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post #18001 of 18323 Old 01-21-2020, 12:12 PM
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I'm about 24 miles west of Needham MA where most of the Boston stations broadcast from. But there's a hill about a mile from here and trees etc. I've never tried OTA reception from my location. I probably won't be trying to set up an antenna here for some time yet. I have helped a few friends set up for OTA reception in various locations locally. There always seems to be a problem with pixelation, which IMO, is the biggest problem that discourages more people from OTA reception.

To me ATSC 3.0 is attractive because the signal is supposed to be more immune to multi-path interference and also the ability to stream it throughout the building using the right tuner box.

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post #18002 of 18323 Old 01-21-2020, 02:56 PM
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Quote:
Originally Posted by rabbit73 View Post
The current designs would need to be modified to give more gain at the low end of UHF. The gain curve of a UHF antenna is not constant at all frequencies; it rises as the frequency increases. The max gain of the current designs is above channel 36. If you make the antenna a little larger, this will move the peak of the gain curve down in frequency.

If the gain curves for these UHF antennas are referenced at each frequency along the curve to a dipole or an isotropic source, then the curves are misleading. A channel 14 dipole will generate 3.3 dB more signal than a channel 51 dipole in the same RF field because of the dipole factor. I don't know how the models handle the dipole factor. The dipole factor is much of the reason that the high VHF transmitters are so much lower power than UHF transmitters.
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post #18003 of 18323 Old 01-21-2020, 03:06 PM
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Originally Posted by Steve347 View Post
I guess that this brings up another question... What kind of performance increase could be expected if the design was optimized for 14-36 vs. 14-51?
If the overall antenna size is kept the same then optimizing will only produce a small gain increase. In order to get a significant gain increase the antenna will have to be much larger.
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post #18004 of 18323 Old 01-21-2020, 03:43 PM
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Originally Posted by Calaveras View Post
If the gain curves for these UHF antennas are referenced at each frequency along the curve to a dipole or an isotropic source, then the curves are misleading.
Computer models give results in dBi, to compare the predicted performance of different designs.

Quote:
A channel 14 dipole will generate 3.3 dB more signal than a channel 51 dipole in the same RF field because of the dipole factor.
Yes, but an antenna designed for the UHF band is usually modeled at a frequency at the center of the band. This will make the antenna less efficient at channel 14 which is away from the design frequency, causing the gain curve to fall at the low end. The gain curve will rise above the design frequency because the elements are longer than a halfwave.

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I don't know how the models handle the dipole factor. The dipole factor is much of the reason that the high VHF transmitters are so much lower power than UHF transmitters.
I'm not sure how the computer models deal with the antenna factor. I don't do modeling and prefer to make performance measurements of antennas.

My guess is that the antenna factor only needs to be considered when using the field strength in dBuV/m just before the signal touches the antenna (as in converting dBuV/m to dBm). The model includes the antenna factor because the antenna size is scaled to frequency and includes the feedpoint where signal power is measured.

dBuV/m to dBm calculator
http://www.g4axx.com/
click on Downloads
click on dBuV to dBm calculator (xlsx 20kB)





Trip in VA uses a conversion factor of 130 for dBuV/m to dBm for his rabbitears.info Signal Search Map reports for UHF signals. For VHF signals, he adds a negative correction factor (to field strength; signal margin remains unchanged IIRC) to allow for the higher noise levels on VHF-High and VHF-Low. This makes them listed a little lower in the report.

This document shows that the FCC Planning Factors include the Antenna Factors for UHF, VHF-High, and VHF-Low. It also allows a higher noise figure for a VHF tuner, but it does not allow for the higher ambient noise level on VHF, which is why Trip added a correction factor to his signal reports that use the FCC TVStudy software.

Federal Communications Commission FCC 05-199
Report To Congress
The Satellite Home Viewer Extension And Reauthorization Act Of 2004
Study Of Digital Television Field Strength Standards And Testing Procedures
https://transition.fcc.gov/oet/info/...FCC-05-199.pdf
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post #18005 of 18323 Old 01-21-2020, 03:53 PM
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Quote:
Originally Posted by Calaveras View Post
If the overall antenna size is kept the same then optimizing will only produce a small gain increase. In order to get a significant gain increase the antenna will have to be much larger.
Yes, when an antenna design is scaled to a new frequency, ALL dimensions are multiplied by the same scaling factor, so the overall size will change.
https://www.digitalhome.ca/forum/3098227-post10.html

https://www.digitalhome.ca/forum/3098283-post12.html

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post #18006 of 18323 Old 01-23-2020, 02:23 PM
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The forums new format is gonna be a BIG change.

https://www.avsforum.com/forum/43-fo...l#post59143586
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post #18007 of 18323 Old 01-24-2020, 06:48 AM
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Quote:
Originally Posted by rabbit73 View Post
Yes, when an antenna design is scaled to a new frequency, ALL dimensions are multiplied by the same scaling factor, so the overall size will change.
https://www.digitalhome.ca/forum/3098227-post10.html

https://www.digitalhome.ca/forum/3098283-post12.html

Obviously that's true but that's not what I meant. There is a tradeoff for gain and frequency coverage for a given sized antenna. You can get a little more gain for a narrowband antenna over a wideband antenna when both are the same size. If you're reducing the frequency coverage from channels 14-51 to 14-36 but not changing the size, the 14-36 optimized antenna should have a little more gain. As always though, for the 14-36 antenna to have significantly more gain, it'll need to be much larger.
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post #18008 of 18323 Old 01-24-2020, 07:14 AM
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Quote:
Originally Posted by Calaveras View Post
Obviously that's true but that's not what I meant. There is a tradeoff for gain and frequency coverage for a given sized antenna. You can get a little more gain for a narrowband antenna over a wideband antenna when both are the same size. If you're reducing the frequency coverage from channels 14-51 to 14-36 but not changing the size, the 14-36 optimized antenna should have a little more gain. As always though, for the 14-36 antenna to have significantly more gain, it'll need to be much larger.
I agree.

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post #18009 of 18323 Old 01-24-2020, 07:24 AM
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Quote:
Originally Posted by rabbit73 View Post
Computer models give results in dBi, to compare the predicted performance of different designs.
They could just as well use dBd. I don't like dBi for the same reason most of the ham radio world doesn't use it. It's an antenna that can't be built and inflates the gain of real antennas.


Quote:
Originally Posted by rabbit73 View Post
Yes, but an antenna designed for the UHF band is usually modeled at a frequency at the center of the band. This will make the antenna less efficient at channel 14 which is away from the design frequency, causing the gain curve to fall at the low end. The gain curve will rise above the design frequency because the elements are longer than a halfwave.
After thinking about this for a couple of days I don't think this is true. I don't think the models consider the dipole factor at all. They simple model a configuration of pieces of metal over a frequency range in frequency steps.


Quote:
Originally Posted by rabbit73 View Post
My guess is that the antenna factor only needs to be considered when using the field strength in dBuV/m just before the signal touches the antenna (as in converting dBuV/m to dBm). The model includes the antenna factor because the antenna size is scaled to frequency and includes the feedpoint where signal power is measured.

dBuV/m to dBm calculator
http://www.g4axx.com/
click on Downloads
click on dBuV to dBm calculator (xlsx 20kB)

This conversion makes sense. Start with a 1 meter long antenna in an RF field of a certain strength (dBuV/m) and convert that to the actual signal the antenna will generate at its terminals.
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post #18010 of 18323 Old 01-24-2020, 07:43 AM
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Originally Posted by Calaveras View Post
They could just as well use dBd. I don't like dBi for the same reason most of the ham radio world doesn't use it. It's an antenna that can't be built and inflates the gain of real antennas.
Yeah, that's why QST doesn't allow gain figures in antenna ads.
Quote:
I don't think the models consider the dipole factor at all. They simple model a configuration of pieces of metal over a frequency range in frequency steps.
I understand your point.
Quote:
This conversion makes sense.
I couldn't find the link to the last converter I used; I like this one better.

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post #18011 of 18323 Old 01-28-2020, 08:55 AM
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The newest Channel Master LTE filter is listed as now going down to 600Mhz, passing 5 - 599Mhz. Which means right about at channel RF36. Not sure if it'll kill channel 36 or not, and I actually have a channel using that. I just ordered one at $19 and free shipping. Not sure how you can really TELL if LTE is affecting your antenna, but $19 isn't that bad to try it out.

https://www.channelmaster.com/TV_Ant..._p/cm-3201.htm
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post #18012 of 18323 Old 01-28-2020, 10:02 AM
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Originally Posted by Primestar31 View Post
The newest Channel Master LTE filter is listed as now going down to 600Mhz, passing 5 - 599Mhz. Which means right about at channel RF36. Not sure if it'll kill channel 36 or not, and I actually have a channel using that. I just ordered one at $19 and free shipping. Not sure how you can really TELL if LTE is affecting your antenna, but $19 isn't that bad to try it out.

https://www.channelmaster.com/TV_Ant..._p/cm-3201.htm
Something is not right. If they actually did change the filter, they should have changed the model number. They didn't change the model number of the 7777 preamp when they changed the design.

The description does say

Electrical Specifications

Frequencies Pass 5 - 599 MHz
Frequencies Block 600 - 2000 MHz

But if you look at the Product Sheet download it says:
LTE FilterSpecifications
Frequencies Pass: 5 - 699 MHz
Frequencies Block: 700 - 2000 MHz

That is correct for the 14-51 band.

If it really is 5-599, that would mess up 35 and 36.
35: 596 to 602
36: 602 to 608.

My test of the filter I bought:



If the CM-3201 filter has been redesigned to attenuate transmitters above channel 36, I would need to test it as I did previously. Just trying it out to see if it helps to improve reception isn't sufficient; it's not conclusive.

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post #18013 of 18323 Old 01-31-2020, 11:50 AM
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Originally Posted by Primestar31 View Post
The newest Channel Master LTE filter is listed as now going down to 600Mhz, passing 5 - 599Mhz. Which means right about at channel RF36. Not sure if it'll kill channel 36 or not, and I actually have a channel using that. I just ordered one at $19 and free shipping. Not sure how you can really TELL if LTE is affecting your antenna, but $19 isn't that bad to try it out.

https://www.channelmaster.com/TV_Ant..._p/cm-3201.htm
I received this in the mail today, a couple hours ago. It's the new version as pictured on the page above. Unfortunately, I can't install it right now. My antenna is on a 25' mast above my garage, and I have to get on the roof to install this. The roof still has 6" of snow and ice on it, and no way I'm going to try getting on that anytime soon. I can't take a fall from that height anymore. I do have a channel on RF36, WAQP, and LightTv is on .3, and we watch that. So, not sure if this filter will hurt my reception of that channel. I'll know once I can install it after a good melt.

Does anybody know what sort of interference, LTE can cause to signal levels? Not sure if I'm even having any issues I could attribute to possible LTE.

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post #18014 of 18323 Old 01-31-2020, 01:04 PM
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Quote:
Originally Posted by Calaveras View Post
If the overall antenna size is kept the same then optimizing will only produce a small gain increase. In order to get a significant gain increase the antenna will have to be much larger.

The impedance match would improve significantly, which is as important as gain and compounds the improvement.

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post #18015 of 18323 Old 01-31-2020, 01:23 PM
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Originally Posted by Primestar31 View Post
Does anybody know what sort of interference, LTE can cause to signal levels? Not sure if I'm even having any issues I could attribute to possible LTE.
If you have LTE interference, it is most likely to interfere with reception of UHF channels. It would probably affect signal quality rather than signal strength.

I see Light TV listed as a subchannel of WAQP:
https://www.rabbitears.info/market.p...&callsign=WAQP

This is a rabbitears.info report based on your location in 2015; I don't know if you have moved since then:
https://www.rabbitears.info/searchma...study_id=51721

Ideally, the filter should be inserted between the antenna and the preamp, but that wouldn't be safe to do now. You could try inserting it between the preamp power inserter and the tuner input as a test.

I'm still not convinced that CM has modified the filter for 14-36 reception.

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post #18016 of 18323 Old 01-31-2020, 01:38 PM
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Quote:
Originally Posted by rabbit73 View Post
If you have LTE interference, it is most likely to interfere with reception of UHF channels. It would probably affect signal quality rather than signal strength.

I see Light TV listed as a subchannel of WAQP:
https://www.rabbitears.info/market.p...&callsign=WAQP

This is a rabbitears.info report based on your location in 2015; I don't know if you have moved since then:
https://www.rabbitears.info/searchma...study_id=51721

Ideally, the filter should be inserted between the antenna and the preamp, but that wouldn't be safe to do now. You could try inserting it between the preamp power inserter and the tuner input as a test.

I'm still not convinced that CM has modified the filter for 14-36 reception.
We did move 2~ miles South-East of our old house in the woods, and signal levels are a bit better than the old house in the middle of the woods. I'm still using a Y10-7-13 antenna for WJRT-12 which is RF12, and a HDB91x for all my UHF channels. They are on a 25' mast pipe setup.

The Y10-7-13 goes through a MCM Electronics FM filter, then into the VHF side of a Radio Shack UVSJ. The HDB91x is pointed at WEYI-25, which is basically the center of the arc for UHF towers, and almost directly in a line beyond the low powered stations WFFC-LD & WFKB-LD. That goes into a Kitztech KT200-Coax preamp, then into the power passing UHF side of the Radio Shack UVSJ. Then Rg-6 quad-shield coax to my Tivo and tv set.

I get all my channels pretty solid, including the two low powered ones WFFC-LD & WFKB-LD, which are 32~ miles from me, as the crow flies.

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post #18017 of 18323 Old 01-31-2020, 02:45 PM
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Quote:
Originally Posted by lifespeed View Post
The impedance match would improve significantly, which is as important as gain and compounds the improvement.

That's possible but it's not a guarantee. The SWR has to be pretty bad to impact the gain much. An SWR of 2.0 has a mismatch loss of 0.5 dB, SWR of 2.7 has a mismatch loss of 1.0 dB and an SWR of 3.0 has a mismatch loss of 1.25 dB. Above 3.0 the mismatch loss climbs rapidly. It's a pretty bad antenna that has an SWR above 3.0. An SWR improvement of 3.0 to 2.0 only picks up 0.75 dB.
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post #18018 of 18323 Old 01-31-2020, 03:07 PM
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Quote:
Originally Posted by Calaveras View Post
That's possible but it's not a guarantee. The SWR has to be pretty bad to impact the gain much. An SWR of 2.0 has a mismatch loss of 0.5 dB, SWR of 2.7 has a mismatch loss of 1.0 dB and an SWR of 3.0 has a mismatch loss of 1.25 dB. Above 3.0 the mismatch loss climbs rapidly. It's a pretty bad antenna that has an SWR above 3.0. An SWR improvement of 3.0 to 2.0 only picks up 0.75 dB.

Plus the interaction with the SWR of the tuner, plus a slight improvement in gain. While 0.75dB is a small number, in linear power that's nearly 20% more. Let's say the antenna re-tuning nets you better match and better gain to the tune of 1.5dB total, probably a reasonable estimate. That's 41% more power to the tuner, something that is easily noticeable by a viewer with a marginal signal strength/quality station.


It won't be a miracle, but it could easily be noticed. The only obstacle is the manufacturer's applying their cost/benefit analysis. Are people still buying their old-design antennae, or will the first one to market with an optimized design gain market share from savvy buyers? Over in the UK they've already designed a nice Yagi called XB16A that coincides with our new UHF band. I'll probably replace my 91XG with one of these when I feel the need to bring the mast down for rework to add VHF reception for the SF bay area repack and ATSC 3.0 Silicondust tuners. Which don't exist yet.

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post #18019 of 18323 Old 01-31-2020, 03:39 PM
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Quote:
Originally Posted by Primestar31 View Post
We did move 2~ miles South-East of our old house in the woods, and signal levels are a bit better than the old house in the middle of the woods. I'm still using a Y10-7-13 antenna for WJRT-12 which is RF12, and a HDB91x for all my UHF channels. They are on a 25' mast pipe setup.
Thank you for the coordinates for your better OTA location. Here is a new report:
https://www.rabbitears.info/searchma...study_id=51782



and here is a new FM report, but I don't know how accurate it is:
http://www.fmfool.com/modeling/tmp/3...3/Radar-FM.png
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post #18020 of 18323 Old 02-01-2020, 12:00 AM
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Does anybody know what sort of interference, LTE can cause to signal levels? Not sure if I'm even having any issues I could attribute to possible LTE.
LTE interference is an issue, obviously, because the 600, 700 and 800 MHz cell bands used to be part of the UHF TV spectrum. Hence, antennas and amplifiers do a good job at receiving them.

When you're close enough to a cell tower (1-2 mi or less), the level is strong enough that it can overload the amplification in your system (particularly high gain preamps).

In mild cases, it degrades the signal-to-noise ratio, but not enough to cause breakups.
In moderate cases, you'll notice random dropouts.
In severe cases, it will completely wipe out reception of a channel, as the signal-to-noise ratio drops completely below the decoding threshold.

The easiest way to tell (save for a spectrum analyzer) is simply to install an LTE filter before the first amplification stage and see what difference it makes, if any. Usually in the presence of LTE overload, the signal meter readings on a TV will jump around wildly, whereas you'd normally see very slight changes from moment to moment.

One example case from my files: 45 mi from both full-power and 15kW LP stations, running a preamp and UHF/VHF-Hi yagi's on the roof - LTE tower 75 degrees off-axis, probably 1 mi away. Without an LTE filter, full-power's all scanned in strong (but not stable) level, some LPs were exhibiting constant breakups, some didn't scan in. Installed LTE filter, SNRs improved across the board - full-power's are stable, all LPs scanned in with none breaking up, including a weaker station that had previously not scanned sitting at a stable 17dB SNR.

Not a universal rule, but I've observed LTE interference worsen in the evening, presumably as the network is more congested.

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post #18021 of 18323 Old 02-01-2020, 05:00 AM
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I'm about 2.5 miles away from my closest LTE tower, and I have to aim nearly right through it on a bearing to get all my UHF stations. I don't get any wild signal swings or dips, but on my couple of lower power stations, (WFFC & WFKB) I get slight audio dips frequently. Enough to be a little annoying. Though those are broadcasting from the same tower 32 miles away, owned by the same company. So perhaps those audio dips are an artifact of their transmission. It's hard to say.

Those two stations are broadcasting on RF17 and RF19 respectively though.

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post #18022 of 18323 Old 02-03-2020, 04:09 PM
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Originally Posted by Primestar31 View Post
I received this in the mail today, a couple hours ago. It's the new version as pictured on the page above. Unfortunately, I can't install it right now. My antenna is on a 25' mast above my garage, and I have to get on the roof to install this. The roof still has 6" of snow and ice on it, and no way I'm going to try getting on that anytime soon. I can't take a fall from that height anymore. I do have a channel on RF36, WAQP, and LightTv is on .3, and we watch that. So, not sure if this filter will hurt my reception of that channel. I'll know once I can install it after a good melt.

Does anybody know what sort of interference, LTE can cause to signal levels? Not sure if I'm even having any issues I could attribute to possible LTE.
Ok, I just tried the new LTE filter on the back of my 2013 LG tv set after a PM I received from another person here that mentioned trying it that way. It did NOT drop signal or quality level on WAQP-49, which broadcasts on RF36. Checking all my other receivable channels, it didn't affect any of them adversely as far as I can tell, and the two low powered ones WFFC & WFKB seemed to have come UP a couple points. It only took me about a minute to screw the filter on, so atmospheric changes shouldn't have affected anything that quickly.

So, that at least gives me hope that once I can install it at the output of my actual antenna, and before the Kitztech KT-200 preamp, that I don't have to worry about it killing WAQP's signal, or even dropping it enough to cause issues with reception.

Question: Can LTE transmissions affect any tv channels BELOW RF36~, if the tower is close enough to you, say within 1 mile? Not sure if subharmonics can apply to LTE broadcasts.

Last edited by Primestar31; 02-03-2020 at 04:46 PM.
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post #18023 of 18323 Old 02-03-2020, 07:06 PM
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The LTE signal itself is not the issue - it is (we presume) filtered and strictly limited to its allocated frequency spectrum, otherwise the cell carrier has defective equipment/engineering and is in violation of FCC rules.

The issue is when it enters an amplifier at a strong enough level to be driving the amp into overload. The amp starts clipping, intermodulating, creating images/subharmonics, you name it. In an amp with separate UHF/VHF stages, it will likely only affects only UHF (all UHF channels - both above and below 36), but it could probably trash VHF too on a single stage amp. It's seen more on weaker channels and it may be worse depending on the frequency - YMMV.

I have personally witnessed the Kitztech's overloading from LTE.
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post #18024 of 18323 Old 02-03-2020, 07:49 PM
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Originally Posted by mattdp View Post
The LTE signal itself is not the issue - it is (we presume) filtered and strictly limited to its allocated frequency spectrum, otherwise the cell carrier has defective equipment/engineering and is in violation of FCC rules.
How do you go about proving that a cell company is in violation? And what can you actually do about it? Seems to me, cell companies rule the spectrum and get what ever they want. Interfering with someone's TV reception is the last thing they care about.
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post #18025 of 18323 Old 02-03-2020, 08:29 PM
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For the record, every case of cell interference I've dealt with was fixed by installing a filter prior to the first amplifier. It's the consumer receiving equipment (in the presence of strong cell signal), not the cell signal itself causing the issue.

I have never heard of a case of a cell tower spewing garbage out-of-band. They've got pretty sophisticated monitoring systems, not to mention teams of engineers that do design & monitoring. Other cell carriers in the area and probably TV stations would be affected too.

But... let's say you did actually have a cell site that was malfunctioning. You'd take a directional antenna and spectrum analyzer to isolate the tower in question and actually observe said out-of-band interference. Photographs, videos and other documentation will certainly help your case. I'd first contact the operator of said site and explain the situation. I would presume they would be highly motivated to fix the issue. If, for whatever they were delinquent in addressing it, then I would level a complaint with the FCC - who could levy all kinds of fines and whatnot.
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So, I'm confused. Does the LTE interference potentially affect all users with OTA antennas or only for users who are using amps on their antennas?
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post #18027 of 18323 Old 02-03-2020, 08:56 PM
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LTE interference can affect anyone using OTA, with or without amplification.

In my experience as an installer, I find it's mostly an issue when using high gain preamps in close proximity to cell towers. But if you're close enough, it could potentially swamp out the IF in the receiver.

I've got a spectrum analyzer, so I know for sure if/how much of an issue it is. For the average consumer, testing with/without a filter is really the only practical way to tell for sure. At $20 and with little insertion loss, it really isn't going to hurt to have one in-line and not "need" it/
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post #18028 of 18323 Old 02-04-2020, 10:28 AM
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Matt... I just read your antenna installation guide and wanted to compliment you on the nice, easy to read and understandable writing... nice job!

Larry

My complete SF Bay Area DTV Station Lists: http://www.larrykenney.com/sfonair.html
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post #18029 of 18323 Old 02-04-2020, 10:52 AM
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Quote:
Originally Posted by mattdp View Post
For the record, every case of cell interference I've dealt with was fixed by installing a filter prior to the first amplifier. It's the consumer receiving equipment (in the presence of strong cell signal), not the cell signal itself causing the issue.

I have never heard of a case of a cell tower spewing garbage out-of-band. They've got pretty sophisticated monitoring systems, not to mention teams of engineers that do design & monitoring. Other cell carriers in the area and probably TV stations would be affected too.

But... let's say you did actually have a cell site that was malfunctioning. You'd take a directional antenna and spectrum analyzer to isolate the tower in question and actually observe said out-of-band interference. Photographs, videos and other documentation will certainly help your case. I'd first contact the operator of said site and explain the situation. I would presume they would be highly motivated to fix the issue. If, for whatever they were delinquent in addressing it, then I would level a complaint with the FCC - who could levy all kinds of fines and whatnot.
I contacted the FCC about a local pirate FM station. It took over a year for anything to happen. Nobody ever followed up with me. I'm not even sure it was my complaint that led to any action. And after some searching I found they'd been shut down multiple times before only to pop up on another frequency. So I don't have much faith in the system.
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Quote:
Originally Posted by labjr View Post
I contacted the FCC about a local pirate FM station. It took over a year for anything to happen. Nobody ever followed up with me. I'm not even sure it was my complaint that led to any action. And after some searching I found they'd been shut down multiple times before only to pop up on another frequency. So I don't have much faith in the system.
You did the right thing. The FCC resources are budget limited; their effort must be prioritized.

If you can not measure it, you can not improve it.
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