AC Signal Below Ground

[JLM]

I am familiar with the concept of an AC signal riding above a DC voltage.  In such a case the DC component can be filtered out through a capacitor, or using the AC coupling mode on the scope, in which case the resulting waveform would be an AC signal centered on ground.  I would have thought I would get the same result if the DC component is removed altogether.  But when a sine wave generated by my signal generator is fed directly to my scope, the waveform is entirely BELOW ground, as can be seen in the picture.  Can someone please tell me why that is? 

[Simon]

is the scope calibrated (self calibration) ? are you sure you don't have a DC offset set on the signal generator ? you can have a negative or positive bias

[Jon86]

The signal coming from the function generator probably has a DC offset of just under 1v.

[JLM]

yes, self-calibrated.  I do not think this SG can provide a negative bias

[Jon86]

If it can provide a bias, it's very likely it can also go negative.
Which function gen are you using?

[JLM]

Instek GFG-8020H

[peter.mitchell]

Instek GFG-8020H

Code: [Select]

Features
*Frequency Range : 0.2Hz ~ 2MHz
*Coarse and Fine Tuning
*Waveform : Sine, Triangle, Square, TTL Pulse
*CMOS Output
*Built-In 4 Digits Counter (INT Only)
*Large 0.5" LED Display
*Variable DC Offset Control
*Output Overload Protection
*VCF Input Function


Code: [Select]

DC Offset <-10V to >+10V (<-5V to >+5V into 50? load)


[JLM]

Nice!!  Mystery solved!  You guys are great.  Thanks