Is joule thief circuit gets overunity?

[TinselKoala]

The channel BW limit can be set individually for each channel. But as you can see in the scopeshot below, it is the channel WITH bandwidth limit "on" that has the noisier signal, complete with some small positive DC offset.
The channel vertical settings are inside the red box, and the inverse highlighted "B" indicates BWL on.

I've also attached the Atten manual for easy reference.

[poynt99]

Thanks for the info TK.

If the BW limit is already on, then that channel would seem even more suspect to me.

I'll try this with the Tek and see if there is a difference in the apparent noise floor.

[ltseung888]

BW level OFF for both channels.

Noisy channel behavior disappeared.

[TinselKoala]

So now there is excessive noise on Ch2, and there is still a slight DC offset on Ch1.

Both channels, with probes shorted, should be reading a plain, straight, noisefree line, at exactly the level of the channel's baseline indicator.

BW Limit ON should definitely NOT add noise to a grounded channel.

If this is not the case, then there is something wrong somewhere.

[poynt99]

Here are my DPO4054 BW vs. Noise results, with probe shorted and set on 20mV/Div.:

20MHz ~ 600uVrms
250MHz ~ 1000uVrms
500MHz (Full) ~ 1000uVrms

There is a noticeable visible difference (increase) in the noise floor going from a BW of 20MHz to a BW of 250MHz. This should be as expected.

Of the above readings, about 130uV is DC offset.