RF Query From The Field

C

Caley Monahon-Ward

Freshman
Aug 17, 2012
3
0
1
I am in the midst of tech for a theatre gig going up Friday. I've had some RF problems and think I have a diagnosis, but wanted to run it by the peanut gallery... Or even better, an expert or two.

I have a 10ch rental system comprised of a mix of Sennheiser SK500 and SK100 transmitters and Evo 100 and 500 G3 receivers across the A and G bands. The freqs I have are shop-coordinated and all clear when transmitters are powered down. A pair of what I believe are Sennheiser 12AD active LDPA antennas and three ASA1 splitters. My antennas are in a wing about 8' off the ground on sidelight booms. 25' cables of something beefy -- maybe PWS 9046? Performers are generally 5-30 feet from the antennas but I'll need probably 60' of reach for one scene (I'll have line of sight to at least one antenna for that -- the best I could do). I'm getting inconsistent reception range and occasional dropouts or hits. When my A2 walked the room with a single channel powered on we had vastly better reception than when performers are onstage.

Seems like a case of intermod caused by too much RF gain, right? Should I demand passive paddles?

Tomorrow I'll try subbing in passive omnis to see if that clears up. Not sure I'll get the range I need with omnis, though. I also have the option of lowering the TX power on the SK500s, which are about 2/3s of the TXs I have. Is a mixed-power fleet of bodypacks asking for trouble?

I'd appreciate any insight.
 
Last edited:
Re: RF Query From The Field

If it is an intermod problem, every dB you reduce the offending signal by will reduce the level of the intermod products by 3dB.

Pull the paddles off and replace them with straightened paperclips. Or just lay the paddles on the floor. Problem reduced? Too much signal, possibly leading to intermod was the problem.
 
Re: RF Query From The Field

The last time I had a “shop set frequency coordination” it did not work on site. Since then I have taken the responsibility on myself and I scan and coordinate for each location. I do some musical in 2 different parts of the same town and have never had one locations setting test as being ok in the other location. There are a few other things going on between the 2 places and one of these days I am going to make a worse case configuration to see if I can find settings that I can use for both places.

Are they using wireless comms in this location?

Are you in the USA? If you are, and have the time, post the zip code and the frequencies the units are presently set for and I will run a frequency coordination and see if anything looks funny.
 
Re: RF Query From The Field

Your problem is that you are using an analog system. ALL analog wireless microphone systems are now obsolete and will absolutely fail in areas where there are large amounts of cell phones accessing the internet. I do commercial AV in the Bay Area (San Francisco Area) and there are no non-digital systems that work for large format sound reinforcement here. Basically, if your microphone system is less than $10,000-- it won't work here. Things are different in the middle of Iowa where there aren't any people or technology, but in densely populated areas, you are out of luck.

FWIW -- One of my fortune 500 clients had 8 Sennheiser 3000 series microphones which refused to work during large meetings and the rep from Sennheiser literally told me: "We currently do not have any products that will work in your area" and returned all the mic systems.

I wish you the best of luck, I have been through your experience many times and the only way to solve it was to eliminate all the analog technology.
 
Re: RF Query From The Field

Thanks for the replies....

Some quick responses:
-Actors underneath the RX antennas is an interesting possibility. I don't think that'd be it this time -- it might have happened on this show but very rarely. And the antennas were about 9-10' off the ground, so the actors wouldn't have been right on top of them. Definitely something to keep in mind in the future, though.
-No RF comms on this show.

Here's a post-show update. Things worked out well ultimately, but I changed multiple things at once so hard to say which solved the problem. I got the shop to send an additional pair of passive paddles to eliminate the passive splitter that was splitting the RF between channels 1-8 and 9-10, separated the two main antennas by another 6 feet or so, scanned manually using the receivers and completely retuned using Wireless Workbench, since I had to retune a couple of channels that were seeing interference and ran out of backup freqs in the list provided from the shop. Despite the freqs being initially clear before I turned on bodypacks on the first couple of days of my tech, I did encounter some interference -- some of it strong enough to defeat the squelch -- on later days. So it's possible that some of the problems I had were hits from outside sources that weren't initially active. The theater is a block away from a busy NYPD and NYFD station -- I suppose there might be some intermittent out of band RF from their radios. Or who knows what else.

Subbing in some passive whip antennas did not improve things, so now I don't think overload was the problem. I'm now thinking it was more of a tuning issue, and also the fact that I'm used to working in smaller, more reflective venues. This theater doesn't have a huge stage, but it does have a hollow floor and a fly loft, so I guess there isn't much for the RF to bounce off of.

Time to get a spectrum analyzer, I guess!
 
Re: RF Query From The Field

Tim Duffin said:
Your problem is that you are using an analog system. ALL analog wireless microphone systems are now obsolete and will absolutely fail in areas where there are large amounts of cell phones accessing the internet. I do commercial AV in the Bay Area (San Francisco Area) and there are no non-digital systems that work for large format sound reinforcement here. Basically, if your microphone system is less than $10,000-- it won't work here. Things are different in the middle of Iowa where there aren't any people or technology, but in densely populated areas, you are out of luck.

FWIW -- One of my fortune 500 clients had 8 Sennheiser 3000 series microphones which refused to work during large meetings and the rep from Sennheiser literally told me: "We currently do not have any products that will work in your area" and returned all the mic systems.

I wish you the best of luck, I have been through your experience many times and the only way to solve it was to eliminate all the analog technology.
Click to expand...

That's odd, I recently did a gig at AT&T Park in San Fransisco with 32 analog wireless mics (Shure UHF-R) with no problems at all. IIRC we had 8 H4s, 8 J5s, and 16 G1s.

Any job with more than 2 wireless mics requires some coordination.

Mac
 
Re: RF Query From The Field

mackerr said:
That's odd, I recently did a gig at AT&T Park in San Fransisco with 32 analog wireless mics (Shure UHF-R) with no problems at all. IIRC we had 8 H4s, 8 J5s, and 16 G1s.

Any job with more than 2 wireless mics requires some coordination.

Mac
Click to expand...


Indeed -- I worked at a site in Midtown Manhattan last year that had about 50ch of UHF-R between the main space and various breakout rooms. All coordinated by the in-house AV firm, and with no serious trouble. I'm no guru of wireless, but my understanding is that analog RF is not hopeless by any means. And digital RF is not immune to interference either.

C
 
Top Bottom