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Thursday, September 29, 2016

Video: Sweeping a Filter with a FeelTech Signal Generator and a Rigol Oscilloscope

This short video shows how I used my new FeelTech Signal Generator (90 bucks shipped from China) and my trusty Rigol oscilloscope to display the passband of the filter in my Armand HROish receiver.  Feedback on this test procedure would be appreciated.


  1. Maybe add an AD8307 log amp between the Rigol and the output TIA ? Should flatten out the way the passband looks and also get around the 48 db noise floor on the Rigol.

  2. Excellent! Can the Feeltech provide a sweep-start trigger to the 'scope? AM-diode-detector for amplitude line display? or is that available in the Rigol?

  3. Looks good Bill. Just a couple of very minor points:
    1) If the generator has a Trigger or Sync output, it likely puts out a pulse at the beginning of the frequency sweep. You can use that to trigger the scope, and then you won't have to use such a slow sweep rate and "free run" things like you are now. You'd then be able to synchronize the scope acquisition with the sweep and quickly get your response.
    2) It is good practice to put a 50 ohm termination at the end of the sig gen cable to minimize amplitude variations from the reflections. It doesn't matter in this case since you are sweeping over such a narrow frequency range, there would be very little amplitude change.
    3) In cases where you didn't have the TIA (and the sig gen would see an impedance change vs. frequency), then it would be good practice to insert a 10dB pad between the sig gen and the DUT.

    Great job!

  4. I like it. Granted the AM detector & log amp would be a nice refinement. But your setup clearly shows "no problem" with the filter. So your effort can go into the receiver instead of the test equipment. Good job!

  5. Bill:

    Having build a few superhets around Murata filters, I kept some of the 1980's Murata catalogs around for reference. Will send you a scan so you can compare your results to spec. There was always something cool about those Murata filters. Glad to see your incorporating a vintage part in a new project.

    Chuck, KE5HPY

    1. Thanks but I don't think this is a Murata. It is a Toyo CM455.


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