Signals of electrodes in B-array appear noisy

[Yaronm]

Hi,

Problem:
After setting up the system (64 electrodes) on a subject, we inspected the online signals from the software panel. All signals belonging to the electrodes in the B-array seemed considerably more noisy than those in the A-array. The noise seemed as high frequency signal added to the EEG signal.

Things we tried to do:
Rechecking the electrode offsets, all seemed ok.
Changing batteries.
Inspecting the blue led on the box (was continuous blue).
Change the B-cable with an alternative B-Cable with have in the lab - problem persists.
All electrodes (A+B) reacted to the subjects facial expressions and thus reflected some real signal.

Does it necessarily imply on a problem in the box? Could it be related to the amount of gel?

We already used this system for several years with no such problem.

Thank you for your help.

[Coen]

Most probably pickup of alternating magnetic (50/60 Hz ?) field by a loop between A cable (with CMS/DRL) and B cable. Bundle the A and B cables as much as possible to minimize the area of the loop between A and B cables.

Best regards, Coen (BioSemi)

[Yaronm]

Coen wrote:
> Most probably pickup of alternating magnetic (50/60 Hz ?) field by a loop
> between A cable (with CMS/DRL) and B cable. Bundle the A and B cables as
> much as possible to minimize the area of the loop between A and B cables.
>
> Best regards, Coen (BioSemi)

Thank you, I will try that.
My intuition is to separate the cables as much as possible. You suggested to bundle the cables. Should I bundle the A and B cables together?

[Coen]

Yes, bundle all cables together.