G2 evolution body pack on a body.

Gordo88

Gordo88

Member
I gaffer taped a G2 evolution body pack to talent on friday and noticed a bunch of hum when the metal case touched her skin. I moved it around and sur enough it was sensitive to being placed directly against the skin. I cloth bagged the wireless TX and it solved the problem.

Have wondered ever since.....How could a body pack transmitter be sensitive to a body.

Any takers.

Thanks

Gordo
 
Its almost certainly due to the lack of CMR (common mode rejection) at the front end of the transmitter. Essentially, this is a single ended mic pre, so any common conduction paths (like your talent) can cause a coupling path to the pre. The person has much more area than the transmitter, so their capacitive coupling to the environment is much greater and the induced pickup is also much greater.
 
OK, sorry, let me try again. The Electrical Engineer in me sometimes bubbles up to the surface.

CMR or Common Mode Rejection is the benefit that a balanced input offers (its not just to get a cool XLR connector).

A balanced input has the ability to reject signals that are common to their differential inputs. An unbalanced input lacks any CMR as its path is common to the internal ground reference (which is almost certainly also the body of the transmitter). When this common (local circuit ground) is connected to a source of noise, the lack of rejection causes the noise to become part of the signal.

The human body has a much bigger area than the body of the transmitter so with more area it couples (capacitive like in a capacitor) the environmental noise (electrical noise) at a much higher level.

Let me know where you are not following this and I can elaborate in greater detail if you are still curious.
 
Translation: Organic tissue is mildly conductive, (its the salt content), and when in close enough proximity to a non-shielded signal will couple to and affect that signal.

Benefit: Back in the rabbit ears days of early TV. Get your kid to touch the antenna and move their body around to improve reception. The wildest most uncomfortable position always produces the best picture on the set.
 
The 500 G2 comes with a cool little case that fits it like a glove... I never tested how much difference it makes... now I might give it a go.

This past week we used the G2 a lot and one guy insisted on repositioning the thing... he kept doing odd stuff like coiling up the mic cord and then putting the body pack in some other location... everytime I got comfortable with the system it started acting funny and sure enough he moved or changed something again.

Talent is funny.
 
Thanks muse for a most insightful response, I guess where I have problems with this is....if you were working with senni designing a body pack transmitter, wouldnt this be fairly high on the list of stuff to watch out for??

Maybe it's the spock in me.....

I am slowly coming to the conclusion that the geers who buold this stuff dont actually use it. (case in point the P2 cards)

Gordo
 
I've had G2 packs touching skin many times (usually small of the back or hooked to a bra) and I've never had any problems. Sounds like your unit should go back to the factory for a checkup.

Phil
 
Gordo,

Think of it like your talent just had that spark of animal magnetism after you fondled her skin.

Ken :D
 
Thanks all

Thanks all

Yes, I may take it in for a tuneup.

You should have seen it, top hiked up skirt hiked down testing parts of the body for inductive hum.

Had to laugh

Gordo
 
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