RF Interference and Ferrite Cores - audio/video solutions

[htinla]

While looking through the user manual for my HDTV, I stumbled upon a mention of a ferrite core. I wasn't sure what it was, so I did a little research. For those of you that don't know, a ferrite core is that cylindrical attachment that wraps around the ends of certain cables (i.e., USB; A/V cables) and what it does is reduce or eliminate radio frequency interference that is normally present and potentially can degrade the signal coming in/out of a device, such as a camera.

My last shoot had RFI issues concerning audio which I troubleshooted to my use of an external monitor connected to my GH1 via composite cable (the GH1's ferrite core-protected cable). I gathered that the monitor's power cable or the AC power strip it connected to, of which neither was ferrite core-protected, was acting like an antenna and caused the sound of a radio station to leak into my audio (I was using an H4 feeding audio into the GH1's mic input - a padded audio cable was used for connecting, so not a line/mic level issue). One I disconnected the monitor from the camera, the sound problem went away.

So my point is this: does anyone have any knowledge/experience of using ferrite cores and their efficacy as a solution to some of the RFI problems that dslr users confront now and then? The usual advice seems to be about using shielded/balanced cables. But with cameras lacking things like XLR inputs, I'm sure most people like me are using lower quality cabling that invites noise from RFI. Should we make it a point to use ferrite core-protected cables at the very least? Has anyone here solved or attempted to solve an RFI problem by using a ferrite core? If so, can you share the details of your case and how well, or not well, it worked?

The cool thing about ferrite cores is their low price and ease of use - just snap one on any data or power cable. I'm thinking of getting a few of these (available at places like RadioShack) and attaching them to all the cables I connect to my camera, sound equipment, monitors, computer, etc. - basically, I'd like to get a better sense that it's something worth doing.

Thanks!

 

[j1clark@ucsd.edu]

Yes, using baluns aka ferrite core, is quite common in many applications where RF noise could be a problem. The other issue with power supplies and 'grounding' is ground loop caused by connecting equipment 'willynilly' and having shielding and grounds
connected in different places that have a different voltage potentials (yes, 'ground' is not an absolute value...).

Transformers are used to break ground loops, baluns to reduced RF 'pick up'.

But one should always use shielded, balanced cabling for audio.

Since the H4 has XLR imputs, and recording as well, why not use that device in a two system setup, rather than trying to put audio into the GH1. I don't think I'd even think about using the GH1 for a 'recording' device... 'scratch' track to allow for better match up between the camera video and the audio recorded on a H4, or other audio recorder, is what I'd use the GH1 audio for...

 

[htinla]

I agree - double-system sound is the way to go. But for those shoots that aren't so critical, it's convenient to just record straight into the GH1.

I think I'll try a snap-on ferrite bead (core, balun, chokes...hmm these things have lots of names) on the power cable and A/V cables that go into my monitor and see if that tames the RFI problem when connected to my camera. If it works, I just might put chokes on all my cables.