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Old 2011-02-16, 05:03 PM   #1
GerryB
 
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Exclamation Severe OTA Interference From New Digital Services Tower

Ive had the unfortunate experience of having a base station for some kind of digital cellular service placed within about 70 m of my home. They apparently have a frequency of 734 MHz and a bandwidth of 10 MHz, running 1200 watts ERP. In addition another 3000 watts ERP of PCS/cellular went up in the same place. I no longer have good reception of analog channel 60 or 43, which I normally have more than 50 dB of fade margin since it is line of sight (check my TV fool results for being at top floor of 169 Lees Ave : http://www.tvfool.com/?option=com_wr...7ebb9ea9ac5185 ) Also getting pixelation on some digital channels that used to be perfect reception. Further signals that were reliable, like WCFE, are completely gone and never seen, even though last winter were a common occurrence.

Very scary actually since the digital signals are so strong I can hear them on my wired telephone and my piano even, to the point where they are very distracting.

I wrote Industry Canada - the district office - a letter about my problems of interference. In the meantime no more TV - even local TV - for me. Very sad.

I just checked and the 734 MHz transmitter corresponds to channels 58 and 59 UHF
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Old 2011-02-16, 05:42 PM   #2
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I've never heard of a cellular tower with an ERP over 100 watts. In the US, the FCC will authorize up to 500 watts maximum. Though it's rare that anything actually works over 100 watts.

The 734MHz transmitter must be experimental. The good news is that it's easy to build a stub filter at home tuned to that frequency. Or, to purchase a notch filter.

After the digital transition, I would switch to a pre-amp (if you use one) that only amplifies to channel 51.
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Old 2011-02-16, 06:00 PM   #3
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Check the Industry Canada TAFL. plop in my coordinates 45.4154 north by 75.6720 west, and see for yourself. http://sd.ic.gc.ca/pls/engdoc_anon/w...raphical_input It is bad. DDMMSS is 452455 by 754017

I actually used to build pre-amps with low pass filters for channel 50 and below only - using a very nice 54143 preamp design I came up with. That has been completely shelved. The interference Im getting is WITHOUT a pre-amp. Here is the text of my complaint:

To whom it may concern,

I am writing to submit a formal complaint of interference to my television reception of Ottawa UHF TV channel 60 ( at 746 MHz CFMT-tv "Omni 1" network) as well as UHF TV channel 43 (at 644 MHz, CHRO-tv "A Channel" network in Ottawa). I have a line of sight to both of these stations with normally a perfect picture on both with loads of fade margin. I live at 169 Lees Avenue on the top floor (13th) facing south. Both of these channels show a very distracting pattern of interference now. I do not have a pre-amplifier attached to my antenna, which is a simple dipole plugged into a coax plugged into the back of the TV set. I actually have 2 TV sets both of which are having these interference problems. One of the TV sets is a recent LG model which also has an HD tuner. I have also noticed some pixelation on HD over-the-air channels that was not there in the past. I have tried moving the antenna many places but it has not helped.

The same high-pitched whining sound that is coming from the TV from interference (Tv also has strong visual distortion) can also be heard on my landline non-wireless telephone and my computer speakers, as well as my electronic keyboard (again very distracting and is worst by the window where I spend most of the time in the apartment). I believe these to be rectified radio signals that are so strong that they overpower my basic electronic devices. They are non-stop 24/7 high pitch sounds. I have tried common mode choke coils and even shielding with tinfoil but nothing seems to work.

I live across the street from 180 Lees Avenue, where I have noticed 2 PCS/cellular base station antennas recently installed and pointed at a tilt angle directly toward my apartment. They are about 68 meters away when looking at a map on Google Earth. I looked at the Industry Canada TAFL and there are apparently 2x 955 watt ERP base stations pointed at 290 degrees azimuth toward my apartment from 68 meters away with what appears to be a tilt angle directed at my apartment (license number 1382963), a single 800 MHz base station of 600 watts ERP pointed directly at my apartment, and a 1200 watt ERP base station transmitting at 734 MHz (license number 5110000).

There are other base stations on the building across the street but they are pointed elsewhere. I have calculated the total ERP of these combined 4 stations at 3710 watts ERP, or times 2.2 = 8162 watts EIRP (effective Isotropic radiated power). I must admit it is unnerving to live in a place that is fully exposed to these emissions. The filed strength at 75 meters (add from 68 horizontal meters displacement) would be 100 mW/meter square, which is only about 17 dB less than safety code 6 (and closer if you count for internal reflections in my apartment).

Is there anything you can do to help me with this severe radio interference?

Thanks,
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Old 2011-02-16, 06:32 PM   #4
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I'm not doubting you. In Ottawa there is always odd stuff going on with RF testing. And it looks like Rogers got their 700MHz test license for LTE, as I suspected. Odd that it's throwing out so much power....

Either way, I'm guessing this has to be temporary. There's no way a production real-world LTE (or other cellular network) will need to put out that kind of ERP.
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Old 2011-02-16, 06:47 PM   #5
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Yep, I caught my error in calculations right away.

The problem is likely exacerbated by the fact that most digital TV tuners aren't designed to reject that kind of power on adjacent channels---your tuner is no doubt being completely overwhelmed.

I would try the stub or notch filter solution. Or a low-pass with >40dB of attenuation.
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Old 2011-02-16, 06:48 PM   #6
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All the transmitters on that roof are running about 1000 watts erp each. I cant believe they would do something like that in a residential area. It's absurd. The PCS and cellular must be permanent at 1000 watts each, so why would the LTE not also be permanent at 1200 watts ERP? The craziest thing of all is the tilt angles. Normally you point the beam horizontally and not down at someone's apartment.

To put it in perspective, it is like living next to 8 microwave ovens that have the door open and set at maximum cook.
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Old 2011-02-16, 06:56 PM   #7
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>>The problem is likely exacerbated by the fact that most digital TV tuners aren't designed to reject that kind of power on adjacent channels---your tuner is no doubt being completely overwhelmed.

I think that is the case with 43 but with 60 it is just out-of-channel emissions off their LTE transmitter.
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Old 2011-02-16, 07:07 PM   #8
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Well, your tuner can likely go up to channel 69. Either way, even strong out-of-band interference can mess up a tuner.

Most cellular antennae in urban areas are at least 10 degrees down from horizontal. So this makes sense. It's the incredible ERP that doesn't make sense. Think about it: Most hand held devices put out 4 watts maximum. What's the benefit with having such a disparity between the tower and device?!

I agree that such high power networks should not be deployed in residential areas. No doubt your neighbours are experiencing interference as well. Have you thought about posting a notice to get people complaining about it?
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Old 2011-02-16, 07:07 PM   #9
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Could you possibly post a picture of what this interference looks like with your most affected analog TV channel? I am interested in what this looks like.
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Old 2011-02-16, 07:18 PM   #10
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This is as good as I could get the picture on channel 60. It is totally noise when the antenna is at many angles



I used to get this channel with a paperclip with perfect reception. Now it looks like someone is operating a blender next to the TV set to a weak channel (channel 60 is over a megawatt in Ottawa)
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Old 2011-02-16, 08:11 PM   #11
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Ouch. That's very bad. No way you'll be able to recover from that. Digital signals don't stand a chance.
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Old 2011-02-16, 08:28 PM   #12
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Jase-

Im going to see if the district office of Industry Canada will do anything about it over the next week. If they don't do anything then I'll go to the Minister directly. It is totally irresponsible of Rogers to site those kinds of transmitters without at least getting them up out of the way of people. They could correct this with putting up an 80 foot mast on top of that building so the main beam is well over our heads, instead of just putting them at roof level. I'll get a petition going in the building if I need to.

There is a reason they want to transmit at high power though - actually a few reasons - 1st they are transmitting to multiple subscribers at once. 2nd there is an asymmetrical data flow in favor of downloading from the internet more than uploading. 3rd is that they have a controlled noise environment at the base station whereas on the ground a user may be in a localized very high noise floor environment, which means the base station needs to push out much more signal to get over the local user's noise floor, compared to what the user must push to get an equal S/N ratio at the base station receiver.
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Old 2011-02-16, 09:17 PM   #13
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I don't see noise as being an issue at 700MHz or higher though. I understand that some ERP disparity between tower and remote device is necessary, but that's a huge margin.

LTE is based on Code Division Mutliple Access---a wideband noise-based air interface. CDMA has been used by Bell and others for years, with no need for such high ERP base stations. CDMA, by it's nature, tends to require less transmit power to achieve similar results to narrowband technologies like 2G GSM.

I suspect the reason for the high-ERP is related to the test nature of the station. In real world use, 700MHz spectrum propagates very well...necessitating less transmit power. Certainly far less than 1.9GHz or 800MHz.
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Old 2011-02-16, 09:32 PM   #14
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>>In real world use, 700MHz spectrum propagates very well

That's one of my biggest problems. When the PCS 1.8/1.9 GHz went up first I found that I was able to put some tinfoil on the walls and get the signal down enough so I could use the telephone in some places. But with this 700 MHz stuff the tinfoil does nothing. It just follows me everywhere with a piercing ringing sound on the telephone.
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Old 2011-02-17, 02:45 PM   #15
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I'd be hopping mad if that happened near my house! Here's hoping IC gets on this asap and that a solution is quickly found.
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