Author Topic: Need for a signal generator  (Read 1338 times)

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Offline akis

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Need for a signal generator
« on: March 19, 2013, 06:26:29 PM »
I have an old, analogue tone generator which produces a tone at a certain frequency and a certain amplitude. When I am running tests I can see what's happening in one frequency but not in conjunction with others.

For the projects I am experimenting with I would want it to create more than one frequencies (maybe up to 12) at a separate amplitude each, so I'd be looking for 12 separate knobs for amplitude control and 12 separate knobs for frequency. Of course if it were digital you'd have "multifunction" buttons.

An additional feature would be the ability to vary the *amplitude* on each channel by a certain amount, % wise, like in AM transmission,  based on a random generator or based on a modulating frequency.

An other additional feature would be to vary the *frequency* on each channel around the centre frequency by a certain %, like in FM transmission, based on a random generator or based on an amplitude waveform.
 
Eg I could say :

 channel 1: base F=100Hz, A=1V pk, sine
 channel 2: base F=1KHz, A=0.1V pk, sine, FM mod: 5%, random generator.
 channel 3: base F=5KHz, A=1V pk, sine, AM mod: 10%, random generator.

Does such a tool already exist?

Offline jpb

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Re: Need for a signal generator
« Reply #1 on: March 19, 2013, 08:37:41 PM »
You don't say if you want separate channels or separate tones on the same channel.

You don't say anything about budget.

Cheaper signal/function/arb generators are generally one or two channel. There are multi-channel instruments available but they are very expensive and designed for much higher frequencies generally than you need.

The Rigol DG4062 has a harmonic function so you can set the harmonics separately on the same channel. It also has two channels. I don't own one so have never used this feature.
It would also be less simple than the analog arrangements of buttons that you envisage.

Here is a paper published on using a graphics card for multi-channel output, each colour channel is used as a separate output and by using multi-monitor cards it is possible to get a lot of channels very cheaply.
http://cds.cern.ch/record/1235884?ln=en

Another thought is to use pc sound cards.

Offline grumpydoc

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Re: Need for a signal generator
« Reply #2 on: March 19, 2013, 08:59:12 PM »
Quote
Another thought is to use pc sound cards.

I was also going to suggest this - along with a decent audio editing program.

Online PA0PBZ

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Re: Need for a signal generator
« Reply #3 on: March 19, 2013, 09:02:57 PM »
Yes, should be easy to do on a pc.

A quick search turned up this: http://www.nch.com.au/tonegen/index.html
I have not downloaded or tested it but maybe it is useful:

 - Sound generator supports frequencies from 1Hz to 22kHz
 - Simultaneous tone generation of up to 16 tones at once

Otherwise it wouldn't be too difficult to program it yourself.

Offline akis

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Re: Need for a signal generator
« Reply #4 on: March 19, 2013, 11:14:01 PM »
Should have thought about the PC and its sound chips - but I was thinking of a bech top instrument to replace my current signal generator. I suppose one of those 200 UK pounds tiny laptops could be used and it could do much more than that - up to 20KHz.

Offline jpb

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Re: Need for a signal generator
« Reply #5 on: March 19, 2013, 11:52:08 PM »
Should have thought about the PC and its sound chips - but I was thinking of a bech top instrument to replace my current signal generator. I suppose one of those 200 UK pounds tiny laptops could be used and it could do much more than that - up to 20KHz.

If you have the space, I'd use a desktop rather than a laptop. You can use cheaper internal sound cards rather than having to rely on external usb ones. Desktops are also cheaper (for equivalent power) than a laptop and if you get a tower unit it can sit on the floor rather than taking up bench pace.

Online nctnico

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Re: Need for a signal generator
« Reply #6 on: March 20, 2013, 12:12:02 AM »
If you are going to spend that much money better get a 'real' signal generator.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.

Offline Telstar

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Re: Need for a signal generator
« Reply #7 on: March 20, 2013, 02:17:38 AM »
You can get a good used function generator for 50-100 quids. A little more for a crappy new DDS (Victor, Atten etc).

Offline jpb

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Re: Need for a signal generator
« Reply #8 on: March 20, 2013, 02:26:09 AM »
If you are going to spend that much money better get a 'real' signal generator.
But the OP wants multiple channels which would need multiple or expensive signal generators. Aside from the cost, 6 two-channel signal generators is going to take up a lot of bench space!

Alternatively if it is just 12 separate signals on the same channel then an arbitrary waveform generator could be used. If the tones are all harmonics then the Rigol allows this but all these solutions are more complicated than having 12 separate knobs.

12 cheap audio generators (perhaps just circuit boards) and a sound-desk type mixer might do the job.
« Last Edit: March 20, 2013, 02:30:05 AM by jpb »

Online nctnico

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Re: Need for a signal generator
« Reply #9 on: March 20, 2013, 04:25:00 AM »
Hmm. I read past that. In that case several USB audio interfaces and the tone generation software mentioned before may do the trick. The biggest problem is that they are not synchronised so the phase relation between the signals isn't fixed.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.

Offline akis

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Re: Need for a signal generator
« Reply #10 on: March 20, 2013, 05:54:13 AM »
If the standard sound chips found on modern day laptops and PCs can actually play these tones (up to 20KHz) and can be controlled from a nice software interface then the idea of a tiny little laptop on the bench is not that bad?

Online nctnico

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Re: Need for a signal generator
« Reply #11 on: March 20, 2013, 06:02:06 AM »
Most modern soundcards are able to use 192kHz as a sampling rate.  I wouldn't dare to predict the actual bandwidth but it should be way past 20kHz.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.

Online PA0PBZ

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Re: Need for a signal generator
« Reply #12 on: March 20, 2013, 06:51:59 AM »
Hmm. I read past that. In that case several USB audio interfaces and the tone generation software mentioned before may do the trick. The biggest problem is that they are not synchronised so the phase relation between the signals isn't fixed.

You don't need several audio interfaces, all you need is the sum of the different signals sent to the audio output. Also, phase relation is done in software, the only thing is to watch out for phase differences in the audio device for different frequencies, but that is easy to calibrate.



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