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Old August 16th, 2006, 10:53 PM   #1
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Bank A, B, C or what?

Looking over the Sennheiser ENG100 G2 product among others. I understand how the banks are divided among Megahertz. What I don't understand is why I should care if all I'm doing is shooting in the US.

There are generally the same UHF TV station signals to avoid coast to coast. The same local gobbedegook crowding the airwaves.

Is one bank "cleaner" from this energy than another? Which bank would YOU choose if shooting in the continental US?

TIA

- Loren
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Old August 17th, 2006, 05:10 AM   #2
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The idea is to pick the bank that has the least number of channels blocked out with interfereing services in the region where you're usually working. Sennheiser has a "frequency finder" page on their website that can be helpful in deciding which frequency blocks are the most open in various areas. Although its accuracy is somewhat limited it's better than nothing. A professional dealer or rental house in the area can also help you decide on the best options. When mixing and matching gear, any transmitters and receivers that need to talk to each other obviously need to cover the same frequency bank.
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Old August 18th, 2006, 04:35 AM   #3
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Thanks, Steve. Got the Sennheiser chart. Still don't know if I'm *generally* safest in one bank over another for US. I generally shoot New England but this January I'll probably shoot west coast. I guess I should be alert to maritime frequencies along with common UHF channels.

I guess I'm wondering if any visitor here has successfully used a single system on both coasts without interference. I do mostly trade show work, and that's an urban setting.

A lot to scope out...

- Loren
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Old August 18th, 2006, 02:10 PM   #4
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I have a "B" band G2 system, bought based on the most open channels in my two home cities. Different cities in our country have different combination and numbers of UHF broadcast stations, and this varies greatly but based mostly on city population.

I do travel a lot and can say I have found open freqs recently in Salt Lake City, Tampa, Jacksonville, Chicago, St. Louis, Kansas City, Los Angeles, Valencia, New York, and Las Vegas. Some cities have more open than others (Big Piney, WY-wide open rf spaces...) but I always manage to find a few out of the 1400+ channels available in the unit.
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Old August 18th, 2006, 03:01 PM   #5
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Buy for the region you are going to operate in the most. You will probably be OK in the rest of the US. The reason for this is that UHF TV stations are not, even in the same metropolitan area, channelized so that they can interfere with one another. Thus even if two adjacent channels are listed as being occupied in a particular area if you are close enough to one that it will interfere, you are probably far enough away from the other that it won't. For example it is unlikely that WMPT (Maryland Public Television) will interfere with you if you are in Washington DC while converesely it is unlikely that WETA (in Northern Virginia) will bother you in Baltimore.

Power falls off very rapidly with distance from the transmitter (square law or 6 dB per doubling of distance) so that, theoretically at least, as long as you are reasonably far from the transmitter and your wireless components are close enough you should be able to work. Of course in r.f. propagation almost anything is possible (such as being interfered with in Philadelphia by a station in New York during "sporadic E" conditions).
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Old August 19th, 2006, 12:11 AM   #6
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AJ, Greg and Steve, most helpful, thank you. I think I'll be looking for a B band set.

- Loren
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Old August 21st, 2006, 07:48 PM   #7
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Answerng my own question, I have found the mother lode. Beautifully laid out charts, state by state, major city by city, from deep within Sennheiser's website.

http://www.sennheiserusa.com/newsite...qfinder-ew.asp

This is *not* a generalized country chart-- it's US, city by city, which is what we need. Just pick your city and determine for yourself whch has the most open air.

I was going to pick up a Bank B Evolution G2 but online seller www.skilex.com sales rep Bobby Ghazi recommended Bank A for optimal air, shooting in Boston, LA, and San Fran. And generally you want to stay away from C and D-- those UHF ranges will eventually fill up with more wi-fi stuff.

I have seen even more detailed breakdown charts of frequencies but don't know where to get those. This was the right level of detail at this shopping phase

By the way, I saved $80.00 over retail for a factory-sealed new system.

And- unless it arrives in a million pieces of something -- that's... the rest of the story.

Gooooood day!

-Loren
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Old August 21st, 2006, 08:02 PM   #8
 
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Flip a quarter, it's just about as accurate.
Don't believe me? Check with folks that travel around the US as to the value of these charts, or talk to a Sennheiser dealer like Fred Ginsberg/Equipment Emporium.
Not saying the Senn's are bad units. Just saying the the charts aren't worth the paper they're not printed on as a general rule.
Buy the band that is least occupied in your area. That's the best short term answer. There isn't a long-term answer, because every area of the US is different if you're traveling, which your post seems to suggest.
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Old August 25th, 2006, 03:00 PM   #9
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Quote:
Originally Posted by Douglas Spotted Eagle
Flip a quarter, it's just about as accurate.
Than what? The general country-by-country charts? Thanks, I like the granularity here, even as a point of departure. As for accuracy, are you saying the layout of FCC-licensed UHF stations listed in each city is inaccurate? You should bring that to the attention of the folks at Sennheser. Meanwhile, I find it handy.

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Old August 25th, 2006, 03:07 PM   #10
 
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The usefullness of the chart isn't all that great in terms of selecting frequencies. Of course the licenced information is accurate, but that bears little relevance to selecting frequencies, any more than promising 200 channels, etc. Marketing hype and reality, regardless of the manufacturer, are usually two different things.
I'd just as soon not argue; if you find it useful, that's all that matters, yeah?
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Old September 1st, 2006, 01:09 PM   #11
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Douglas, there's no arguement here. You're a fine writer and I respect your work. When you offer a casual remark, especially in an INFO forum, it's best to provide a corrective. I have yet to find a better guide for city frequencies, if only to help me avoid major UHF channels. Is there anything better?

- Loren

Last edited by Rob Lohman; September 2nd, 2006 at 03:47 AM.
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Old September 2nd, 2006, 05:48 PM   #12
 
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Having a list of "open channels" doesn't mean much at all in the grand scheme of things. It doesn't take into account DTV, doesn't take into account other RF sources, and most of all, can't possibly take into account other forms of interference.
Most any professional sound engineer that travels with rock bands, Broadway shows, film crews, Disney on Ice shows, etc will explain this much more emotionally than I might. It's a waste of time, using the charts overall, but if you feel it benefits you, then all that matters is how you feel.
Having traveled with all of the above productions at one point or another, I'll tell you we use wireless management, and in the case of large productions, we interface with an RF/Wireless coordinator that ALL large events will hire or make available, and no one uses those charts. Complex frequency maintenance programs are used, being sure that frequencies are at least 150Khz apart at all possible times, making sure no one steps on anyone else' toes, and making sure that no one "sneaks" in a wireless frequency that they haven't had approved.
A chart merely shows what licensed locations are using; wireless systems and radio-control systems aren't licensed. In fact technically, they're a violation of FCC ordinances. Having a chart, along with advertising "We offer XXXX # of frequencies" is basically marketing hype, and as soon as you start traveling with 2 or more wireless rigs, this becomes immediately apparent.
The UHF bandwidth allocated to our industry is like a freeway of four lanes. You can divide those four lanes into as many frequencies as you want to for marketing purposes, but the bottom line is that you only have four lanes in real life. Cars/ radio transmissions don't become thinner to fit in the thinner lanes. And when that Mack truck of DTV or other local interference is in your lane(s), you can have all the charts in the world, it still doesn't help you get out of the lane fast enough. It just runs you over and leaves you in interference hell.
To summarize, pre-production, on-site testing are the only reliable means of locating usable frequencies. Hence the term "flip a quarter."
While you might feel this is my opinion Loren, you'll find it's the opinion of virtually every traveling production engineer that sets up wireless' on a regular basis in a variety of cities. FWIW, I didn't coin the "flip a quarter" analogy, that honor goes to a Tony, Emmy, and Oscar winning/nominated sound recordist/engineer that writes for Mix magazine. I'm just not that eloquent.
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Last edited by Douglas Spotted Eagle; September 2nd, 2006 at 07:43 PM. Reason: typo
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Old September 2nd, 2006, 07:31 PM   #13
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Quote:
Originally Posted by Douglas Spotted Eagle
being sure that frequencies are at least 150Mhz apart ...

In fact technically, they're a violation of FCC ordinances.
I think you mean kHz. You aren't going to accomodate many users at 150 MHz spacing.

Many wireless mics are approved for use by the FCC. If you find something like "FCC ID: DVMOB2EUVL" this means that the device is "Type Accepted" by the FCC (meets their specs and has been tested to their standards) for use under Part 15 of the regs. This means that the device can be used provided 1. That it causes no interference to licensed systems on the frequency used and 2. That the user agrees to accept interference on that frequency. If the unit does not have a type acceptance number then it is not legal to use it in the US.

The best way to pick a band for a particular venue is to do a spectrum survey at the location to be used. This involves using a device called, unsurprsingly enough, a spectrum analyzer though one can do a survey with a vanilla "short wave" receiver as well as long as it tunes the frequencies of potential interest. If you have a type accepted device you can choose a channel and then listen on that frequency with the receiver or look at that frequency with the SA. If the frequency is clear it's probably safe to use it but the fact that it's clear now doesn't mean it will be tomorrow. At this level and beyond the process gets pretty geeky/engineery quite fast. If there is a spectrum manager to consult, by all means use him.
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Old September 2nd, 2006, 07:43 PM   #14
 
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Quote:
Originally Posted by A. J. deLange
I think you mean kHz. You aren't going to accomodate many users at 150 MHz spacing.


The best way to pick a band for a particular venue is to do a spectrum survey at the location to be used. This involves using a device called, unsurprsingly enough, a spectrum analyzer though one can do a survey with a vanilla "short wave" receiver as well as long as it tunes the frequencies of potential interest. If you have a type accepted device you can choose a channel and then listen on that frequency with the receiver or look at that frequency with the SA. If the frequency is clear it's probably safe to use it but the fact that it's clear now doesn't mean it will be tomorrow. At this level and beyond the process gets pretty geeky/engineery quite fast. If there is a spectrum manager to consult, by all means use him.
LOL, caught me typing too fast, didn'tcha :-) Thanks for the catch.
Yep, you'll always find spectrum analyzers on high-profile jobs, and even on many smaller events using more than 6 systems or so as well. For "Unforgettable" in NYC, it took 6 hours of pre-production testing before we could figure out a frequency plot, and as you point out, it doesn't last forever. The Olympic frequency management was incredible; you should see the list of times/operating freqs, etc. like a phone book for a small city.
BTW, higher end wireless systems offer scanning as part of the system. So far, they've worked fairly reliably, but always be prepared for scary changes between morning soundcheck and evening events.

This subject is a fairly redundant subject, a quick search would reveal a number of posts on the subject.
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Old September 3rd, 2006, 11:16 AM   #15
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Quote:
Originally Posted by Douglas Spotted Eagle
It doesn't take into account DTV
Actually, it does. It merely shows the UHF channel assignments(including DTV) in a given area with an overlay of the A, B, and C frequency range offered. It's not meant to be the be-all end-all of accurate information for a given event. It's a guide for potential buyers to select the frequency range having the least number of assigned channels in their geographical area.

Of course it doesn't take into account every wireless UHF source out there. Common sense would dictate coordination of wireless sources at the types of events you listed using a good spectrum analyzer.

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