Interference type issue with Sennheiser G3 kit

[Ty Ford]

The thing about “clear” frequency blocks is that they may or may not be clear.

The interfering signal may be intermittent. So you scan, and in that moment it’s clear. 43 seconds later something changes and you get a hit. You may never get another one on the frequency the rest of the day or you may get one every once in a while.

Even if you jump up a block and find a new frequency that appears clear at the moment you scan it, there may still be intermittent traffic on it as well.

Regards,

Ty Ford
Cow Audio Forum Leader

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[Joe Bressler]

I have noticed in several situations that I will scan for a new list of available frequencies and find that there are several banks with available free channels.

Then i will run into RF interference, scan again, and notice that there are zero banks with any free channels.

Is this explainable? Really starting to think I have a bad kit here with how unreliable these units are. I know that occasionally you have to scan for new frequencies to use especially when changing locations, but I am finding myself with the devices set up properly, in one location, and facing RF hits constantly. It is not practical to switch channels several times during a shoot sometimes.

[Ty Ford]

Hi Joe,

Please go back and read my last response. It answers your question.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford’s Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford’s Blog

[Joe Bressler]

Hey all,

A little update to this story. I have been using the Sennheiser system with the receiver mounted off of the camera (with this setup) with much better results as of the last writing here. I’ve also used other Sennheiser systems with other a7s rigs flawlessly (albeit not mounted to camera) (30 interviews in 3 nights with not one RF hit). I’ve used this system with c300, mounted to camera, no RF hits.

After a call to Sennheiser tech support we determined that my particular camera was acting as an RF antenna that was causing the afore mentioned interference based on this test:

Just camera and cage set up and turned on. Receiver turned on. Receiver exhibits a little bit of RF on the display. When moved away from camera RF goes down and then out completely

Camera, cage, rails, monitor and shotgun mic attached, same behavior only a little more RF is present when the receiver is close to the rig than before.

With the same setup as above, I scanned a new list with the receiver mounted to the camera with squelch on low. No free channels usable.

My question is: are there any a7s users who have had this problem before? Is there a setting on the camera that I can change to stop this from happening (it’s on airplane mode)? Do I need to get a new camera??? This happens regardless of what monitor is bolted to the rig, and I have also noticed strange feedback on sound coming from my rode videomic plugged straight into camera as well.

I want to be able to mount the receiver on or near the camera like I am supposed to be able to and (within reason) not have to worry so much about it!

Thanks for your advice in advance!

[Roger Van duyn]

This is might be slightly off topic, but the last post mentioned an unexpected source of rf interference, his camera. A few days ago while filming a deposition, I ran into a new source of rf interference with my setup. It was intermittent, and weak, but I could hear it through the headphones. I had a hunch it was something in the very close by, coming in and out of range. Probably in the same room.

So I started trying to figure out where it was coming from. All of us had turned off our cell phones. And there was nothing else in the room but me and my gear, the court reporter and her “typing thing” connected to a laptop. The two attorneys, the doctor giving the deposition, and four chairs. Then I heard the faint buzz again, when the doctor’s wrist moved next to the lavalier microphone. Then the next time his wrist got near the mic, it happened again. He was wearing an Apple Watch. I think the watch was trying to connect to his I-phone or something.

When I started working on the footage, the interference wasn’t audible. But it was audible in my headphones.

Lots of new challenges out there.

Roger

[Joe Bressler]

OK check it out. I got to the bottom of the problem but now I don’t know how to solve it.

After systematically taking apart the rig and checking how the receiver behaved after the removal of each individual component I finally got to the last three bits: the camera body, the metabones speedbooster, and the canon 24-105. With all three together there was the same RF behavior as before, but after the lens was removed, the RF dropped off and there was no longer an issue! I’ve also noticed that when the camera is powered on and the lens “engages” there is an RF spike and then it returns to about 1/3-2/3 filled on the display.

Any ideas?

[Ty Ford]

Wow, Roger,

Thanks for bringing this up. So it was in the headphones but had bypassed the actual recording?

How does THAT happen unless the interference was only on the unbalanced headphone circuit?

How could it get there without first hitting the mic input? Was the mic a balanced mic plugged into a balanced input?

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford\’s Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford\’s Blog

[Roger Van duyn]

My wireless kit isn’t the greatest, but it’s been adequate for the type of jobs I do. It has three Azden 35BT UHF transmitters with 310 Receiver and an even older twin (non-diversity) receiver. Like you mentioned, the transmitters all have unbalanced microphone connections.

The receivers have balanced xlr connectors that connect to my mixer, a vintage Shure M-267 I actually repainted a few weeks ago. Then an xlr output from the mixer connects to the camera. So, the sound was probably bleeding through the unbalanced cables themselves? Makes sense. I was about 4 feet away from the doctor. The sound only happened when the watch was a few inches from the mic.

As an aside, I found a funny looking device called a “tripod basket” that Manfrotto used to make years ago when the old video cameras all had separate recorders. It’s the right size for the mixer, and everything mounts on the tripod legs. I have a 4 connection (color coded and number) xlr snake cable coming out the back of the mixer that I connect all the receivers to. Almost all the depositions I’ve filmed have been in small rooms. Once the room was so small that I had to film through the doorway, and I’d just cobbled together the tripod setup the day before.

Here’s how the setup looks:

Roger