understand the analog problem and
solution.  

It seems to me that, at least in the beginning, you should
subtract some of the carrier before digitizing.  It isn't
that hard to do, and isn't really demodulation.  (That is,
you aren't cheating.)  Maybe later it will turn out to be
more economical to just digitize the 500V signal, but 
maybe not at first.

-- glen

On 10/06/2010 01:14 PM, glen herrmannsfeldt wrote:
> Tim Wescott<tim@seemywebsite.com>  wrote:
> (someone else wrote
>
>>> What is the point? Digital is going to be about 100 times more expensive
>>> and 10 times more complex.
>
>> If the prof wants it done with a DSP then that's the "right" solution,
>> regardless of how it may survive in the commercial world.
>
> But can't you at least subtract some of the carrier before
> going digital?  Not all of it, such that the demodulation
> is still in the digital side, but without such a huge
> background to hide the signal.
>
> -- glen

Certainly if you can use dropping transformers you ought to be able to 
do that.  Particularly if you have to do some digital magic to get 
things phased right.

If you do you'll probably have to filter the square wave from the 
processor, so you're just subtracting fundamental from fundamental.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On 10/06/2010 01:21 PM, glen herrmannsfeldt wrote:
> AlanWrench<stud.magraf@n_o_s_p_a_m.googlemail.com>  wrote:
> (snip)
>
>> I also know that making things complex just because you can mustn't be good
>> (like the "Hello World" example between a beginner, a semi pro and a pro).
>> But I should do the demodulation and filtering inside a DSP and I'm excited
>> to do this 'cause I'm new in this business and I will do my next grade on
>> this topic (I've decided during the last 3 semesters that digital signal
>> processing and embedded systems are more or less my world). So why not
>> using a DSP.
>
> (snip)
>
> Well, often this works.  Digital electronics (assuming economy
> of scale) is often enough cheaper than analog electronics that
> it does make sense.
>
> Still, you (usually) need to understand the analog problem and
> solution.
>
> It seems to me that, at least in the beginning, you should
> subtract some of the carrier before digitizing.  It isn't
> that hard to do, and isn't really demodulation.  (That is,
> you aren't cheating.)  Maybe later it will turn out to be
> more economical to just digitize the 500V signal, but
> maybe not at first.

Besides, one always has to do _some_ signal conditioning to get a signal 
into and ADC.  The question is always "how much", the answer is almost 
always "whatever works well and minimizes the lifetime cost of the 
system", and the argument always starts when you try to pin down the answer.

I suspect that in your case subtracting out some of the carrier is a 
good candidate for the best answer, but it may not be at all -- so 
you've got to check (and run things by your prof).

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

What would be a good signal conditioning before going into the ADC?

We had some discussion today and we figured out two plans:
 1) I will wire a transformer just to see how the signal at the output
looks 
    like
 2) When I have my stuff I will use the diode envelope detector and go
after 
    that into a ADC and from there to the DSP. If the whole thing is
working 
    with this and I have time I will see if the transformer version works
or 
    not

I am still looking for something to read like a book about the analog thing
(envelope detector, other solutions) ... anyone has a good idea for that?

AlanWrench wrote:

> What would be a good signal conditioning before going into the ADC? 
> We had some discussion today and we figured out two plans:

>  1) I will wire a transformer just to see how the signal at the output
> looks 
>     like
>  2) When I have my stuff I will use the diode envelope detector and go
> after 
>     that into a ADC and from there to the DSP. If the whole thing is
> working 
>     with this and I have time I will see if the transformer version works
> or 
>     not
> 
> I am still looking for something to read like a book about the analog thing
> (envelope detector, other solutions) ... anyone has a good idea for that?

Idiot

>
>
>AlanWrench wrote:
>
>> What would be a good signal conditioning before going into the ADC? 
>> We had some discussion today and we figured out two plans:
>
>>  1) I will wire a transformer just to see how the signal at the output
>> looks 
>>     like
>>  2) When I have my stuff I will use the diode envelope detector and go
>> after 
>>     that into a ADC and from there to the DSP. If the whole thing is
>> working 
>>     with this and I have time I will see if the transformer version
works
>> or 
>>     not
>> 
>> I am still looking for something to read like a book about the analog
thing
>> (envelope detector, other solutions) ... anyone has a good idea for
that?
>
>Idiot
>
>

A very kind and smart way to greet new guys on the board ... Actually I
don't know why I should be a idiot or rather why you call me one.
Maybe because I use the time during waiting for my stuff to see why a
transformer is bad or I am a idiot 'cause I am looking for books to read
and inform myself (besides the ARRL Handbook and Understanding Digital
Signal Processing).

But okay. It's your opinion though.
Cheers and thanks for helping me so far.

AlanWrench <stud.magraf@n_o_s_p_a_m.googlemail.com> wrote:
(someone wrote)

>>Idiot
 
> A very kind and smart way to greet new guys on the board ... Actually I
> don't know why I should be a idiot or rather why you call me one.
> Maybe because I use the time during waiting for my stuff to see why a
> transformer is bad or I am a idiot 'cause I am looking for books to read
> and inform myself (besides the ARRL Handbook and Understanding Digital
> Signal Processing).

You get used to him after a while.  

-- glen

>AlanWrench <stud.magraf@n_o_s_p_a_m.googlemail.com> wrote:
>(someone wrote)
>
>>>Idiot
> 
>> A very kind and smart way to greet new guys on the board ... Actually I
>> don't know why I should be a idiot or rather why you call me one.
>> Maybe because I use the time during waiting for my stuff to see why a
>> transformer is bad or I am a idiot 'cause I am looking for books to
read
>> and inform myself (besides the ARRL Handbook and Understanding Digital
>> Signal Processing).
>
>You get used to him after a while.  
>
>-- glen
>

Doesn't make it better ... Everyone of use was in the situation to be the
newbee and no one would like a post like this ...