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Severe OTA Interference From New Digital Services Tower

59K views 148 replies 27 participants last post by  qfurness 
#1 ·
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_wrapper&Itemid=29&q=id=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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#117 ·
No they are actually 2 unrelated events. I ordered the filter a few weeks back - and it finally came. I think the person from Rogers is with wireless - but you gave me a good idea - they probably have good filters that cut off at 680 MHz instead of 600 MHz. I will ask.
 
#120 ·
They definitely came and saw. I knew they were not used to it when one of them said "it's off the charts". They had a preamp on their spectrum analyser so they had to shut it off. It was one of those integrated spectrum analysers with a log-periodic antenna - the expensive kind.

They were super-courteous and knowledgeable, which was nice. Normally they look for interference into Rogers systems as opposed to the other way around.

When they shut down their systems temporarily, as expected, all the interference went away. I kept pointing out my main beef with the whole thing was the 700 MHz transmitter, which apparently is still just a set of carriers, which really worried me if they fire it up for real what it will do to the TV, being within the passband.
 
#123 ·
I understand Gerry is under no obligation. But if I were Rogers I would see a potential RF issue with future roll-outs. They have an interest in seeing that happens without a lot of nimby lobbying. No offence Gerry. I am on your side. But if they can pressure politicians to stop bulldozers or wifi they can stop an antenna from going up.
 
#124 ·
I dont want this running away with the NIMBY crowd, because a lot of what they say is junk science. Most of the towers you see going up have a lot of vertical clearance and reasonable tilt angles. The situation here is different. No walls to block or attenuate the signals. Residential area. Lots of KW of ERP. Less than 70 meters away.
 
#125 ·
With the kind of power their using why would they point antenna down when the signal from these cell panels could reach atleast 20km range.Ask them to try adjusting the tilt to straight out or no tilt.
 
#126 ·
Down tilt from horizontal is necessary for urban cellular installations to reduce interference with other cell sites using the same spectrum.
 
#129 ·
Here's applicable LTE output power "limits" paragraphs from FCC Rules Sec 27.50:
http://edocket.access.gpo.gov/cfr_2004/octqtr/pdf/47cfr27.50.pdf

a) Fixed and base stations: 1000 watts (60 dBm) EIRP, reducing to 65 watts
for 4500-ft HAAT (Height of Above Average Terrain)

b) Control stations and mobile stations: 30 watts (44.8 dBm) EIRP

c) Fixed stations: 30 watts (44.8 dBm) EIRP

d) Portable stations (hand-held devices): 3 watts (34.8 dBm) EIRP

e) Fixed and base stations: 50,000 Watts (77 dBm) EIRP, subject to sec 27.55 constraints:
http://edocket.access.gpo.gov/cfr_2004/octqtr/pdf/47cfr27.55.pdf

Remainder of FCC Sec 27 Rules can be found here:
http://www.access.gpo.gov/nara/cfr/waisidx_04/47cfr27_04.html

=======================================================
LTE in the 700+ MHz Band just fired up last year in a few major cities and it was
announced that more (incl. San Diego) were being fired up this year, although
where and when wasn't disclosed. So it will probably take most of this year before
a large number of users have 4G LTE devices and are actually using the new system:
http://latimesblogs.latimes.com/technology/2012/01/att-4g-lte-los-angeles.html

I'm still looking for interference analyzes and actual test reports, other than the
WSD adjacent-channel tests conducted by the FCC OET, CRC and others:
http://transition.fcc.gov/oet/info/documents [See DTV and WSD Test REPORTS]
Note that WSD EMI test found leakage into a NEWLY installed CATV system.
http://mstv.org/docs/1.31.07final.pdf [Three CRC Reports attached to the FCC Filing]
Note that WSD analyzes still apply for LTE interference to DTV, except the Next-next-next-etc
Adjacent Channel EMI is now of primary concern (e.g. N+1, N+2...N+7...N+14, N+15, etc).

Note that in the Super-Heterodyne STB/DTVs tested by the FCC-OET (see links above),
inadequate Image Rejection resulted in most (2005-2006) units under test being MUCH
more susceptible to EMI when it was 7 or 14-15 HIGHER than the desired channel. This
is easier to see on pg71 (of 145) in the CRC Report attached to MSTV's FCC Filing
(see link above). It is important to recognize that this means that a UHF DTV channel
will be MUCH MORE susceptible to EMI when it is about 42 MHz and 87 MHz higher than
the desired UHF channel frequency----smack in the middle of the LTE TRANSMIT BAND.
http://www.radio-electronics.com/in...iver-selectivity/image-rejection-response.php [Image Rejection Explanation]

So far, Charles Rhodes articles have concentrated on interference from DTV to LTE Devices,
not just adjacent channel (solved by on-going effort to vacate Ch51) but also third-order
Intermod products falling into the LTE User Device's RF input that may or may not be
filtered enough to prevent problems operating LTE devices anywhere "near" a DTV Tower:
http://www.tvtechnology.com/article/cell-phone-dtv-interference-issues-examined/210567
http://www.tvtechnology.com/article/solving-dtv-wireless-broadband-interference-problems/210841

Impact of LTE to CATV, esp Cable Modems:
http://www.cedmagazine.com/articles/2011/06/capital-currents-the-lte-interference-issue

====================================================
In Europe, LTE has been active in their 800+ MHz Band for quite a while, so in
the fol. reports, shift all frequencies down by about 100 MHz to see what would
happen wrt North America's 700+ MHz Band.
U.K.'s OFCOM sponsored an LTE interference to DTT test, measuring "typical" levels
that would cause interference to OTA, CATV and even SAT (coax carries TV freqs):
http://stakeholders.ofcom.org.uk/binaries/consultations/800mhz/statement/2010-0026.pdf
http://stakeholders.ofcom.org.uk/bi...area/projects/ddr/2010-0792_LTE_into_CATV.pdf

In addition to finding that Super-Het. type DVB-T tuners are ALSO more susceptible
when the EMI is 7 Euro-Channels higher than the desired DTV channel, the first UK report
also tested so-called "Silicon" tuners [i.e. Double Conversion, such as from Microtune],
finding that although they did NOT have the Image Rejection susceptibility (as expected),
the susceptibility on other frequencies was about 10-20 dB WORSE than Super-Het. tuners
[no doubt due to the lack of an input tuned filter]. Unfortunately, they did not recognize
the importance of this HUGE difference, which widens the susceptibility bandwidth.

Yup, TV viewers sitting around their living room and also using their 4G LTE devices
could disrupt TV viewing if they were really close (and with one DTV, further away).
This was "cured" by adding an "LTE Band Pass Filter" which provided more or less
20 dB of Loss on the subject test frequencies. Signals leaking into the cable system
via a leaky cable was also found in one particular TV device, cured with a new cable.

With the EIRP level noted above, nearby Cell Phone Towers are going to be a problem.
AND, I have yet to see an analysis for dozens to 100's of bar patrons interfering
with the big screen DTV hung on the walls.....Nor effect of 100's to 1000's of other
4G LTE signals coming into a roof-top antenna from the extended neighborhood,
esp. in crowded metropolitan situation (1000 mobile phones is a 30 dB increase in EMI).

Studies for the Netherlands:
http://ec.europa.eu/information_soc...docs/rsc30_item5_interference_studyreport.pdf
http://www.agentschaptelecom.nl/bin...lysis-of-interference-to-cable-television.pdf
And one for Germany & Austria (with imperfect translations):
http://rspg.groups.eu.int/_document..._digitaldividend_090515_0630/anga_annex_a.pdf

Here is a LTE-DTT Interference Overview from Rohde+Schwarz:
http://www2.rohde-schwarz.com/file_14100/1MA176_3e.pdf

Latest update re Telco responsibiity to FIX THESE PROBLEMS in Europe:
http://www.theregister.co.uk/2012/02/23/tv_4g_lte/

I'm surprised the FCC, et. al. have kept this dirty little secret for such a long time.....
 
#130 ·
FYI: I posted an assessment of candidate "LTE Low Pass Filters", finding Pico Digital's
LPF-700 to be the least effective, easily surpassed by Tin-Lee's LP7-700:
http://www.digitalhome.ca/forum/showthread.php?p=1388395

But due to slow frequency roll-off, it isn't optimized for use as an "LTE Low Pass Filter"
for AT&T's lower part of the 700 MHz Band, for uplink: 704 - 716 MHz, but would
suppress AT&T's data to users downlink: 734 - 746 MHz (Band 17):
http://en.wikipedia.org/wiki/E-UTRA#Frequency_bands_and_channel_bandwidths

Note that Verizon's 4G LTE frequency assignments are higher, with data to users,
downlink: 746 - 757 MHz and uplink: 776 - 787 MHz (Band 13):
http://www.pcmag.com/article2/0,2817,2388526,00.asp

Lower Block D (old Ch55): 716 - 722 MHz was until recently occupied by Qualcomm's
MediaFlo one-way transmitters, which were operating at 50 kW EIRP in our area.
FCC recently approved the sale to AT&T, but plans have not yet been fully revealed for
this UNPAIRED allocation (hence more suited for one-way broadcasts), other than for
additional capacity to users. LTE-Advanced (2014?) supports an auxiliary transmitter:
http://www.bloomberg.com/news/2011-...-airwaves-sale-to-at-t-wins-u-s-approval.html

Lower Block E (old Ch56): 722-728 MHz appears to be sparsely populated (update needed).
Qualcomm bought a small number of UNPAIRED licenses in major metro areas and Frontier
bought a few locations: http://www.phonescoop.com/articles/article.php?a=187&p=233

LTE (Band 14) can occupy even higher frequencies: downlink: 758 - 768 MHz and
uplink: 788 - 798 MHz.

So an LTE LPF could be effective against some LTE Cell Tower transmissions, but
would be hit or miss against AT&T's uplink transmissions from user devices co-located
with your DTV....and the 1000's if not 10,000's of OTHER LTE device signals being
received by a roof-top antenna....so YMMV....a lot....

I would expect that LTE LPF's specifically designed for North America's 700 MHz Band
should be coming to market in the near future....

SO....does this mean that I might have a problem since I'm in "AT&T Territory" (with a
major Cell Tower mountain only a couple miles away) and my son MIGHT have an easier
to solve (or NO) problem since he's in "Verizon Territory"????? [At least until they cross-mingle....]

While I'm not all that concerned with 1000 Watt EIRP (and under) Base Stations if they
are on nearby mountain tops, I would be very concerned if they were located on top of
convenient apartment and other hi-rise buildings. And those 50-kW monsters should
be confined to existing transmitter farms....still looking for a GOOD Cell Tower Locator
website that includes LTE operating frequencies....
 
#131 ·
LTE Details for the Ubber-Geek:
Also known as Evolved UTRA (E-UTRA) and E-UTRAN.

http://www2.rohde-schwarz.com/file_10948/1MA111_2E.pdf [UMTS LTE Intro]
http://www2.rohde-schwarz.com/file_13924/1MA169_2E.pdf [LTE-Advanced Upgrade]

http://en.wikipedia.org/wiki/3GPP_Long_Term_Evolution
http://en.wikipedia.org/wiki/E-UTRA#Frequency_bands_and_channel_bandwidths
http://en.wikipedia.org/wiki/LTE_Advanced

LTE Specifications:
http://www.3gpp.org/article/lte
http://www.3gpp.org/ftp/Specs/html-info/36-series.htm
http://lteportal.com/

Note that the LTE 3GPP Base Equipment Spec: TS-36.104 V10.5.0 (36104-a50.doc)
specifies +24 dBm max for one Base Station transmitter port and +20m dB max for
one Home Station transmitter port, both with +/- 2 dB tolerance for "normal" conditions
and +/- 2.5 dB tolerance under "extreme" conditions. When two or four transmit
ports are active at the same time (e.g. for Dual and Quad Transmit Diversity), the
output power is derated by -3 dB and -6 dB respectively to maintain the same average.
Antenna arrays (like DTV Transmitters) are use to provide Antenna Gain to reach the
desired EIRP.

LTE 3Gpp TS-36.101 V10.5.0 User Equipment Spec stipulates +23 dBm (+/- 2 dB)
Transmit Power with a 0 dBi Antenna Gain for Mobile User Devices, hence +23 dBm EIRP.

=====================================================
For convenience, I posted charts from FCC-OET 2005/2006 STB/DTV EMI Susceptibility
Test Report and U.K. OFCOM Cobham LTE Interference into DTT Test Results here:
http://imageevent.com/holl_ands/files/emitodtv
 
#132 ·
Verizon's 4G LTE (750+ MHz) Coverage Query by Address:
http://network4g.verizonwireless.com/#/coverage
Nearly ALL of L.A., Riverside, Orange and San Diego Counties are covered.
Very detailed coverage with lots of small dead spots, so appears to be accurate,
derived from an actual propagation prediction program.
Zoom out to see Regional and National Coverage....mostly around large cities.

PS: Apparently NO COVERAGE for Camp Pendleton and busy I5 that runs through it.
Or maybe the prediction program overlooked it because of no street addresses.....
That's going to make it more difficult for families headed to Disneyland to keep
their kids entertained or business executives make updates to their presentations
while they zip through at 80+ mph....

AT&T's 4G LTE (700+ MHz) Coverage Query by Address:
http://www.wireless.att.com/coverageviewer/#?type=data
Nearly ALL of L.A., Riverside, Orange, and San Diego Counties are allegedly covered,
although AT&T said that they only started San Diego service last month and won't be
FINISHED for "several more months".
But it doesn't show the many dead spots that users report, so it might be an
"artist's broad-brush mis-conception"....like other AT&T "coverage" maps....
Zoom out to see Regional and National Coverage....mostly around large cities, or use:
http://www.att.com/network

======================================================
Canadian LTE Overview (from Rogers Comm. Inc.):
http://www.ic.gc.ca/eic/site/smt-gs...on.pdf/$FILE/smse-018-10-lemay-submission.pdf

In Canada, the lower 700 MHz Band has not (yet) been auctioned off, although
there are trials underway in Ottawa.....networks MAY fire up late this year...prob 2013:
http://www.bill-mcminn.com/commentary/ltebasics.html
Note LTE will also be in AWS Band(s), which are much, much higher freqs...
 
#133 ·
The LTE at 700 is gone for now, but I guess I shouldn't be surprised to find out that theyve put up a few more transmitters in the 2100 MHz band pointed straight into my window, according to the Spectrum Direct service provided by Industry Canada. I added up the power and converted it to EIRP -- works out to about 15,000 watts in my direction alone. I have that nice buffer of 70 meters from the antenna though. Once they hit that magic 50,000 watts I'll have to get serious again - thanks for that Holl ands.

I forgot entirely about the letter they sent me back in May of last year. It goes something like this:


May 3, 2011
To Whom it may concern:

RCI conducted a visit to the Citadel Apartments located at 169 Lees Avenue, Ottawa on March 22, 2011. The purpose of the visit was to respond to a request concerning possible interference from Rogers' radio-frequency communication equipment into home electronics belonging to a tenant of the building, Mr Gerry B.

Observations confirmed that an electronic keyboard was producing audio noise while RCI's 700 MHz and 850 MHz radio transmitters were in operation. No degradation to the keyboard was observed while the radio transmitters were out of service. Degradation to the picture of a television receiver was also observed while Rogers' 700 MHz transmitter was in operation. A spectrum scan from 500 MHz to 3600 MHz confirmed that no significant contributions from other external sources were observed. It should be noted that the 700 MHz transmitter is currently operating under an experimental license granted by Industry Canada, which will expire on June 15, 2011.

Spectrum analyzer observations were performed using a Rhode & Schwarz FSH4 spectrum analyzer and a Rhode & Schwarz HE300 directional antenna. Rogers 700 MHz LTE carrier, 2100 MHz LTE carrier, 850 MHz UMTS carrier and 1900 MHz UMTS carrier were all visible. All carriers were clearly observed to drop when the transmitters were taken out of service. The observations confirmed that the Rogers carriers were present in their proper locations and that no spurious noise or other intrusions from the Rogers transmitters were seen at signal levels as low as -100 dBm, with the test equipment used.

Rogers confirms that no evidence was seen to suggest that Rogers transmitters were creating out of band emissions that would create interference into home electronic devices. Rogers also confirms there is an interaction between the Rogers transmitters and the affected electronics. The physical proximity of the Rogers antennas, the output power from the transmitters, the close proximity in frequency of the television receiver frequencies, are likely resulting in the desensitization of the television receiver, which does not have sufficient filtering capability to remove teh out of band signal. Since Rogers' equipment is not transmitting out of band and is operating according to Industry Canada license requirements, the resolution would therefore reside with Mr. B, the operator of the home electronics.

With regards to the degradation of the television, Rogers confirms that the experimental 700 MHz license under use will cease prior to June 15th, 2011, after which time Mr. B should not experience noticeable degradation as a result of Rogers' equipment. The electronic keyboard appears to be affected by both the 700 MHz carrier and the 850 MHz carrier. As noted, the interference from the 700 MHz system will cease on June 15th. Possible solutions to the interference from the 850 MHz carrier were considered in order to assist with the resolution of the issue, including the relocation of the antenna. This was determined to not be possible without impacting customer service since the coverage of the cell would be impaired.

Going forward, Rogers is agreeable to working with Mr. B to provide technical assistance and advice for helping him resolve his issues.

Sincerely,

----
 
#134 ·
Interesting letter Gerry. So they are basically admitting that they are causing problems, but they are within regulated limits so they aren't legally responsible, but out of good will are willing to help.

If they start transmitting again, I suspect they would be willing to buy a custom filter for you. Not sure if there is much they can do about your keyboard though (maybe buy you a new one that won't be affected, if one can be found).
 
#135 ·
4G/LTE INTERFERENCE TO DTV UPDATE:

Last year, 717-728 MHz was allocated as a DOWNLINK (Tower Broadcast) Supplemental Data Link (SDL), which should be available "soon" [likely already in selected "test" areas]. It will increase data rates in new HSDPA capable devices. SDL will become the PRIMARY interference source from 4G/LTE towers....and will be difficult to attenuate with a simple Low Pass Filter:
http://www.4gamericas.org/documents/4G Americas-Benefits of Digital Dividend-September_2012.pdf
http://www.qualcomm.com/media/documents/benefits-hspa-supplemental-downlink

4G/LTE in 716 - 728 MHz presumably in upcoming Release 11 (see Slide 50):
http://www.home.agilent.com/upload/...vanced_V2.pdf?cmpid=1-4254376024&cc=US&lc=eng
 
#136 ·
Specs for 4G/LTE Filter from Radio shack website:
http://www.radioshack.com/product/index.jsp?productId=12934420&filterName=Category

Insertion loss 1dB between 50-600MHz
Insertion loss 3.5dB between 601-698MHz
Return loss 12dB between 5-698MHz
Rejection 50dB between 740-1000MHz

NOTE: NO SPECS FOR FILTER ROLL-OFF CHARACTERISTICS IN THE CRITICAL 698-740 MHz REGION!!!!!

Note the 3.5 dB Insertion Loss for Ch36-51, which can seriously degrade sensitivity on HALF the UHF Band.
Unless you KNOW there is a 4G/LTE Tower within a few miles of your location, you probably DON'T need it.

I addressed effectiveness of various Low Pass Filters against LTE's 700 MHz Band here:
http://www.digitalhome.ca/forum/showthread.php?p=1388395
Radio Shack may be the least expensive, but it isn't very effective if an ATT 4G/LTE is close and you need a TRULY effective filter. Verizon 4G/LTE is in a higher band and hence is not as much of a problem. Fol. includes info on how to determine if you are close to a 4G/LTE Tower (there may be other, better methods):
http://www.digitalhome.ca/forum/showthread.php?p=1693522.
 
#137 · (Edited)
If you don't need to receive channels 49-51, a Soontai LPF-680 might be a good option. They haven't published specs for this particular model, but they do have specs for the LPF480. Assuming the specs can be correlated (and yes I know you should never assume), I would expect it to have more than 20dB attenuation above 700MHz and close to 50dB above 716MHz. As for the pass band, I would guess it will have less than 0.5dB loss under 600MHz, less 1dB loss up to 650MHz and less than 3dB loss up to 680MHz (educated guesses). One would have to see the actual specs for the LPF-680 to be sure however.

The big question is where can we buy this filter and how much will it cost?
 
#140 ·
I was curious, so I asked how much it would cost for a small order (10-20 units). They said:

such small q’ty samples have to be HAND MADE by our engineers so you must understand the engineering sample cost would be much higher than normal mass production parts. If you’d order at least 100pcs which is our MOQ for mass production line I can provide better offer to you.
and the unit price in the quote was US$299.00. :O

Out of curiosity, I asked how much it would cost for 100, and the unit price plummeted to US$5. Yes, you can order 100 for less than the cost of 2. Welcome to low cost region manufacturing. Both of these prices are FOB from Taiwan and there is a 5% handling fee for credit cards.
 
#138 ·
Rogers rolls out 700MHz in some areas

According to this thread, Rogers has begun rolling out 700MHz coverage in select areas. It would be interesting to see if anyone has noticed recent interference as a result?
 
#141 ·
Channel Vision 3102-104 Specs indicate it PASSES up THRU CATV Ch102 (660-666 MHz) and has a 4-channel wide Slope to the High Attenuation Region, which would start at about 666+24 = 690 MHz, which means it should be just what is needed for suppressing 4G LTE Cell Tower signals, unfortunately they don't indicate HOW MUCH ATTENUATION is provided (BOO, HISS)....but even 15-20 dB should be more than adequate:
Low Pass Filter Blocks Channels Above 105 ? 3102-105 | Channel Vision Technology
Low Pass Filter Blocks Channels Above 105
 
#142 ·
I have the Radio Shack 1500396 LTE low Pass Filter that Adtech characterised a while ago.
Left my Phone up top on the chimney doing some data sessions one day,
and ran 905Shmick's hdhomerun script to measure signal strength and quality on all received stations without it.
Then I put the filter inline between antenna and preamp, and did the same thing. I saw no noticeable difference in SNR at the time.
Thus I removed it from the system as it didn't seem necessary for me.

maybe I'll try that exercise again someday and post results here (we have an RF 49 here).
 
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