Unknown noise source when using external mic
 

Hi:

Have a weird problem, I don't know if this belong in this section or in the sound section: I have a Canon XH-A1 with AT-897. It is camera mounted, although the camera mount is not exact fit and I haven't found O-rings or other that I can pad with. The camera is mounted on a tripod.

With the built in mic, I have no problems. But using the AT-897 I get noise from an unidentifiable source. It appears that I pick up some radio, turns out to be a station at 100.10MHz. I cannot hear this source with the naked ear, only on the recording or when using headphones do I hear this, and only when using the external mic.

I made a test: First, the signal is stronger when I have headphones connected, and depends on where the cable is with respect to the camera. The signal I pick up is stronger when the head phone cable is in front of the camera and horizontal. Slightly weaker when cable is vertical. But, it also appears that signal depends on where I am, even if I don't touch the camera, and I still pick it up with head phones disconnected.

I get the strongest signal when I am in front of the camera with head phones, holding the cable horizontal.

Any idea how this noise is picked up?

Thanks, Erik

How close are you to the transmitter?

Might be the result of a poor ground connection or a cold solder joint in the cable or microphone.

Does using phantom or battery power make a difference?

Sorry for the noise on this channel :-) this phenomena appears to be more weird and very local. Moving the camera around in the room, and I no longer pick up the radio, so it appears also to be a particular architectonic problem - I have a noisy spot, and the signal really depends on how close the headphone cable is to the focal point of this spot.

Certainly, there can be a question of lack of grounding, while doing tests at home I use the charger to power the camera. But I think it may also be a question of having properly shielded cables.

Yet, it remains a mystery how the A1 can function as an FM receiver (fine tuning, it appears they are sending on 100.40MHz), how, what should be output only, the headphone jack, can work as an antenna, and why this is only a problem when using an external microphone, this seems to indicate that some circuits are not properly isolated.