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Frequency detection circuit

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through 06 March, 2006 » Frequency detection circuit « Previous Next »

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Kenon
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Username: Kenon

Post Number: 25
Registered: 09-2005

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Posted on Tuesday, 28 February, 2006 - 02:52 pm:   Edit Post Delete Post Print Post

If the signal is a complex wave.ie.
V=5sin(wt)+ 3sin(3wt) + 2 sin(5wt) volts

Any circuit or method can detect these three frequency such that the magnitude of each frequency is shown on voltmeter?

many thanks!
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Zeitghost
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Username: Zeitghost

Post Number: 76
Registered: 01-2006

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Posted on Tuesday, 28 February, 2006 - 04:51 pm:   Edit Post Delete Post Print Post

Spectrum analyzer?

Selective Level Meter (Hp3586)
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Petelobus
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Username: Petelobus

Post Number: 93
Registered: 06-2005

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Posted on Wednesday, 01 March, 2006 - 08:42 am:   Edit Post Delete Post Print Post

Are the frequencies fixed, and not too high? If so, messy analogue way that would require lots of work, but could be low cost in terms of components, would be a set of sharply tuned bandpass filters feeding precision rectifier circuits. Lots of thought needed to determine right order of filter, and to optimise precision rectifiers. Guess that there is also a cunning Digital Signal Processing (DSP) technique, but thats not really my field. If you only want to do it once, and its a commercial job (rather than hobby/for fun) best trick would be to hire one of the instruments suggested above.

Sure that someone like Pico do software for their computer based scope to turn it into a spectrum analyser.

Ian
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Zeitghost
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Username: Zeitghost

Post Number: 78
Registered: 01-2006

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Posted on Wednesday, 01 March, 2006 - 09:06 am:   Edit Post Delete Post Print Post

Scopes like the Tektronix tds2000 have spectrum analysis software.

Works quite well up to reasonably high frequencies.

(That's 10s of MHz not GHz by the way).
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Epithumia
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Username: Epithumia

Post Number: 181
Registered: 07-2005

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Posted on Wednesday, 01 March, 2006 - 09:20 am:   Edit Post Delete Post Print Post

National's MF10 switched capacitor filter chip is a neat way to build a bandpass filter where the frequency can be easily set and altered.

The filter frequency is set directly by a clock, or by the clock and a resistor ratio.
'Bother,' said the Borg. 'We've assimilated Pooh!'
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Obiwan
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Username: Obiwan

Post Number: 188
Registered: 12-2005

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Posted on Wednesday, 01 March, 2006 - 02:36 pm:   Edit Post Delete Post Print Post

They also made "tone detector" chips, for use in things like DTMF.

Don't know if that would work or not, it's more of a logic output than a quanity that could be measured.

And I would think that a DsPIC (or similar) would work.

A while back I did some work with a Motorola digital signal processor that could do some stuff like that. Would be pretty heavy in the programming though.
May the Force be with (most of) you.....
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Kenon
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Username: Kenon

Post Number: 26
Registered: 09-2005

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Posted on Friday, 03 March, 2006 - 03:25 pm:   Edit Post Delete Post Print Post

Thanks All

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