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From: MRW on 16 Feb 2010 01:22
Hello group,

I posted a screen capture of an image showing a basic Amplitude Shift
Key modulation:
http://imgur.com/Ahwya.jpg

The image shows the a diagram and equation. The equation is ASK(t) =
s(t)*sin(2*pi*f*t). I assume s(t) is the baseband signal and
sin(2*pi*f*t) is the carrier frequency.

In the image, is it possible for s(t) to have a higher frequency as
sin(2*pi*f*t)? Please explain.

Thanks!

From: Greg Neill on 16 Feb 2010 07:45
MRW wrote:
> Hello group,
>
> I posted a screen capture of an image showing a basic Amplitude Shift
> Key modulation:
> http://imgur.com/Ahwya.jpg
>
> The image shows the a diagram and equation. The equation is ASK(t) =
> s(t)*sin(2*pi*f*t). I assume s(t) is the baseband signal and
> sin(2*pi*f*t) is the carrier frequency.
>
> In the image, is it possible for s(t) to have a higher frequency as
> sin(2*pi*f*t)? Please explain.
>
> Thanks!

Try drawing such a case. How would a receiver interpret
the resulting signal?


From: George Herold on 17 Feb 2010 14:44
On Feb 16, 1:22 am, MRW <mr.whate...(a)gmail.com> wrote:
> Hello group,
>
> I posted a screen capture of an image showing a basic Amplitude Shift
> Key modulation:http://imgur.com/Ahwya.jpg
>
> The image shows the a diagram and equation. The equation is ASK(t) =
> s(t)*sin(2*pi*f*t). I assume s(t) is the baseband signal and
> sin(2*pi*f*t) is the carrier frequency.
>
> In the image, is it possible for s(t) to have a higher frequency as
> sin(2*pi*f*t)? Please explain.
>
> Thanks!

OK I'm probabbly being an idiot here... But is that picture right?
You don't want the carrier to go to zero amplitude do you? Isn't this
like AM radio?

George H.
From: John Fields on 17 Feb 2010 15:45
On Wed, 17 Feb 2010 11:44:01 -0800 (PST), George Herold
<ggherold(a)gmail.com> wrote:

>On Feb 16, 1:22�am, MRW <mr.whate...(a)gmail.com> wrote:
>> Hello group,
>>
>> I posted a screen capture of an image showing a basic Amplitude Shift
>> Key modulation:http://imgur.com/Ahwya.jpg
>>
>> The image shows the a diagram and equation. The equation is ASK(t) =
>> s(t)*sin(2*pi*f*t). I assume s(t) is the baseband signal and
>> sin(2*pi*f*t) is the carrier frequency.
>>
>> In the image, is it possible for s(t) to have a higher frequency as
>> sin(2*pi*f*t)? Please explain.
>>
>> Thanks!
>
>OK I'm probabbly being an idiot here... But is that picture right?

---
Yeah.
---

>You don't want the carrier to go to zero amplitude do you? Isn't this
>like AM radio?

---
No; in this case the presence of a carrier denotes a transmission of a
"1", say, and the length of time the carrier is ON defines how many 1's
will be transmitted.

Conversely, the absence of a carrier denotes the transmission of a zero
and the length of time there is no carrier defines how many zeros will
be transmitted.


JF
From: George Herold on 17 Feb 2010 16:32
On Feb 17, 3:45 pm, John Fields <jfie...(a)austininstruments.com> wrote:
> On Wed, 17 Feb 2010 11:44:01 -0800 (PST), George Herold
>
>
>
>
>
> <ggher...(a)gmail.com> wrote:
> >On Feb 16, 1:22 am, MRW <mr.whate...(a)gmail.com> wrote:
> >> Hello group,
>
> >> I posted a screen capture of an image showing a basic Amplitude Shift
> >> Key modulation:http://imgur.com/Ahwya.jpg
>
> >> The image shows the a diagram and equation. The equation is ASK(t) =
> >> s(t)*sin(2*pi*f*t). I assume s(t) is the baseband signal and
> >> sin(2*pi*f*t) is the carrier frequency.
>
> >> In the image, is it possible for s(t) to have a higher frequency as
> >> sin(2*pi*f*t)? Please explain.
>
> >> Thanks!
>
> >OK I'm probabbly being an idiot here... But is that picture right?
>
> ---
> Yeah.
> ---
>
> >You don't want the carrier to go to zero amplitude do you?  Isn't this
> >like AM radio?
>
> ---
> No; in this case the presence of a carrier denotes a transmission of a
> "1", say, and the length of time the carrier is ON defines how many 1's
> will be transmitted.
>
> Conversely, the absence of a carrier denotes the transmission of a zero
> and the length of time there is no carrier defines how many zeros will
> be transmitted.
>
> JF- Hide quoted text -
>
> - Show quoted text -

Thanks John, That makes sense... sorta. Not the most 'robust' way to
send data. Lose of the carrier means a zero... or that you've just
lost the carrier.

George H.
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