signal generator

Discussion in 'General Electronics Chat' started by samjesse, Dec 15, 2009.

  1. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    Hi

    I could either build or buy a signal generator depending on how much pain/price will cost me.

    I am after a good sine wave plus the other standard waves generator. I need it to test an inductance capacitance circuit for resonance. up to 1GHz

    thx
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
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    I would buy. Try ebay.

    Going up to 1GHz will make it expensive. 100MHz cheaper. Price, as always depends on quality.

    Also, you will need measuring equipment to 1GHz - also expensive!
     
  3. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    A precision will probably produce a lower distortion sinewave.
    The circuit you show uses a XR2206.
    This chip uses the triangle signal for creating the sinewave using a "sinewave shaper".
    This will always have some distortion compared to a "true" sinewave generator.

    Greetings,
    Bertus
     
  5. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    Do you recommend a link for a DIY "true" sine wave generator?
    How can I build/buy a "true" sine wave generator?
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Take a look at the attached aplication note from TI.

    Greetings,
    Bertus
     
  7. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    looking around to buy one. I can not find a unit which states "true" sine wave generator. however from ready, I came across a distortion factor.
    what do I look for in order to get a "true" sine wave generator?

    thx
     
  8. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    If you just need to do those resonance tests up to a gig then you're probably better off buying the equipment.

    If your goal is to learn about electronics, reactance, resonance, sine wave generation, distortion and topics like that, then you'd learn a lot by making or even buying that XR-2206 circuit and using it to experiment with lower frequency circuits.

    But if you're serious, it would be worth it to buy a better quality generator than that
    simple board. I'd recommend getting one with a built-in frequency counter, or buying an external frequency counter because it will help make resonance testing so much easier.

    I suspect that "true" is being used to describe sine generator that generates a sine from a sine oscillator, as opposed to a generator that first generates a triangle or sawtooth or square wave, or synthesizes a sine from pulse width modulation, then filters out a fundamental sine signal. I'm not sure that "true" really matters so much, as a reasonable sine can be filtered from just about any source.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    If you really want to get serious about it, then what you need is a network analyzer; most preferably one that has an S-parameter test set either built in, or that comes with it.

    Such items aren't particularly cheap, but are the best way to test such things. With the S-parameter test set, you can see transmitted and reflected energy simultaneously.

    A (big) step down from that is using a spectrum analyzer with a signal generator; you won't see the reflected energy, but transmitted energy is much better than nothing.
    Here's an idea for a cheap 2.4GHz spectrum analyzer:
    http://www.circuitcellar.com/library/print/0406/Armitage-189/index.htm
    $50 in parts for a PC-based 2.4GHz spectrum analyzer is nothing to laugh at.

    Dick Cappels is a member here, and he whipped up this nifty MAX038-based 20MHz sweep/function generator with markers:
    http://www.cappels.org/dproj/functsweep/functionswp.html
    The MAX038 is tough to find nowadays; it's been out of production since around 2003 after some disaster happened to the factory where they were made.
    Futurlec.com apparently still has some in stock, but they're expensive (around $23) and be prepared for them to charge your credit card quickly, and for the parts to take a month or more to arrive.
     
  10. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    I ebayed for that and found it pricey.
    since I have a very high quality 4 channels scope. is there another machine which my scope would complement rather than spend money for some functionality in the S-parameter Network Analyzer which I have in the scope?
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    What 'scope do you have? And what options are installed in it?
     
  12. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    I was not able to find that a Network Analyzer produces "true" sine wave.
    http://en.wikipedia.org/wiki/Network_analyzer_(electrical)

    I need to be able to generate a precision sine wave.
     
  13. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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  14. SgtWookie

    Expert

    Jul 17, 2007
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    A network analyzer has its' own internal oscillator. They generally produce a very pure sinewave at a very constant level, that's swept across the selected range of frequencies.

    Here's another idea for building a vector network analyzer:
    http://n2pk.com/

    Not a particularly easy build, but you could wind up with up to 500MHz if you do a good job on the oscillator. It's a pretty advanced project, and the components are SMT/SMD.

    Your 'scope doesn't have an S-parameter test set - it's just a 4-channel PC-based oscilloscope.
     
  15. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    what do you think of this one here
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    Those are good units; 300kHz to 3GHz - but they are also ancient.

    I see the adapters are missing from the ports. That makes me nervous. Those can be expensive. They are fiddly to connect properly. It's not something you can buy at a local electronics store. If the unit is shipped without the adapters in place, or protective caps on the ports, and they get damaged even slightly, you will have a very expensive repair on your hands.

    The interconnecting cables between the analyzer and the S-parameter test set can be "finicky", meaning intermittent. Sometimes all that's necessary is to remove them and clean the connections with pure isopropyl alcohol and a soft nylon brush.

    It also makes me nervous that he's selling it "AS-IS", without showing that it works.

    While the HP8753B's are actually repairable, you can no longer get replacements for the CRTs. Once the CRT gets too dim to read, you'll either have to figure out how to interface it to an LCD or another type of video output device. It won't be a simple fix. Keep in mind that it was used in a manufacturing environment, daily, for many years.
    [eta]
    Just found this place sells LCD replacement kits for HP8753B's; prices start at only $1,395
    http://www.ntecusa.com/search.cfm?mfrID=240&catID=63
    Expensive, but beats having to junk an otherwise good and usable piece of test gear.

    [eta]
    Don't forget that you'll need proper coax to connect it up with. I prefer to use semi-rigid.

    You should also use 6dB attenuators in the coax from both ports. This helps greatly in reducing errors in your readings.

    You will also need a calibration kit. They're generally available for both 50 Ohm and 75 Ohm. This isn't something you should scrimp on, as if you don't properly calibrate, you will get poor results. A calibration kit consists of an open, a short, a load, and a through connection.
     
    Last edited: Dec 17, 2009
  17. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    Is this able to generate a precision sine wave? would it be software controlled instead of buttons on a box?
     
  18. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    What do you think of this unit off ebay?
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    Why don't you read the technical documentation supplied?
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    If you think you're going to get a perfect sincewave generator for AU$199, I have a bridge for sale that you might be interested in.
     
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