Very odd behavior (OTA TV & Scanners)

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kb7gjy

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Had this setup for years and never had a problem. Scanner just hums along no issues, TV worked great.

Last weekend I I change channels on the TV and the channel is very poor, signal strength is very low. Odd... I checked with the inlaws less then 500 yards away, no problem with that channel and Scanner is just doing great (They are ran through a combiner and have for years with no issues).

Ok, I climb my tower and check connections, all looks fine, antenna is pointing at the translator site (14 miles away clear line of site). climb back down. Nope still poor signal on that one channel. The translator has one or two channels on UHF the rest is VHF.

Hmmmm, maybe coax, its been up there for years but was sealed properly. Replaced coax with double shielded 75 ohm. clean contacts.

Same problem. Grrr. change to my backup antenna at ground level. same problem. Now I'm really confused. Check other TV and it only shows poor signal on that one channel. Take combiner out and go direct to TV, same problem on both TVs. Obviously scanner stopped receiving when disconnected.

I sit down and crack open a beer as I missed my program I wanted to watch. Everything reconnected. I leave the TV on the poor signal channel scratching my head.

Then my wife walks over and opens the sliding glass thermal window. POOF, signal jumps up comes in clear as a bell. All channels are totally fine. I asked her to close the window. The signal drops to nil. again only on that one channel. Open window signal jumps back up

Coax isn't anywhere near that window, comes down the tower enters the house through ice shield to eve 6 feet away from the window.. Antenna is 35' above the window on the tower.

I have helped design and install public safety systems, repeaters on mountain tops, dispatch centers, upfit ambulances and patrol cars, yet this one channel only reliably works with the ()*&^%#*&%(&^)*^* window open. I'm also on the Translator board so I know the physical freqs of the channels. Nothing has changed at the translator. My scanner is monitoring PS freqs on both VHF and UHF.

WHAT AM I MISSING????? (and no, I can't just leave the window open, wife gets upset in the winter in far north Idaho with the window open)

Changed coax, swapped antennas, nothing has changed at translator site. I even installed a mast mount preamp, didn't help. I'm sure it is something stupid I'm missing.

Ideas?

Scanner just keeps humming away, no issues.
 

tvengr

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Does this happen when the sun is shining? I had a case with an electronic organ where the volume always dropped to nothing at a certain time of day. It ended up that at that time of day, the sunlight hit the light dependent resistor on the expression pedal that controls the volume. If your TV has a LDR, opening and closing the window could affect its operation. If your windows have a film applied to block sunlight, I believe that film is conductive and blocks RF signals. It could also reflect an interfering RF signal. I also had a monitor from a TV live truck that the techs said the color phase was off. Every time the techs brought the monitor to the shop, I could find nothing wrong. I ended up going down to the truck and found that when I opened the lid on the top of the equipment rack, the color changed. The rack had become magnetized. On a problem like yours, you have to forget what you know and think outside of the box. Look for anything else in the room, including your scanner, that could be radiating an interfering signal. The 2 TV's could be interfering with each other. Is the window connected to an alarm system? The alarm system could radiate a signal. The alarm wiring would make a great antenna. Has anything in the house been changed at the time your trouble started? Do you have any new appliances? I hope this changes your thinking to look for something other than the obvious. Good Luck!
 
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Ubbe

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Backup antenna did not work. New coax and removing combiner did not help. What is that translator thing? Is it changing the recieved tv channels frequencies to another frequency?

Look up that troublesome tv channels frequency and set the scanner to WFM or at least FM with the squelch open and tune to the tv channels audio carrier that are 4,5MHz up from the start frequency of the channel. Then listen to the audio while opening and closing the window slowly.

Does the signal degrade slowly or does it suddenly drop at a certain point when the window are closing? Try position the window just when the signal has dissapeared and try other things in the room or the installation to see if there's a signal change when you touch anything else.

If you can stream the scanners audio, easily done with a BCD536, then listen to the stream with a mobile phone or pad and go outside and touch and move objects near the coax and antenna.

/Ubbe
 

jonwienke

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Get a SDR dongle like the $21 rtl-sdr on Amazon, a 10-foot usb extension cable, download and install on a laptop, and do some signal sniffing. It's much easier to use tle bandscope display in SDR# than a 5-segment signal meter to see the offending signal, and track it down.
 

u2brent

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Backup antenna did not work. New coax and removing combiner did not help. What is that translator thing? Is it changing the recieved tv channels frequencies to another frequency?
/Ubbe

A "Translator" in North American OTA terminology is a Low Power (usually) Repeater sometimes on a different ch re-transmitting the original broadcasters signal.
 

Ubbe

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It could be the same phenomen as with simulcast, if that translator site use the same frequency as the original site.

The roof antenna receives both the original site and translator site and the signals cancel each other out. When opening the window you only increase the signal from the translator and not from the original site that cannot be recieved at ground level. Probably a test with a paper clip as antenna would prove if it is that cancelling problem.

/Ubbe
 

jonwienke

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No. Translators are not on the same frequency, for the simple reason that consumer TV and FM broadcast doesn't have SDR I/Q tuners to filter simulcast.
 

Ubbe

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And also the tv and/or coax installation must have some huge RF leakage to receive anything through the window. But the whole thing seems very strange so monitoring signal level changes while touching things nearby the window seems like a feasible method.

/Ubbe
 

kb7gjy

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I ordered a few LTE filters to add to the TV inputs as it is possible solution. The physical channel is 46.3 and 46.4 (Compared to the displayed channel of 28-1 and 28-2).

I have a 4G cell phone booster, which I have had for years. So I turned it off/removed power and waited 10 minutes, no change on TV reception, still poor. Turned back on, still no change

So to date, I have now bought a new antenna (100 mile range RCA brand VHF/UHF). new feedline, used separate inputs for VHF and UHF (Two antennas), combined (two antennas into one input), Only a single antenna w/ and w/o mast mount preamp (signal got a little worse w/o preamp). I will do some sniffing with my SDR around 660 MHz to 680 MHz to see if I can find anything that is interfering.
 

majoco

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What is the window frame made from? Aluminium? I'm suspecting a multipath signal - one direct from the TV transmitter and another reflected from the window frame to the antenna are in antiphase and cancelling each other out. With the transmitter only 14 miles away perhaps your problem is too much signal - try just a simple dipole - possibly not even the right length for a trial.

Reading through your original post again.... what is a "thermal" window, does it have some kind of reflective coating on it? If it's a metal deposited on the glass you may have a very good RF reflector right there!
 
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217

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Low emissivity glass contains metal a coating that blocks most electromagnetic radiation from passing through the glass, minimizing the amount of ultraviolet and infrared radiation (heat energy) that enters the building, while still allowing visible light to pass through.

There are even certain types of low‑e glass are specifically used to block all RF signals, including cell signals, to prevent transmission into or out of the building. This type of glass is used in highly-secure buildings.
 

wa9cat

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Is the channel you are trying to receive operating temporarily on low power
Numerous tv stations are changing to new antennas across the country. Check their web site At some point near the end of oct you will have to rescan your tv for the over the air signal because they are changing freq. are you aware of that?
 

kb7gjy

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What is the window frame made from? Aluminium? I'm suspecting a multipath signal - one direct from the TV transmitter and another reflected from the window frame to the antenna are in antiphase and cancelling each other out. With the transmitter only 14 miles away perhaps your problem is too much signal - try just a simple dipole - possibly not even the right length for a trial.

Reading through your original post again.... what is a "thermal" window, does it have some kind of reflective coating on it? If it's a metal deposited on the glass you may have a very good RF reflector right there!
Low emissivity glass contains metal a coating that blocks most electromagnetic radiation from passing through the glass, minimizing the amount of ultraviolet and infrared radiation (heat energy) that enters the building, while still allowing visible light to pass through.

There are even certain types of low‑e glass are specifically used to block all RF signals, including cell signals, to prevent transmission into or out of the building. This type of glass is used in highly-secure buildings.

The window is vinyl, nothing high tech, been there for years.

Is the channel you are trying to receive operating temporarily on low power
Numerous tv stations are changing to new antennas across the country. Check their web site At some point near the end of oct you will have to rescan your tv for the over the air signal because they are changing freq. are you aware of that?

Power at the site has not been modified in any way nor any channel reassignments. No antennas or feedlines or other related equipment has been changed. To my knowledge, we do not have pending reassignments as we already made the changes months ago to no longer be on T-Mobile's frequencies they now have after the auction.

I did have a older antenna I tried (Indoor style) and tried it directly to the TV. It is a VHF/UHF. Resulted in loss of all channels regardless if the window was open or closed, nor placement of the antenna around the room or near the window. I'll try it outside the next opportunity I get to

I didn't have a chance to use the SDR to do sniffing around yet, just had to much on my plate this weekend.
 

jonwienke

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IMO, sniffing with the SDR is going to be the key to solving the mystery.
 

krokus

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IMO, sniffing with the SDR is going to be the key to solving the mystery.

I second this.

I am wondering if there is some sort of IMI, due to corroded metal near that window. The window could be changing the contact point, either opening the bad contact, or closing a shunt. (Siding, alarm system contacts, etc.)
 
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