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    PC based Oscilloscopes

    I am about to buy a PC based oscilloscope to save money. I tried nscope but it is not available to buy in Amazon, i am trying Pico 2000 series. But as the frequency increases the cost increases. I am trying for 10MHz, i have one clarification before i make a decision, suppose if i want to see the crystal frequency operating at say 70Mhz, i cannot measure it using the scope is understood. But is it possible for me to down convert it using some circuit and measure or some other technique can i use? Please advise.

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    Re: PC based Oscilloscopes

    For frequency measurement you need a frequency counter not an oscilloscope.
    An Oscilloscope draws graphs of voltage against time so you can inspect the shape of a waveform, if you add some kind of shifting or dividing circuit between the source and the 'scope you are looking at the wave shape from that circuit, not the original.

    Brian.
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    Re: PC based Oscilloscopes

    Quote Originally Posted by betwixt View Post
    For frequency measurement you need a frequency counter not an oscilloscope.
    An Oscilloscope draws graphs of voltage against time so you can inspect the shape of a waveform, if you add some kind of shifting or dividing circuit between the source and the 'scope you are looking at the wave shape from that circuit, not the original.
    Brian.
    I am sorry i mean to say i want to see the waveform which may be at 100MHz which is more than the PC based oscilloscope capability. How to overcome this?



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    Re: PC based Oscilloscopes

    High frequencies are a problem for PC based scopes because there is no mechanism that can send very fast samples for storage and display. Bear in mind that to display the shape of a waveform at 100MHz you need to sample much faster so the shape can be reconstructed later. For example, if you wanted to take 10 samples per cycle your sampling speed would be 1 gigasamples per second. With current technology it isn't feasible to digitize and display in real time so storage within the scope is needed followed by a slower transfer to the PC using USB. It gets very expensive!

    The only feasible way to lower the sampling speed is to synchronize the sampling to the frequency then take samples from consecutive cycles. For example, if you sample 10 times from a 100MHz signal you take sample 1 from the first cycle, sample 2 slightly later in the second sample, sample 3 slightly later in the third cycle and so on. The problem is that although you can observe higher frequencies, you lose the ability to see changes in the wave shape on a cycle by cycle basis.

    I'm afraid there is no low cost alternative to a dedicated instrument.

    Brian.
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    Re: PC based Oscilloscopes

    Quote Originally Posted by electronicsman View Post
    I am about to buy a PC based oscilloscope to save money. I tried nscope but it is not available to buy in Amazon, i am trying Pico 2000 series. But as the frequency increases the cost increases. I am trying for 10MHz, i have one clarification before i make a decision, suppose if i want to see the crystal frequency operating at say 70Mhz, i cannot measure it using the scope is understood. But is it possible for me to down convert it using some circuit and measure or some other technique can i use? Please advise.
    Hi electronicsman!

    I got myself an 20 year old professional FLUKE 4-channel 200MHz digital storage scope off ebay for just around €300 including shipping, it beats any pc-based scope in that price range any given day. That would be my suggestion, look for second hand, especially those with CRT screen.


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