I lost the animal ground connection, not the panel ground connection, and suddenly pick up radio signals in my recordings (in vivo extracellular, tetrodes). I was wondering how this is explained from a circuit point of view.
Also, does it imply that my setup shielding isn't good enough (if animal ground is fine)? Can I still use the animal if I reference from another channel?
Hello Lars,
There are two main aspects in getting the bio-signal corrupted - the system noise and the interference and stray pick-up of unwanted signals (again called as noise).
And so are two key areas we need to address in our experimental setups - 1) Proper Shielding and 2) Proper Grounding.
Keep it in mind that any piece of wire acts as an antenna to pick-up RF signals into your system. Therefore use of properly shielded cables is a must.
Second, you are talking about the GROUND. Are you using something like Farady Cage or is your experimental bed or platform Grounded Properly.
Sometimes even incorrect Ground-Loops DO INTRODUCE noise in the signal. So just pay attention to that!
As far as RF interference you are talking, how sure are you that it is RF from some known radio source? May be you can try some Low-Pass-Filter in your system but I would prefer to call it as EMI rather than RFI.
I hope I tried to address some key areas where you can work out to isolate and address the problem.
Best wishes!
-PRASANNA WAICHAL
If the reference and ground were connected to a common skull screw and the ground wire is broken you could try to fix the wire but if it cannot be fixed and is left loose it effectively becomes an antenna that picks up noise.
Thanks you two for the answers!
@ M Ratner: The referenca and ground were connected to the same skull screw, and yes, one of them broke, hence acting as antenna. This cannot be fixed anymore and I'll pay more attention to protect these wires from physical impact next time.
@ Prasanna Waichal: Regarding the radio noise, I am sure because I can hear the radio playing music. I need the hifh frequency range for my experiments, low-pass is not an option. And this happens even within my (what I previously considered) Faraday Cage. Everything is connected to the same ground, so my suspiicion is that the ground is not clean.
So how do I find out if this is really the case? And more importantly, how can this be fixed?
Cheers, Lars
Hello Lars,
Good to know back from you. If you are sure that it's the local(?) radio station talking to you, well, the LPF I suggested was meant to filter out these RF signals and I believe, you are not interested monitoring those high frequencies in the MHz range where as your biomedical signals would be in the sub-kHz ranges (
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