Approach to demodulating AM-signals?

Joerg <notthisjoergsch@removethispacbell.net> wrote in
news:iTIOf.44877$H71.44045@newssvr13.news.prodigy.com: 

> Hello Al,
> 
>> 
>> I have probably written more 2105 code than anyone you know, but I
>> can't say I miss it. You can do so much more with just about any DSP
>> today. I think some of the Blackfins are less expensive than the 2105
>> was at $10.00. 
>> 
> 
> Hey, we got them for under $5. For the truck load :-)

The 2105 was originally sold for $9.95 for any quantity. At the time, ADI's 
slightly better part, the 2101 was $50. The 2105 is probably the reason 
that ADI became a player in the DSP market.

> 
> I am no expert in code writing. I worked on algorithms but the code
> was done by folks who knew more about that than I do.
> 
>> 
>> When I was exclusively an analog guy, I used to talk about a DSP core
>> with an ADC and DAC that could replace most of my analog functions.
>> Where DSP solutions were possible, they were usually way to expensive
>> to consider. I'm certainly not anti-analog but I think many solutions
>> are better suited to a DSP approach that were once strictly analog 
>> implementations.
>> 
> 
> True. Nowadays there is so much that can be done digitally. However,
> it almost always (except for some 8051 version) comes with a caveat:
> Single source. One hickup in the production or delivery chain and your
> own production could be toast. I learned to hate that dreaded phrase
> "It's on allocation", meaning only the well-connected will get any
> this quarter. 

I picked the 2105 for a popular ham radio product in 1992. At the same 
time, Motorola put the 56K on allocation. This turned out to be a very good 
business decision on my part. I think that any company that wants both long 
term customers and also wants to provide single sourced parts needs to 
consistly deliver in a timely manner. I certainly have my favorites and 
there are others that I avoid simply due to consistent delivery problems. 
Some companies get it and some don't.

> 
> And think about curb appeal: A nice clear-and-red MELF diode plus a 
> shiny metallic-green film cap versus a bland 144TQFP with some 
> diarrhea-brown 0.1uF decoupling caps. Ok, now I am getting carried
> away here...

Yeh you are getting carried away, these days parts are parts from a curb 
appeal point of view, although I usually think old when I see too many thru 
hole parts. and I still remember the days when I didn't need a microscope 
to solder. I suppose in a few more years I'll reminisce about the days when 
I used lead based solder.

Engineering is all about adapting to change.




> 
> Regards, Joerg
> 
> http://www.analogconsultants.com
> 



-- 
Al Clark
Danville Signal Processing, Inc.
--------------------------------------------------------------------
Purveyors of Fine DSP Hardware and other Cool Stuff
Available at http://www.danvillesignal.com

Hello Al,

> 
> The 2105 was originally sold for $9.95 for any quantity. At the time, ADI's 
> slightly better part, the 2101 was $50. The 2105 is probably the reason 
> that ADI became a player in the DSP market.
> 

Hmm, then we must have gotten a special deal. And it wasn't in the US so 
maybe the pricing wasn't always the same around the globe.

> 
> I picked the 2105 for a popular ham radio product in 1992. At the same 
> time, Motorola put the 56K on allocation. This turned out to be a very good 
> business decision on my part. I think that any company that wants both long 
> term customers and also wants to provide single sourced parts needs to 
> consistly deliver in a timely manner. I certainly have my favorites and 
> there are others that I avoid simply due to consistent delivery problems. 
> Some companies get it and some don't.
> 
> 
Analog Devices is quite good about delivery and very consistent. That is 
one of the very few companies that I'd trust with single source. Then 
there are some that ended up on my blacklist. And I absolutely won't use 
boutique parts or panacea chips if there is any other option.

> 
> Yeh you are getting carried away, these days parts are parts from a curb 
> appeal point of view, although I usually think old when I see too many thru 
> hole parts. and I still remember the days when I didn't need a microscope 
> to solder. I suppose in a few more years I'll reminisce about the days when 
> I used lead based solder.
> 
> Engineering is all about adapting to change.
> 

But the eyes aren't. Just a few minutes ago I switched to a 21" monitor 
on this PC. Ah, what a relief. Now I can read your post without glasses.

Regards, Joerg

http://www.analogconsultants.com

"Mr M" <blobb@bredband.net> wrote in message
news:440b34f7$0$15795$14726298@news.sunsite.dk...
> More info about the project:
>
>
>
> We want to make a digital demodulator because:
>
>
>
> 1.)    we want to be able to make modifications to the signal processing
in
> the future
>
> 2.)    we want small size
>
A diode and a small amp.
> 3.)    we want to get rid of a lot of analog tolerances
>
>
Analogue works, if you have too many such problems you are doing it wrong.

>
>

Al Clark <dsp@danvillesignal.com> writes:
> [...]
> I still remember the days when I didn't need a microscope

Amen, brother. Remember Heathkit? Too bad the miniturization 
of electronics has made this sort of hobby obsolete. 
-- 
%  Randy Yates                  % "...the answer lies within your soul
%% Fuquay-Varina, NC            %       'cause no one knows which side
%%% 919-577-9882                %                   the coin will fall."
%%%% <yates@ieee.org>           %  'Big Wheels', *Out of the Blue*, ELO
http://home.earthlink.net/~yatescr

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:GsKOf.39792$F_3.36569@newssvr29.news.prodigy.net...
> Hello Tim,
>
> >>
> > If you know the phase shift then synchronous demod will probably work
> > well.  I would have suggested it except that it's a pain to lock onto
> > the carrier -- but hey, you have that already.
> >
>
> Or do the full I/Q scheme and it'll tell you the phase.
>
> Regards, Joerg
>
> http://www.analogconsultants.com

If you want the best AM demodulation  then you need to recover the carrier
via squaring then lock into twice the carrier freq using a PLL. Then divide
this freq by 2 and multiply and filter times the original AM. Synchronous AM
demodulation - you don't need a processor of any description.You may well
need an amplitude locked loop first before the PLL however to handle low
SNRs but that's another story. This would be done in software but I don't
see the point.


Tam

Mr M wrote:
> More info about the project:
> 
> 
> 
> We want to make a digital demodulator because:
> 
> 
> 
> 1.)    we want to be able to make modifications to the signal processing in
> the future
> 
> 2.)    we want small size

A surface mount diode and two caps; one to AC couple, the other to 
integrate -- is not a large assemblage of parts.

> 3.)    we want to get rid of a lot of analog tolerances

20% parts will work just fine.

> The unit creates a carrier wave that is sent through a medium. The medium
> AM-modulates the signal. So the receiver end in the unit receives an
> AM-modulated signal. The carrier wave can be selected from about 30 kHz up
> to 100 kHz. And the AM-bandwidth we are interested in is 10 kHz. So if the
> carrier is 50 kHz the received AM-signal is between 45 kHz to 55 kHz.
> 
> 
> 
> The medium contains interference so we want to be able to move our carrier
> frequency to the "quietest" region of this band (30 kHz  to 100 kHz).
> 
> 
> 
> The transmitter is in the same unit as the receiver. We could maybe make a
> synchronous detector?

Sure. Use a pair, one driven by the carrier, the other by the carrier 
phase shifted 90 degrees. (Probably both out of the same oscillator.) 
That's 8 more diodes and a 4 resistors. Here, matching matters.

> And thank you all for the answers I have received so far.
> 
> 


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

Hello Tam,

> 
> If you want the best AM demodulation  then you need to recover the carrier
> via squaring then lock into twice the carrier freq using a PLL. Then divide
> this freq by 2 and multiply and filter times the original AM. Synchronous AM
> demodulation - you don't need a processor of any description.You may well
> need an amplitude locked loop first before the PLL however to handle low
> SNRs but that's another story. This would be done in software but I don't
> see the point.
> 
>
I just pointed out I/Q in case the OP needs to recover phase 
information. Else a simple AM detector should suffice.

And I'd still do it with a diode and a cap (ducking for cover now...).

Regards, Joerg

http://www.analogconsultants.com

Hello Randy,


>>[...]
>>I still remember the days when I didn't need a microscope
> 
> Amen, brother. Remember Heathkit? Too bad the miniturization 
> of electronics has made this sort of hobby obsolete. 


It's really the lack of interest of today's kids in true creativity that 
has caused Heathkit to go down, and the hobby along with it.

Regards, Joerg

http://www.analogconsultants.com

Hello Jerry,

> 
> A surface mount diode and two caps; one to AC couple, the other to 
> integrate -- is not a large assemblage of parts.
> 

Might need a resistor as well. Oops, that would be another 1.5 Cents.

If precision, large dynamic range and linearity are a concern the 
reversed transistor might be an option.

Regards, Joerg

http://www.analogconsultants.com

Joerg <notthisjoergsch@removethispacbell.net> wrote in news:Be2Pf.19621
$rL5.5958@newssvr27.news.prodigy.net:

> Hello Randy,
> 
> 
>>>[...]
>>>I still remember the days when I didn't need a microscope
>> 
>> Amen, brother. Remember Heathkit? Too bad the miniturization 
>> of electronics has made this sort of hobby obsolete. 
> 
> 
> It's really the lack of interest of today's kids in true creativity 
that 
> has caused Heathkit to go down, and the hobby along with it.
> 
> Regards, Joerg
> 
> http://www.analogconsultants.com

I don't think that kids are so different. 

Some of my earliest projects used tubes that usually lit up and then 
smoked.

Later I discovered transistors and I remember scoring an early 4000 CMOS 
book (or maybe it was 7400?)

Today's kids might be building web sites or writing Visual C programs. 
Tools and ingredients change over time. The drive for some people to 
create something or build something is still much the same.

There's not an easy path today for a kid to start building hardware. It 
takes quite a bit of money for basic tools, etc. The computer is already 
at home and available.

If you want to help create a next generation hardware engineer, find the 
right kid and offer to help him (or her) to get started. The kids are out 
there.

-- 
Al Clark
Danville Signal Processing, Inc.
--------------------------------------------------------------------
Purveyors of Fine DSP Hardware and other Cool Stuff
Available at http://www.danvillesignal.com