From: peterson_at_d...
Date: 2001-07-17 02:12:39
Stolen from the Yahoo Biofeedback group, a note from Sieg Othmer:
Think of the leads as antennas for whatever electromagnetic radiation
reaches
them. The longer they are, the better "detector" they are for such
radiation.
This is true up to the point where the lead length is one-fourth of
the
wavelength. So for typical lead lengths, we are talking FM band
frequencies
and below. For the best signal quality, keep the leads short. And if
the
leads are long, at least braid them so that the pickup signal becomes
"common-mode."
Another consideration with long leads is increased capacitance. For
the
extremely high input resistances of modern amplifiers, the capacitive
reactance dominates the overall impedance even within the frequency
band of
interest. This means that the balance between leads in terms of
capacitive
reactance is important for maintainance of common-mode rejection at
the
higher frequencies. The best way out of that dilemma is the use of
short
leads, or the use of braiding, because that once again helps to
assure
balance in the capacitive reactance.
Siegfried Othmer, Ph.D.
Chief Scientist, EEG Spectrum International
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:31 BST