Hi,

I'm placing my oscilloscope probe tip over a singled end of a CAN bus line with a little meander shaped bodge wire at the end.

I expected to read spikes with inductive pick up but I'm getting square waves. I thought maybe I was capacitively coupled so I tried to change the orientation and the signal falls away like I would expect from inductive pick up.

If I am really doing inductive pick up I am confused why I'm getting a square wave, will an oscilloscope probe act as a passive integrator. Even so I would not expect it to be such a perfect square. Shape works if it's capacitively coupled though...

What do you think, I need to know if the oscilloscope probe lead is causing this and why but I don't know how to figure this out.

Scope is Tenma 72-8710A with its standard probe.

 

Picture of what you have and the traces would be nice.
Your normal electric (capacitive E) and magnetic (inductive H) near field probes for a scope look like this. The loop is the magnetic field probe type. A circuit generates both but not necessarily at the same relative levels in every orientation.

https://www.allaboutcircuits.com/te...-probes-and-their-use-in-emc-troubleshooting/

 

True it's both. To answer my own question capacitive coupling is dominating the signal I'm reading.

Wasn't really worth asking sorry.

 

True it's both. To answer my own question capacitive coupling is dominating the signal I'm reading.

Wasn't really worth asking sorry.

Always worth asking a good question. With this sort of thing it's better to look at it using a fields in space prospective. The circuit theory intuition of discrete components fails to provide a good path to learning here.

 

What you will see with an open probe on a high gain scope channel may not be at all what is expected. A portion of that result often comes from capacitive coupling to a signal that is not expected. What is important is to always verify that what you see is actually what you are attempting to see. And not claiming a new discovery until you have verified it.