700 MHz LTE Interference with ATSC? - Canadian TV, Computing and Home Theatre Forums

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post #1 of 29 (permalink) Old 2014-05-13, 09:52 PM Thread Starter
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Question 700 MHz LTE Interference with ATSC?

I've been having issues for the past few months... I thought I had a bad antenna, but something seems to be causing interference on all channels. My signal reads half as strong as it use to and all channels stutter every few seconds. I'm getting this on 2 different receivers.

Now I'm reading that LTE, which is using 700 MHz, can be causing this type of interference. This is happening because 700 MHz was used for ATSC before it was auctioned off to the cell phone companies. My receivers, antenna, and amps will all pass 700 MHz.

Is anyone else having this same issue? I see Tinlee is selling a filter just for this purpose so it must be a problem.
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post #2 of 29 (permalink) Old 2014-05-13, 11:09 PM
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My understanding is 700MHz LTE in Canada was launched ~ Mid April in a few select urban areas.
Given the fact 700 MHz LTE hasn't been in use in Canada for "the last few months", I doubt that's your issue.

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post #3 of 29 (permalink) Old 2014-05-13, 11:34 PM
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And even if a 4G/LTE transmitter WAS within a couple miles of your location, InterMod Distortion Products would only fall on top of the UPPER channels....

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post #4 of 29 (permalink) Old 2014-05-14, 12:58 AM
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HDTV101 there has been quite a bit of tropo in the Toronto area lately, but you said the interference is on all channels, so I doubt it is that.
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post #5 of 29 (permalink) Old 2015-05-11, 11:52 PM
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I had similar problems(Orangeville Area). 2 weeks ago installed a new CM7777 preamp, lost all my channels except for one. Sometimes I would get stations, then they would be gone. Ones that I consistently receive like CBC(RF20). Tested all my cables, voltages etc. Called Channel Master support. They said may be cellular, fire or police transmitter overdriving the pre-amp. They did not have any solutions except to replace the pre-amp with a CM7778. I called Angel Electronics where I bought the pre-amp and they recommended installing an LTE filter($15) after the power inserter(TV side). This did not work. After a little research found that the filter must be placed between the antenna and the pre-amp. This solved my problem. Apparently the frequencies from channels 60-69 were assigned to the cellular range sometime during March/April, 2015.
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post #6 of 29 (permalink) Old 2015-05-12, 01:39 AM
 
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Nearby WIFI can really kill ATSC S/N... in fact just about any nearby signal (frequency or location wise) can interfere. Some of the newer consumer wireless router radios are unfiltered, so spurs show up way out of band. Gets worse with after-market firmware that allows users to crank up the power to get better range...which just causes the radios to splatter all over the spectrum. Many commercial operators are guilty of doing this as well.

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post #7 of 29 (permalink) Old 2015-05-12, 02:47 AM
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Reminds me an awful lot of GerryB's problems in Ottawa in 2011 described in the following thread:

Severe OTA Interference From New Digital Services Tower
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post #8 of 29 (permalink) Old 2015-05-12, 08:46 AM
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Nearby WIFI can really kill ATSC S/N...
That would indicate a poor quality or defective receiver. WiFi, at 2.4 GHz is more that 3x the frequency of the highest TV channel. Properly designed and build receivers should not respond to it. As for "LTE", that's on an adjacent band, so it can cause problems in TV receivers.

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post #9 of 29 (permalink) Old 2015-05-12, 12:20 PM
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It's just as likely to be a defective WiFi device. Considering the proliferation of wireless devices using former TV frequencies, it's probably a good idea to install a low pass filter such as the LTE filters mentioned earlier.

I have a similar issue with spurious interference here. It affects mostly VHF channels but does extend into the lower portion of the UHF band. I suspect the interference is being spread by local overhead power lines from a source either nearby or some distance away. Industrial and some commercial grade equipment is a common source of such wide band interference since it has far fewer restrictions on EMI emissions when compared to consumer products. Street lighting can also be a source of interference.

About 20 years ago I had issue with FM reception. I suspected that it was due to faulty two way radio equipment due to the pattern, which was during business hours only on a specific frequency and it was city wide. At that time, Industry Canada had the resources to investigate and track down these types of issues. These days, they won't.
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post #10 of 29 (permalink) Old 2015-05-12, 12:54 PM
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^^^^
If a WiFi device was creating interference on the TV channels, it's not operating within the regulations. Also, if that was the case, then a low pass filter on the TV wouldn't help, as it would pass the interference along with the desired signal.

Years ago, I also experience interference from a paging system. Turns out the problem transmitter was twice the IF frequency from the station I was listening to. This indicated a poor front end in my receiver.

All devices capable of producing interference to licensed radio services must meet IC specs. In fact, the ISM bands, used for WiFi, microwave ovens etc. were created as a place where those devices could create their noise, without interfering with the various services. It was only later that those bands were used for things like WiFi, wireless mikes etc.

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post #11 of 29 (permalink) Old 2015-05-12, 10:07 PM
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Originally Posted by ExDilbert View Post
It's just as likely to be a defective WiFi device. Considering the proliferation of wireless devices using former TV frequencies, it's probably a good idea to install a low pass filter such as the LTE filters mentioned earlier.
HDTV101 uses a tower placing his antenna well above rooftops. And I'm sure that he uses quality coax, most of which is swept to 3Ghz for interference resistance. I doubt WiFi would interfere in this scenario.

In terms of devices using former TV spectrum (other than cellular at 700MHz): Has this been implemented in Canada? I know the FCC approved white space spectrum for some devices, like wireless mics. Not sure that Canada has followed suit.

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post #12 of 29 (permalink) Old 2015-05-12, 10:14 PM
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Years ago, I also experience interference from a paging system.
Briefly off-topic but somewhat related:
When I worked for Rogers, we had a similar issue for our cable subs in a smaller southwest Ontario town. Turns out we had hired a new contractor to install analog channel filters, and they had only finger-tightened the f-connectors. A local paging transmitter's signal was ingressing into the loose connectors. Expensive fix...sending techs to check all of those filters.

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post #13 of 29 (permalink) Old 2015-05-12, 10:50 PM
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An OTA tower or even a rooftop install would certainly have the height to 'see' leaky Coax from nearby Cable TV lines in a given neighborhood. But not so high that it would be immune from Cable TV leaks in proximity...
Many cable TV transmission lines / connectors are extremely old, and a preamp in the OTA system will tend to 'pull it in' from further away...
even just a little is bad because it's gonna be co-channel to everything, not just in an adjacent band.
There are many possible sources....

I think Gerry's case was kind of unique in that there were antennas on a rooftop directly across the street, facing right at his window...

On a sidenote, When I first put up an antenna here (was it 2009?? ouch...), it was more or less just an experiment and I used whatever old coax I had lying around at the time.
The other day I put up a brand new run of "DirectTV swept to 3GHz coax", dressed it up nice, replaced a balun, just because. Also replaced a few jumpers,
just because... Just a couple data points in time, but made me feel better...
red line is like a year ago, green line was today...

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post #14 of 29 (permalink) Old 2015-05-12, 11:30 PM
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I agree that it's probably not a WiFi device but I wouldn't rule it out 100%. It sounds very similar to the issue I have here. It affects mostly VHF channels but I've also seen it on weak UHF signals. I've seen similar interference before and it's fairly common. The source is often electrical and can be caused by electrical arcs. One common source is electric motors turning on and off. They are in many appliances, including refrigerators, freezers, furnaces, washers and dryers. It's not usually the motor itself but arcing inside the thermostat or controller that is the source of the RF. Other sources I've seen are high voltage baseboard thermostats, PCs, florescent light fixtures or their lamps and street lights. I've seen wide band interference from all these sources and it can be very difficult to track down. They can travel some distance, sometimes several kilometers along hydro lines from high some high level sources such as industrial plants.

Anther possibility is a defective RF transmitter that is emitting wide band interference. That's less likely because they generally only emit interference on harmonics of the main signal but it's possible. Another possibility is that a nearby transmitter is causing an OTA preamp or other piece of equipment to overload. A filter will often correct that but removing the preamp is a good way to determine if that is the cause. Don't underestimate the ability of nearby, low power, low frequency transmitters used for fleet dispatch to cause TV equipment to overload. I've often seen that.

The problem cannot be corrected in the same way that it can with cable TV. While good cable integrity is important for OTA, the OTA antenna itself picks up the interference so it's often not a cabling issue. I'm not saying that electrical interference is the cause of the issue but it's one possibility. Like I said before, this type of sporadic interference is very difficult to track down. A start would be to eliminate possible sources from inside the residence. That can be done by turning off equipment to see if the interference is eliminated. Another possibility is to turn off all circuits and equipment except the TV tuner or TV. If the interference goes away, it's an internal source. If not, it's probably external. If it is internal, turn on circuits and equipment one at a time until the interference returns.
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post #15 of 29 (permalink) Old 2015-05-13, 12:00 AM
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DrawdotQuick solved his problem ~ yesterday, by installing a Low Pass Filter. HDTV101's post was over a year ago. I could be wrong but I don't think he is still looking for a solution to a problem

I was just offering an often overlooked but obvious source of potential issues... The only solution to Cable TV egress would be to get the cable TV company to fix it, of course assuming you had enough evidence and could convince them there was an issue on their end.

below pic is from about 30 ft away from a telephone pole showing signs of some egress, with just an RTL SDR dongle as a receiver and a yagi for an antenna,
no external pre-amplifier. It's not likely strong enough to trigger the Cable Co to go out and fix that, unless it was significantly stronger in the VHF Aircraft band.
But imagine that being in yours or your neighbor's backyard... Amplify that by say 20 dB with the typical OTA Preamp, and I am sure that could cause one some reception issues on weaker distant OTA signals.

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