can anyone explain the ohm symbol after the mv on this scope?

[mkz]

Hi

See the pic.

Is this something to be concerned about if wanting to buy this scope? all tests passed, but I see an Ohm symbol after the four channels  mv at the bottom, and not all are the same value (nothing connected on any of the 4 channels)


thanks

[ataradov]

I think it might be showing 50 Ohm termination on the input. In any case it is not a concern for the purchase. The same symbol is present on screenshots in the user manual.

[w2aew]

I think it might be showing 50 Ohm termination on the input. In any case it is not a concern for the purchase. The same symbol is present on screenshots in the user manual.

Yes indeed, the ohm symbol after the vertical scale value DOES indicate that the channel has the 50 ohm termination engaged.  You may also sometimes see a "BW" which would indicate that the user turned on the low-pass filter (usually 20MHz) on that channel.

[jwet]

This indicates that the 50 ohm termination is active on the channel.  You should be able to turn the terminator off and on for any channel.  Note also that when the terminator is active, the input range is limited to about 5v on most scopes, this would be .5W dissipation of the terminator.  In very basic term (no flames from experts please and forgive me if you know this) A 50 ohm termination is used to make high frequency measurements without causing reflections in cabling.  It becomes important when the wavelength of your setup gets over about 10% of a wavelength.  Wavelength in meters is 300/F in megahertz.  At 30 Mhz- a wavelength is 10 meters, if your setup gets to be on the order of a meter, you'll start seeing transmission line effects.  At very high frequencies into the microwave range, everything has to be terminated and run in transmission line type structures to control impedances and get reliable results.  Turn if off.

[Wallace Gasiewicz]

Essentially when in 50 ohm input mode, consider the scope a "Load" and don't put anything into it that you would not put into a very small load.
Here is one example:    You can use this setting to check the 50 ohm outputs of things like signal generators, you will get the correct voltage reading on your scope that corresponds to the dBm or microwatt output of your signal generator. As always E=IR and R in this case is 50.