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Transmitter to oscilloscope

Discussion in 'Troubleshooting and Repair' started by Jeanguypataterubberboot, Nov 1, 2018.

  1. Jeanguypataterubberboot

    Jeanguypataterubberboot

    40
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    Jul 9, 2013
    Just curious if anyone knows why you can't connect a transmitter directly to an oscilloscope. If the output power is less than 10 watts or so the output voltage is only about 20V. Would this damage the scope in any way?

    PV
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
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    Jan 21, 2010
    yeah. If your scope is set for a 50 ohm impedance, the 50 ohm resistor is probably only rated for 1/2W

    If there is no load on the transmitter output, the voltage may be far higher.

    Even if it is connected to an antenna, impedance mismatches can cause standing waves which will result in the voltage varying along the conductor yielding higher (or lower) voltages than expected.
     
  3. davenn

    davenn Moderator

    13,319
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    Sep 5, 2009

    the real question is why do you want to do this ? :)
    what are you wanting to see ?
     
  4. Jeanguypataterubberboot

    Jeanguypataterubberboot

    40
    2
    Jul 9, 2013
    Thanks guys. I don't really need to do it I was just curious as I had heard it was a bad idea but I knew the scope can take some voltage and didn't know if there was something I was missing but didn't want to get bored and try it and damage my scope. I can't afford another one. I guess it's like spectrum analyzers in that respect.(which I don't own)

    Thanks for the input guys.

    PV
     
    davenn likes this.
  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Actually, with a conventional cathode ray tube (CRT) that has electrostatic deflection plates, you can.

    Back in the day... and believe it or not this was waaay before my time... Hams and broadcast engineers would connect their (suitably attenuated) transmitter outputs directly to the vertical deflection plates of oscilloscopes, bypassing the vertical deflection amplifiers, to monitor AM modulation percentage. Over-modulation causes signal "splatter" across the spectrum and must be avoided with AM transmitters. It was usually a problem with plate modulation when the audio amplification was too high, but could also be a problem with screen modulation if improperly designed circuits were used. After SSB "took over" the amateur radio HF bands, AM almost disappeared except for a few die-hard holdouts who still insist on using it today. AM does sound better than SSB on most receivers.

    I don't know anyone who would even think of doing this today, because most modern oscilloscopes don't even have vertical deflection plates... or any deflection plates at all... just liquid crystal displays.
     
  6. Jeanguypataterubberboot

    Jeanguypataterubberboot

    40
    2
    Jul 9, 2013
    Thanks for the reply. Today’s equipment is more advanced but it can’t take a beating like the older technology.
     
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