Strange RF problem.

[Npoberaj]

So I ve been using, a Lectro MM400C Transmitter w/b6 mic and a 411 receiver. I am also working deep inside a prison walls so outside RF shouldn't really be the problem. Anyways we would be doing a sit down interview so I would be pretty close to the subject and everything would be working fine and all of a sudden I would see the RF bar on the 411 drop low and i would get a "hit" or a his on my wireless. And then all of a sudden everything would be back to normal working condition. Has anyone experienced anything like this before or might now the reason behind it? I should also mention I am going from my bag to the camera via zaxcom stereo.

Thanks,

Nejc P

[hemmerlinj]

You're in a prison, which will most likely have a lot of metal, which could be causing some rf reflections that could be causing the problem.  Just an idea.

J. Hemmerlin

[Npoberaj]

I thought of that, but then why would the signal be totally fine for 30min and than go bad for a split second and then become good again. This has happened a few times now over the last few days.

NP

[hemmerlinj]

Could also be the walkies that the guards are using.  Maybe some type of wireless system being implemented.  Possibly something to do with locking mechanisms for the doors.  Prisons are like small cities.  Anything is possible.  Have you tried a different freq?  Have you tried a freq that is on the coordination chart?  Lots of factors.  I've had similar things happen in places that you would never expect their to be a problem.

J. Hemmerlin

[cmassey]

What freq. is the Lectrosonics on?  Sounds like some kind of stray RF inside the prison...guard walking by that talks on his walkie-talkie...maybe a perimeter alarm system that samples every half hour or so...a sweep of a detector down the hall.  Just ideas...if you are sitting down and stationary, put a cabled lav out there.  I know, obvious solution, I am sure you thought of.

cleve

[Npoberaj]

Hey, the lectro is blk 26. Zaxcom 21.  I think you guys are both right its just probably something in the prison system. I was just seeing if there might be something else like a faulty transmitter. And yes I definitely need to get a wired mic its crazy that I dont have one with me.

Thanks for the help,

Nejc P

[ProSound]

I carry two Ambient Eumel with me all the time quickly makes anything a wired mic. Saved me a few times

http://www.trewaudio.com/store/product.php?productid=268&cat=34&page=1

[Marc Wielage]

I carry two Ambient Eumel with me all the time quickly makes anything a wired mic. Saved me a few times.

The guys at Oscar Sound Tech have a similar adapter that will take any TA5 wireless mike connection and turn it into an XLR phantom plug:

http://www.oscarsoundtech.com/

The Oscar product is very well-made and much lower-priced than the Ambient. Note that you'll need to tell them at the time of the order whether you need "compatible" Lectrosonics wiring or servo-bias wiring. I agree, these will save you if you run into major killer RF problems, provided you can get a wire to the actors.

A couple of years ago, I ran into a similar situation in downtown LA where I did a quick block scan and saw a solid black brick on Block 21 -- scary interference. I think this was within a block of the phone company, so there might have been some weird RF just in that area. We wound up just putting the receiver about 8 feet away from the actor, just out of camera range, and it worked fine.

--Marc W.

[Paul Graff]

I remind you guys that the OP is using a MM400C transmitter which is not wired TA5. I still have 3 hardwired Sanken lavs, but nothing that converts my 14 WP connector terminated lavs into hardwired mics. If anyone has located and used such an item I would love to hear about it. Those three hardwired COS-11s have TA5 breakaways, but I have no TA5 wired transmitters. I just keep them as hardwired lavs.

As to the strange RF problem, I concur with the theories presented, but you don't mention if this has happened on different transmitters or receivers (assuming you have more than one Block 26 system). I had a bad 411A that had a similar, very intermittent problem (also Block 26, coincidentally) and Lectro repaired it under warranty. It wouldn't fail for them, but they found some part pressing against something it shouldn't have and replaced it. No problems since.

PG

[Andy P]

The DPA lavs with their micro-adaptors could save the day in these situations, from Lemo to XLR in seconds. Sorted.

[BVS]

I think you'll find the answer is an RF blocker that is now installed in most prisons to stop cellphones being used by prisoners...I monitored this over 5 days and noticed that in certain areas there would be windows of time when it was not working and then half an hour later would start again...in some areas where the prisoners' cells were,there was a total RF block all the time..but in other areas around the warders rest rooms the coverage was variable...you can easily spot the RF blocking transmitters as they run a wire in a big loop around the fence perimeter...the same as running a loop thru an amplifier to give coverage for multiple receivers..when you step outside the perimeter,the coverage is back...

BVS

[Derek H]

Hey this is interesting because I had a similar momentary rf problem recently.

My situation was this:

Zax block 21 hop (1st gen with filtered antenna)

Block 26 (approx) sennheiser sk50 wireless Mic

Sanken cos11d's

I was also filming in a jail (not a prison tho) but did not encounter any rf jammer.

A few times (say 3 times in 9 weeks)  I had unexplained dropouts on my b26 channel.  All of a sudden the channel would mute....  and then come back after a few seconds of me panicking and thinking the battery had died. 

My guess is either some weird anomaly between Zax b21 and b26 radios OR some kind of wacky rf burst from the police radios.  I'm leaning towards the latter.