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Old August 7th, 2010, 06:21 PM   #1
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700 mhZ ISSUE

In this month's issue of Broadcast Engineering there is an article on page 10 in the Feedback section that appears to be a late insert quote "The FCC has proposed new rules that would allow legal, unlicensed operation of TV-band wireless microphones by anyone at powers below 50mW. There are also proposals to expand eligibility for licensed microphones above 50mW beyond the present group of broadcast, cable and film producers."

Has anyone else heard anything about this? Does it mean that we may get back the usage for some of our wireless microphones in the 700mhZ range? I just hate to see those good microphones and receivers sitting on the shelf gathering dust. Also my new microphones and receivers do not seem as sensitive as the old ones and interference is really a major problem at large outdoor events.

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Ronnie Martin
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Old August 9th, 2010, 04:30 AM   #2
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the US TV band is now channels 2-52. don't count on getting the 700 band back, it's new owners have paid too much money to be there. operating in 700 illegally can carry huge penalties and i assume the interference of the new services would make it unusable anyway.

the remaining TV space is more crowded than ever. more channels in a smaller spectrum, and digital stations can exist on consecutive channels numbers, something that wasn't possible with analog, resulting in a lot less space for users like us. add to that the fact that our analog receivers don't always "see" a digital station when scanning for open channels, resulting in interference on channels suggested for use. i always try to research digital stations on antennaweb.org, or sennheiser's frequency finder page and then manually avoid those frequencies.
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Old August 9th, 2010, 10:43 AM   #3
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Thanks Greg: I was just hoping.... I have purchased new microphones and receivers which was a major purchase for a small bottom feeder like me. Also I check out the frequency allocations of the TV stations from the same document that you refered to before going to a new venue. When all my microphones were up in the 700 range, for years I never encountered interference. However, now that I have moved down I find much more interference from other transmitters. I shoot racing video at different tracks every weekend and produce a TV program that air locally on 4 TV stations across the state. All of the tracks depend on hand held transceivers to communicate with the track officials and interference is really a problem. Very few of the people operating these transceivers have a clue as to what frequency they are operating on. I usually look on the transceivers to see if the frequency is stamped on the back. Most of them do not have the operating frequency printed on back of the unit. Sometimes these transceivers are operating just close enough to my frequency that from time to time during the shoot my receiver is swamped and drops out.

Thanks again for your reply

Ronnie Martin
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Old August 9th, 2010, 02:06 PM   #4
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This is where frequency agile systems are a blessing. There is a lot of bad stuff out there, but that being said, there are still plenty of holes out there for wireless mics. I work in one of the worst wireless environments in the country- on top of a hill in downtown Los Angeles. Between the DTV stations, local film shoots, etc... you can never count on any frequency being free for a full day.

Our MO is to scan the frequencies of our wireless and figure out what is open that day. We move the packs and the receivers to those channels and we're set most of the time.

A couple hints if you are looking at the charts to find free space:

1. Look for the strengths of the transmission of various stations on the charts. You'll find that each one takes up 4 MHz of bandwith (or was it 6? brain isn't entirely working right now).

2. If you're scanning, you'll see a spike in level at the top and bottom frequencies of each station

3. There is a buffer between each station to prevent interference. Between high-power stations, that hole for the buffer may look like a great place, but it is going to be problematic most likely. Between the low power stations, the hole may not look as big, but you'll have better luck there.

4. There will likely be open spaces for stations that are not in your exact location. Here in LA, the orange county stations don't reach into downtown much, but the space is still open everywhere due to the way the licensing works. Means those can be great holes for putting mics

Not to fret about this stuff... you just need the flexibility to deal with it.

--Ben
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Old August 9th, 2010, 06:09 PM   #5
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My new system is from Sony and it is frequency agile. If it were not I would not be able to use it in my area. I can hardly imagine the problems you have in LA. I am a ham operator and on one of my trips to the left coast a few years back I took my UHF/VHF hand held with me and there was so much rf everywhere that I could hardly use it. Not only were the ham bands completely full but the commercial bands also.

Lately when it is possible I am back to using my wired system just to avoid the possibility of interference.

I guess what I liked about the 700 band was the complete lack if interference in my area. I never had to change frequencies.

Take care

Ronnie
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Old August 9th, 2010, 06:51 PM   #6
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what freqs are your sonys? i'd stay as close to the top of 600 band if possible. the walkie talkies are probably around 5W output, and probably 450-470 MHz. Key this up next to your receiver and your gonna get front end overload and loose your rf mic. the more your can stay away from their channels and radios the better. are your receivers the on-cam battery powered type? moving to a unit with external antennas, and putting a band pass filter inline might help. the band pass filter will only let a certain range of channels through to the receiver and help block out the radio guys. but its not a rig you can be mobile with. i keep saying it would be nice to have a "wireless mic" band that we can safely invest in. maybe this new effort by the FCC is a step that will help. new mics in a band above 1GHz might be a good solution too. tough times for wireless...
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Old August 9th, 2010, 07:30 PM   #7
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The frequency range of my transmitters and receivers is 566.125 to 589.875. I have lately just been looking the the Shure document on TV frequencies and picking one as far away from the TV stations as possible.
I shoot in several locations across the state that all have TV stations on different frequencies. The transmitter model number is UTX B2. The receiver is URX P2 30. The receiver is the on camera type. I know these are not the high end models and more than likely the front end of the receiver is not as good as the more expensive ones. However, it was all we could afford considering we had to junk all our other gear.

We do on track interviews before and after the races and it is hard to get down there with anything else but a wireless. We take the feed their board and feed it into the UTX B2 and then everything that is said over the pa system is transmitted to my camera. For the interviews before the race we use a hand held microphone that came with the kit. During the pre race interviews I have not had any interference. It is during the race when all the officials are using their radios that I get interference. Next time before the race I will key up one of the officials radios and see if it swamps my receiver.

The 700mhZ set up that I had seemed to have more range. I know that it is line of sight. However, I could walk around all over the track and be able to hear the transmitter on 700mhZ. It was set on the upper part of the band from the factory and we never had to move it. Actually at 700mhZ there is more penetration through walls and other obstructions than at the lower frequency. The lower frequencies should have slightly more range. When I first started shooting race footage about 10 years ago I had a VHF Azden set up that had only two frequencies and it had the best range of anything I had. Actually when everybody moved up to UHF the lower frequencies VHF were really not busy. I always take the old VHF setup with me as a back up. Maybe I should go back down there and try it again if I am having trouble.

Thanks again for all your help.... I will just have to be more diligent on my frequency selection.

Ronnie
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Old August 9th, 2010, 08:42 PM   #8
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I thought the 700 MHZ range was put aside for emergency bands only?My wireless system only uses 30Mw am I o.k. to use this leaglly?
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Old August 10th, 2010, 04:31 AM   #9
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Quote:
Originally Posted by Randy Johnson View Post
I thought the 700 MHZ range was put aside for emergency bands only?My wireless system only uses 30Mw am I o.k. to use this leaglly?
Not true. The 700mHz band is used by other users as well as public safety . As of this year, and at the present time, ALL unlicensed use, such as wireless mics, in the band is illegal in the States regardless of power output.
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Old August 10th, 2010, 09:28 AM   #10
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Also remember that when multiple transmitters are in use simultaneously, especially the high-powered walki-talkies nearby, they don't actually have to be on your frequency to cause significant problems.
The intermodulation between two transmitters on two different frequencies creates interference on many other frequencies, one of which may fall directly on your selected frequency. In essence these intermodulation by-products become "ghost" transmitters, multiplying the problem.

Shure and other manufacturers have computer programs that can display this and help pick frequencies to use, IF you know all the nearby frequencies in use, which I'm sure would be very difficult or impossible to find out completely.

You can also link an antenna and scanning software to this intermodulation calculating software, but that adds more expense and equipment to carry. Plus many of these walki-talkies will be used intermittently, making them difficult to scan successfully if multiple groups at the track are on different frequencies.

I don't envy your situation!
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Old August 10th, 2010, 10:27 AM   #11
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My reciever have a RF meter on them and I can tell if somethings using a carrirer near by and I have 120 channels to choose from until I find a clear one. But that wont help in the "push to talk" world I imagine because they can just pop up. I'm probably going to get a new system I just need to get through the year. I let wasting a $1,500 wireless kit.
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Old August 10th, 2010, 01:31 PM   #12
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Ronnie, out of curiosity is your transmitter set to high power? Look between the antenna and battery icons. You should see "H". If it's "L" switch it in the menu.
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Old November 1st, 2010, 05:59 PM   #13
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Thanks it is set on high power.

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Old November 2nd, 2010, 10:45 AM   #14
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When outdoors and at a distance, setting to High can be very beneficial.

When indoors and at short distances, setting to Low can actually be helpful. It will reduce the chance of getting multipath interference, where your own transmitter signal bounces off some object in the room or inside the walls and acts like a ghost transmitter on the same frequency (because after all, it IS on the same frequency!).
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