Technical note 7
Reference conductors - an illusion
The 'voltage' (counter electro-motive force) that is induced by a signal current between two so-called 'signal references' is equal to the product of the signal current, the loop area between the two conductors and the frequency. The suggestion in much literature of a voltage drop across some mysterious impedance Z is incorrect. The 'voltage' depends on the frequency and on the loop area, so the impedance Z is undefined.
The opposite also occurs: when HF noise flows via a 'reference' conductor, the 'voltage' that is induced in the circuit is not caused by voltage drop across a fictitious impedance Z, but is proportional to the magnetic flux between the signal conductor and the 'reference' conductor, so on the area between the two conductors.
Meter M2 shows a larger voltage than meter M1, although both connect to the same 'references'.