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Signal generator and feed through termination

Discussion in 'General Electronics Discussion' started by Bucephalus, Sep 12, 2010.

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  1. Bucephalus


    Apr 3, 2010

    I'm new to electronics and I recently bought an signal generator for my bench.
    I'm reading the manual and it mentions that I have to terminate the coaxial cable into a 50 ohm through-termination.

    It really go into details why. When they say terminated, I'm assuming that I don't put it at the signal generator end of the cable? Or do I? Is this required for me to start using this thing?
    In particular it states this in the context of wanting to achieve an exact square-shaped signal.

    Anybody know about this?

  2. Resqueline


    Jul 31, 2009
    It's about reflection & cable length. If the receiver end of a 50 Ohm cable is left unterminated then hf signals will "bounce" back to the source. Try it out on a 'scope if you have.
    This is more pronounced at higher frequencies (not much to worry about in the audio range) and will therefore affect the edges/flanks of square waves before anything else.
  3. shrtrnd


    Jan 15, 2010
    When you're outputting an AC signal from your generator, the 50 ohm termination (you put it on the output END of the cable from your generator, TO the instrument you're sending the signal to. NOT AT the output of the generator itself), ensures a known constant load on the generator output signal, that the generator circuitry was designed for. So that you get an accurate output. The 50 Ohm feed-thru terminations are readily available, and easy to find. Put the generator output to a DVM with and without the 50 ohm termination, and you'll see the difference. You MUST have the 50 ohm termination to be sure the generator is loaded correctly, to output a consistent (accurate) output. Most scopes nowadays have the 50 ohm load at the scope input already, so you won't need the termination going directly into the scope (just trivia), and a lot of very high end equipment has the 50 ohm termination incorporated into the circuitry of the instrument (Just trivia, to be aware of, when you're making measurements).
    Remember, the 50 Ohm termination is ONLY used for AC output from your generator. You don't use it if your generator outputs a DC signal in other function modes.
    If I wasn't clear, what else do you need to know?
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