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From: Martin Trump on 7 Dec 2009 07:55


> Nyquist says you need at least two samples per cycle to adequately
> recover the waveform.

I have to wonder if this thread has gone down a blind alley. As I see it
the OP probably wants just the amplitude of the IF strip's output, not
to reconstruct the waveform. Just a guess.
From: Jim Mack on 7 Dec 2009 08:05
Martin Trump wrote:
>> Nyquist says you need at least two samples per cycle to adequately
>> recover the waveform.
>
> I have to wonder if this thread has gone down a blind alley.

Or just a side street. Wouldn't be the first one.

> As I see it the OP probably wants just the amplitude of the IF
> strip's output...

I'm sure you're right. The question is, how often does he want to read
the amplitude? (-:

--
Jim Mack
Twisted tees at http://www.cafepress.com/2050inc
"We sew confusion"

From: Martin Trump on 7 Dec 2009 08:26

>> As I see it the OP probably wants just the amplitude of the IF
>> strip's output...
>
> I'm sure you're right. The question is, how often does he want to read
> the amplitude? (-:

Good question. Many factors involved but principally the frequency sweep
rate of the i/p. I think better the OP should post again and give some
more details rather than we hypothesize.

Martin
From: MoiInAust on 7 Dec 2009 23:24

"Martin Trump" <martin(a)wmeadow.demon.co.uk> wrote in message
news:oW6Tm.73773$os.65699(a)newsfe25.ams2...
>
>
>> Nyquist says you need at least two samples per cycle to adequately
>> recover the waveform.
>
> I have to wonder if this thread has gone down a blind alley. As I see it
> the OP probably wants just the amplitude of the IF strip's output, not to
> reconstruct the waveform. Just a guess.

Yes, graphing the amplitude against the frequency should give a resonance
curve. Eg frequency 455 KHz +- 20 KHz perhaps gives a curve similar to a
curve of normal distribution. If there is a crystal or mechnical filter the
curve will be much sharper but should be symmetrical if the filter is on
frequency.


From: MoiInAust on 8 Dec 2009 04:19

"MoiInAust" <user(a)user.com> wrote in message
news:4b1dd502$1(a)dnews.tpgi.com.au...
>
> "Martin Trump" <martin(a)wmeadow.demon.co.uk> wrote in message
> news:oW6Tm.73773$os.65699(a)newsfe25.ams2...
>>
>>
>>> Nyquist says you need at least two samples per cycle to adequately
>>> recover the waveform.
>>
>> I have to wonder if this thread has gone down a blind alley. As I see it
>> the OP probably wants just the amplitude of the IF strip's output, not to
>> reconstruct the waveform. Just a guess.
>
> Yes, graphing the amplitude against the frequency should give a resonance
> curve. Eg frequency 455 KHz +- 20 KHz perhaps gives a curve similar to a
> curve of normal distribution. If there is a crystal or mechnical filter
> the curve will be much sharper but should be symmetrical if the filter is
> on frequency.
And to answer the other question, the sweep need only be fat enough to give
a good stable trace on the oscilloscope/screen, say 50 Hz?


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