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post #1 of 12 Old 11-09-2017, 07:02 AM - Thread Starter
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Oley,PA: LTE Filter Placement

I determined that I need an LTE filter since I recently started having interference on channel 12 each evening from about 6PM to 10PM. A new cell tower is less than 2 miles from my house and is visible. i understand that these are the peak hours for cell usage. Other channels are not affected but have stronger signals. I have a Winegard 8200 antenna on the roof with a Winegard LNA 200 pre-amp. I get stations from 4 directions with a rotor. Can I just place the filter between the cable and the TV's antenna input or must it go by the pre-amp? I'd rather not go on the roof if possible.
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post #2 of 12 Old 11-09-2017, 07:19 AM
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post #3 of 12 Old 11-09-2017, 07:36 AM
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It needs to go between the antenna and the preamp.
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post #4 of 12 Old 11-09-2017, 09:12 AM
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It is assumed you are referring to the PBS station out of Philly, WHYY on real and virtual channel 12.

It is about 99.9% likely that your diagnosis of LTE interference is incorrect. There's simply no way that 700 MHz signals are going to disrupt a VHF channel 12 with the pre-amplifier you have in use. It's front end has a U/V diplexer circuit that will attenuate UHF and LTE signals by > 30 dB before the VHF signals are amplified. Another U/V diplexer is on the output to re-combine the separately amplified frequency bands before sending the signals down stream. However, if you want to try the filter if you've already ordered it, it can go anywhere in the distribution scheme as long as it does not block operating power between the amp and its power inserter. Additionally, 700 MHz signals are not going to cause interference into other frequencies that are less than a third of the frequency of the wireless system. If they do, there's either a fault in the system or something is very poorly designed and implemented, probably on the receiving end.

Since your issue is in the evening hours, it's far more likely that you have a local electrical, electronic or lighting interference issue.

If not for that amp's dual signal path configuration, then Chuck's suggestion would indeed be spot on assuming the intermods occur in the amp. Of course, they could always be occurring in a tuner, also.

In any event 700 MHz signals at two miles is extremely unlikely to be strong enough for interference concerns anyway unless you had both a high gain UHF antenna aimed dead at the tower plus a high gain preamp. The power levels coming off cell towers isn't all that strong at that distance.

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post #5 of 12 Old 11-09-2017, 01:56 PM
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I agree 100% with ADTech but since you started your post with "I determined" I took you at your word that you were 100% positive what the problem was and all you needed to know was where to put the filter.

The truth is that cell traffic has nothing to do with the potential for interference. Cell transmitters are on the air 24 hours a day. They are not like public service repeaters that are only on the air when in use. If the cell was your problem then you'd have interference all the time.

Attached is a spectrum analyzer display of my local T-Mobile, AT&T and Verizon 700 MHz LTE transmitters. The look of the signals continually varies but the transmitters never go off the air. Same goes for all the other cell bands.
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post #6 of 12 Old 11-11-2017, 06:22 AM
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When I had intermittent issues on real and virtual channel 12 (WJRT) in my area a few years back, I tracked it down to TWO things with Rabbit73's help in suggesting to use an AM radio as a tracker:

1: A Harbor Freight car battery tender in my garage. That sucker broadcast interference more than 300 ft OFF my property! My antenna and preamp didn't have a chance against this sort of interference. I removed it from service since it has no shielding.

2: My Dell laptop power brick which was in the living room by the tv set. I threw it away, and replaced it with a new one that wasn't faulty.

I also suggest your issue is likely something like this. Electrical interference of this type is insidious, and can be very hard to figure out what's causing it. But once you are aware that's a possibility, it's a matter of methodically tracking it down.
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post #7 of 12 Old 05-03-2018, 12:06 PM
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Quote:
Originally Posted by Calaveras View Post
It needs to go between the antenna and the preamp.
Calaveras, just curious - why are you recommending that the LTE filter be placed before the preamp?
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post #8 of 12 Old 05-03-2018, 01:22 PM
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Calaveras isn't here at the moment, but I will try to answer; he can correct me if I am wrong.

1. The filter must go before the preamp because it is more sensitive to overload than a tuner. The difference is approximately equal to the preamp gain.

2. The tuner has tuned circuits that allow the selected channel to pass, and other frequencies are rejected; a preamp is wide open to many frequencies at its input and all of then are amplified.

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post #9 of 12 Old 05-03-2018, 01:30 PM
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There's a fairly substantial power difference between an idle LTE signal and one that's fully loaded with traffic. More than 10 dB. The pilot carriers are always present, but the data carriers are only active when there's traffic. The number of active data carriers depends on the instantaneous amount of traffic.


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post #10 of 12 Old 05-03-2018, 04:11 PM
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Quote:
Originally Posted by rabbit73 View Post
Calaveras isn't here at the moment, but I will try to answer; he can correct me if I am wrong.

1. The filter must go before the preamp because it is more sensitive to overload than a tuner. The difference is approximately equal to the preamp gain.

2. The tuner has tuned circuits that allow the selected channel to pass, and other frequencies are rejected; a preamp is wide open to many frequencies at its input and all of then are amplified.

Yes, I second this.
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post #11 of 12 Old 05-03-2018, 04:22 PM
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Quote:
Originally Posted by dr1394 View Post
There's a fairly substantial power difference between an idle LTE signal and one that's fully loaded with traffic. More than 10 dB. The pilot carriers are always present, but the data carriers are only active when there's traffic. The number of active data carriers depends on the instantaneous amount of traffic.

That explains why I see continually varying displays on the local LTE signals. The display looks different on every analyzer sweep.
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post #12 of 12 Old 05-03-2018, 04:43 PM
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Thanks everyone for your response, makes sense.

I think it's time to give the filter a try. I have been seeing quite a variance in signal quality in channels RF34 and above recently.
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