Blackmagic Forum

We just recently switched our wireless microphones to the new freq window and discovered RF interference that we have traced to our BM miniconverter Analog to SDI2 box. Our microphones broadcast in the 470-506 MHz range and pick up RF interference on all frequencies. The interference is enough to cause the mics to cut out intermittently which is obviously not acceptable. We record video with a Sony HVR-Z1U Camera to be processed live. Audio is processed through a Berringer X32 Board. Audio and video are combined in the BM miniconverter Analog to SDI2 box. Signal is outputted to post processing through 2 SDI cables (for redundancy).

RF Interference exists when video input is RGB composite or S-Video.
RF Interference is reduced but not enough for the mics to function properly when using only 1 SDI output (which we can do, the second SDI output is for redundancy only).
NO RF Interference exists when Camera is on but video cables are not connected to BM box.
NO RF Interference exists when Audio Only is processed through BM box.
NO RF Interference exists when Camera is on, Audio is on, Video cables R & B are connected but Green is off. However, there is also no live picture when G cable is disconnected.
RF Interference exists using multiple different cables from Camera to BM box.

Camera on or off makes no difference.
Audio on or off makes no difference.
Once the BM box detects signal on the G video input, the RF interference exists.

We are talking to Shure to see if there is anything we can do with the microphone transmitters or receivers. Does anyone have any ideas for us on the video side of things? Thanks.

Wrap it in tin foil.. But the best way is to separate the wireless audio and any wifi, atem related stuff.

What could be is that there is some feedback running back in the poorly shielded cable of the Sony. That component cable is not really the best The converter is enclosed in a metal box. So that should shield it from radiating interference to the outside. But these kind of things are very hard to pin point without a Spectrum analyzer and a good probe. So you can swing over with the probe and see the interference on the screen of the spectrum analyzer.

We wrapped the video cable with tin foil and moved it as far away from the audio equipment as the cabling would allow. We removed one of the redundant SDI cables. That reduced the RF interference by about 50% (estimate). This weekend we are going to go through all the cabling in and around the tech table and separate all the video, lighting, audio and computer cabling in separate racks. We'll try it on Sunday and see if the reduction is enough for the mics to function properly.

If not, we are going to try moving the microphone receivers to the stage and run the audio through the snake. We won't be able to try that until next week.

Any other comments or thoughts are appreciated.

Hello Tony. I would consider using ferrite cores on cables entering and exiting equipment. This is often used for power supply connections being unbalanced. This may be a simple solution.

I don't have direct experience but some Engineers have suggested 75 ohm terminating unused BNC connections. It's an old school thing (my era) and not completely necessary but will not hurt anything.

Regards, Gary

Thanks Gary. I'll try adding ferrite cores and see if that helps. As you say, It can't hurt.

Here's where we are now. We obtained a spectrum analyzer from a friend and cannot find any significant interference in the frequency range. There is certainly nothing coming from the video equipment or black magic box. The background interference is in the 80-90 dB range and the signal strength of the Shure transmitter is around -55 dB at the tech table. It's a roughly 30dB differential in signal strength to background noise. I'm pretty convinced it's an issue with the microphone receiver. I'm putting it back in Shur's court. Thanks Xtreemtech for the suggestion.

Tony, that would be my guess, the Shure mic transmitter or receiver. What happens when you trun off the wireless setup? Try each bit one at a time, receiver, transmitter, and both, and test the results.
Cheers