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Old 8-Nov-2017, 2:00 AM   #1
Spongebob
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Join Date: Sep 2017
Location: Central VA
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Strong VHF Signal - No Picture

I have a Winegard HD8200U installed in the attic. All the local stations have excellent signal strength, but Channel 3 (real) (15 Virtual) does not appear when the TV scans for stations.

Using the Emitor DigiAir Pro ATSC meter, channel 3 yields a 58 dBuV signal strength. However, the BER and SNR readings will not lock.

The engineer at the station suggests that the ATSC pilot at 60.31 MHz is not being seen by the TV's tuner.

Upon the advice of Sven at Emitor, I have now installed 4 LTE filters at the antenna and was able to receive the station for a short period of time, but not consistently. Another LTE filter is on order.

A cell tower is located approximately .7 mile from the house.

The antenna has been moved both horizontally and vertically as well as rotated.

Any thoughts as to other actions to take ?

Bob
Central VA
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Old 8-Nov-2017, 4:14 AM   #2
rabbit73
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Welcome, Bob

Is the coax grounded to the house electrical system ground using a grounding block?

Ordinarily, a grounding block is not required for an indoor antenna, but strong signals can buypass any filters and directly enter the TV cabinet if the coax isn't grounded.

What does your TVFool signal report look like?

It could be FM interference to VHF. What does your FM Fool signal report look like?

Is the channel WBRA?

Loss of the pilot can be caused by multipath reflections.

This signal will not lock because of too many errors (high BER) even though it is fairly strong; -12.7 dBmV = 47.3 dBV.



A 58 dBV signal is strong. Are you using an amp?
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Last edited by rabbit73; 8-Nov-2017 at 2:33 PM.
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Old 8-Nov-2017, 12:25 PM   #3
ADTech
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It would seem (to me) that it would be HIGHLY unlikely that LTE frequencies would have any effect on the reception of a VHF 3 signal. In any event and assuming that you're buying and installing the CM3201 filter, those have > 40 dB rejection at about 730 MHz, the start of the most commonly used LTE blocks. A 700 MHz LTE signal, assuming ATT or VZN, isn't going to have signal strong enough at 3/4 of a mile to make it through even ONE of those filters, much less four or five of them.

I'd suspect something far less exotic, like a local lighting product or other electrical device in or very near the house is causing the interference.

Getting the antenna out of the attic and up into the air would likely do wonders.

Unfortunately, your DigiAir meter isn't going to be able to do much for you since you really need to be able to see the spectrum with a much narrower bandwidth around channel 3. It appears to only allow a spectrum display of its full channel span.
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Last edited by ADTech; 8-Nov-2017 at 4:54 PM.
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Old 8-Nov-2017, 2:13 PM   #4
rabbit73
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I agree with ADTech.

LTE interference is not likely, but electrical interference to VHF-Low channel 3 is very possible.

Try searching for electrical interference noise with a battery operated portable radio for the AM broadcast band. An FM portable radio is not as good for this test.

Electrical interference on the AM broadcast band is often strong enough to also affect VHF TV signals. The interference raises the noise floor, which will reduce the SNR of the channel 3 signal.

Tune to an unused frequency first at the low 540 kHz end and then the high 1600 end. The antenna in the radio is directional, which can help you locate the source of the possible interference.

Is the problem constant, or related to certain times of the day?

Possible sources of electrical interference are CFL and LED lamps, motors, battery chargers, switchmode AC to DC power adapters, inverters, street lamps, and power lines.
Quote:
A cell tower is located approximately .7 mile from the house......The antenna has been moved both horizontally and vertically as well as rotated.
What is the azimuth for the cell tower, what is the azimuth for channel 3, and how far away is the channel 3 transmitting tower?
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Last edited by rabbit73; 8-Nov-2017 at 3:21 PM.
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Old 9-Nov-2017, 1:45 AM   #5
Spongebob
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Location: Central VA
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Thanks for the excellent replies. I will work on your suggestions one by one and hopefully find a solution.

"Ordinarily, a grounding block is not required for an indoor antenna, but strong signals can bypass any filters and directly enter the TV cabinet if the coax isn't grounded."

I've not installed a grounding block ... yet. Will do so next.

"It could be FM interference to VHF"

I have installed an FM filter as well as the LTE filters.

"Loss of the pilot can be caused by multipath reflections. "

This may be the most likely problem.

"Is the channel WBRA?"

Yes

"Unfortunately, your DigiAir meter isn't going to be able to do much for you since you really need to be able to see the spectrum with a much narrower bandwidth around channel 3. It appears to only allow a spectrum display of its full channel span."

I am making arrangements to borrow a spectrum analyzer.

"Is the problem constant, or related to certain times of the day?"


The problem is constant, but there have been random windows of reception in the evening hours.

... how far away is the channel 3 transmitting tower? "

I'm approx. 50 miles from the transmitting tower.

"Getting the antenna out of the attic and up into the air would likely do wonders."

I constructed a folded dipole antenna for Channel 3. It works great at a different location. However, at this particular location, moving it around the yard produced the same results as the big Winegard in the attic ... great signal but the BER would not lock.

I'll continue to work on the dilemma and report back.

I really appreciate all of the input.

Bob
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Old 9-Nov-2017, 2:49 AM   #6
ADTech
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Your experiment with the dipole would, to me, tend to support the suspicion of local interference. The spectrum analyzer is the right tool to see if you can solve the mystery.
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