131st AES Convention Observations

Re: 131st AES Convention Observations

Maybe this is the perfect time to bring up an issue that I've been meaning to bring up for a long time now. Is it me or do the UR1 bodypacks (and likely handhelds as well) suffer greater intermod problems than the old U1 transmitters? I've found that they do bad things when I put them close to each other. I don't recall the older ones being so touchy.
 
Re: 131st AES Convention Observations

Jason Lavoie said:
that sounds reasonable, but it still surprises me that this came out of nowhere without years of people talking about it as the holy grail that was unreachable yet.. just waiting for better ICs or something like that..
if they've managed this via some patented process other mfrs could be left in the dust.
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And . . .

John Roberts said:
I am not experienced in that technology but in general breakthroughs in device technology are often driven by consumer electronics and then filters down into more professional applications. I don't take the trade journals anymore, but I vaguely recall hearing something about a new IC technology developed to make low cost satellite receivers for GPS, that delivers a huge increase in gain bandwidth product for cheap ICs. This may fall out of that, or may just be a new higher voltage process that allows for more signal headroom through conventional circuits. If there is a patent involved, you can easily read the patent to find out.
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Let's remember that our RF usage within the world of entertainment is an insiginifcant market application compared to cellular/PCS and satellite services. They've suffered severe performance degradation due to IMD from both saturation and mixing for well over two decades. As such, there are now devices and components in the supply chain with very high linearity, IP3 (saturation point) and low noise specifications. Further, over the past ten years the phenomenon of passive IMD ("PIM") (IMD occurring in passive components) has been identified and studied, and products designed and built specifically for low PIM performance have been on the market for the last few years. None of these advanced design and manufacturing processes (and thus the final products) are cheap so it's only after several years of production has the economies of scale permitted adoption by the smaller RF players.

Shure has [not so] simply taken present day knowledge and manufacturing capabilities and applied it to the Axient series (at an added cost), thus one would expect it to perform better than a 12 year old design (the UHF-R).
 
Re: 131st AES Convention Observations

Shure has [not so] simply taken present day knowledge and manufacturing capabilities and applied it to the Axient series (at an added cost), thus one would expect it to perform better than a 12 year old design (the UHF-R)
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Didn't UHF-R hit the market during the end of 2005?
 
Drew. I have not experienced the issues you refer to with UR. Are you transmitting at 10mw an using passive paddles or at least setting the active paddles to the 3dB setting? I see many more issues with folks setting the packs to high power and over driving the receivers with that and the antennas on high gain. I routinely use 8-24 channels of UR with btr800 in the room and ulx nearby in breakouts with few issues.
 
Re: 131st AES Convention Observations

I normally use normal power (10mw) and either stock whips or a combination of passive paddles and whips for exactly the reason you state. Sometimes I end up with the Shure active paddles but almost always run them @ +3. Henry has emphasized over the years (and I've been listening) that over-driving the receiver is a common issue and that generally the only reason to use a lot of gain on an active antenna is to overcome a lossy cable. Using high power on the transmitter is also often an unnecessary thing, especially in the distances that I normally work (<120'). I also generally follow the rule of setting all the mics in the Shure prescribed groups. But let me clarify the "issue". I often see a strong signal on an unused mic receiver when I have a couple or more transmitters in close physical proximity (6"?) to each other and within 10-15 feet of the receivers.

I had some issues with a rack of receivers in Detroit once where I had drop outs and whirlybirds despite all mics being UR and set to the same group (and clean RF meters when all transmitters were off). Between sessions I went through all 10 mics and tested various combinations of transmitters on and off (with all transmitters over 30' away from the antennas). After finding the problematic combinations I switched some frequencies (to other open numbers in the group) and had no issues from then on. I may have had some bad kit that caused those problems but I have adopted this test into my normal routine when using more than a few mics and I often find a few combinations that really seem to peg the meters. So, I find myself concerned about my lav mics (on-stage 30+ feet away) when I have a pile of Q&A mics on my tech table right next to the receivers/antennas.

Now, I'm not literate enough about RF to know where exactly this issue is happening but I do realize that there is a real world limit wrt transmitter power and proximity to the antennae. I'm also aware of intermod issues in the transmitters themselves. BTW, just what is being shown in the graphs that Bennett posted? Also, I'm curious why the single Axient shows about 15db less level than the 2 peaks in the graph of 2 Axient transmitters.
 
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Re: 131st AES Convention Observations

I was curious if you were meaning to imply that the UHF-R was basically the same design as it's predecessor since I think it's been about 12-13 years since it was introduced. I see now that you mean that it's been a pretty long time since R&D began on UHF-R.
 
Drew I don't pay any attention to groups and channels. Where did you learn this? I have heard a few techs particularly in rock and roll say this. I have to say I have never seen wwb generate a coordination with all channels from the same group. Typically they are all over the place. I do not use the on board built in coordination function inside the hardware. I was burned early on using the hardware coordination back when we first got 16 channels of uhfr at Show Systems. In a wwb coordination you can choose more freqs, standard, or more robust. More freqs looks at 2 transmitter 3rds like the hardware does. More robust avoids the worst case imd caused by 3 transmitters up to 7ths or 9ths (I don't remember). I use the more robust coordination whenever possible. I only resort to more freqs or standard when I'm zoning a bunch of systems for breakout rooms in which case I still spread the frequencies in a given room out a bit and put the frequencies that would be in the spaces between in another room to get some distance. I use the hardware or the win radio to scan within wwb. I very seldomly find 3 transmitter imd issues using more robust. I find these by piling up the transmitters and turning them off one at a time. If the signal doesn't completely go away then there is imd. Usually the problem transmitters can be found by turning one more off at a time until the contributing units are found. Usually just separating them a few feet solves the issue but I like to be aware of the potential for problems. If I can change a freq, I do but if not I don't worry too much. Even when double micing I will tend to separate the packs. Also during the show all packs that are not used are off and all packs that are going to be used soon by still in rf land are separated. A common trick is to shield them with tin foil lined boxes but I don't find that necessary. I also lock the units, switch them off and pop the batteries out and back in. When it's time to turn them on they are already locked. The common practice of burning your rf all day and night to save the frequencies doesn't work. It doesn't take into account the imd caused by the idiots in the hotel that just randomly choose frequencies based on the Rf level on the LCD screen. I have found this method to work well and I carry my only switches and routers because about 50%of the racks don't have any networking set up in the first place.

I am working with Bexal's top gun this week. Their sop is to use ias to coordinate freqs then use a spectrum analyzer on site to find any unknown issues. Ones the final freqs are chosen all the normal testing is done just as I described. It's always good to coordinate spare freqs so you can make a change without having to start from scratch. All of this applies to pretty much any wireless but works well with uhfr. Other units and manufacturers may have more problems with outside interference or less happy transmitters. The basic sop still applies though. I am not a fan of mixing rf systems particularly in the same general band split. The distortion in one manufacturers transmitter may cause problems in another manufacturers reciever. I too know just enough to be dangerous but rf has been a hobby for me since I was a kid so I really enjoy learning more about it.
 
Re: 131st AES Convention Observations

harrybrilljr said:
Drew I don't pay any attention to groups and channels. Where did you learn this? I have heard a few techs particularly in rock and roll say this. I have to say I have never seen wwb generate a coordination with all channels from the same group.
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I couldn't find it on their website or in the manual in a quick search, but I've heard it right from the horse's mouth. the whole point of the groups is that theoretically if you use channels that are all in the same group they are coordinated to avoid IMD problems.
that's why (on the ULX at least) there's a group scan function that looks for the group with the most open channels. this makes a great starting point for someone who doesn't have a scanner or prediction software

of course, the group scan doesn't do any math, nor any scanning (other than that group's frequencies) so Drew's problem could easily be from a nearby TV transmission creating IMD with transmitter A that lands on Frequency B. with transmitter B off the receiver ignores the noise because there is no pilot tone. both transmitters on and you'd hear the artifacts, turn A off and the problems go away as well. move away from the receivers and the IMD is less significant..

so obviously the groups aren't flawless, just a good starting point for a small system but if you're setting up more than a half dozen channels its probably best to get some software and a scanner.

Jason
 
Re: 131st AES Convention Observations

It does appear to be a largely un-documented 'feature' but here's a grab from the UHF-R manual. I too avoid the in-hardware scan functions as it seems to me that it's missing some pieces of the puzzle when it scans and tells you what to use. But, I generally don't use WWB either (simply not enough time or concern from those in charge). Of course, I rarely need to manage more than a dozen channels at a time and when I have I've never been bit hard with RF mic problems. (With this attitude it's no wonder I haven't gone Varsity. :?~:-?~:???:)

Shure Groups.png
 
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