Bizarre reception issues - what's the science behind them? - Canadian TV, Computing and Home Theatre Forums

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post #1 of 13 (permalink) Old 2019-05-21, 07:40 PM Thread Starter
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Bizarre reception issues - what's the science behind them?

I have an indoor antenna mounted in my basement feeding into an Antronix MVRA501B and then out to two TVs - one in the basement and one on the second floor.

Vertically orienting the antenna one way I get n channels with no reception issues. So far, so good.

Rotating it 90° counter-clockwise I get n+3 channels but reception on the 2nd floor TV gets flaky.

Examples:
1. A particular channel looks pixellated, so my wife lowers one of three blinds on the bay window in the dayroom. Pixellation cured.

2. She's watching TV on a different channel, I close the door on the adjacent home office, the image pixellates. Open the door, everything's fine.

What the...?!

If the antenna two floors down is picking up the signal and feeding it to the TV via a shielded coax cable, how do a blind in the dayroom and a door on the adjacent room affect the signal?
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post #2 of 13 (permalink) Old 2019-05-21, 08:43 PM
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The basement is the worse place to put an antenna. Consider moving it to the second floor. The attic would be even better. Outside above the roof better still.

Most TV signals are horizontally polarized. Placing the antenna in that orientation will work best. Most antennas are directional to some degree so turning it will change reception. Experiment or refer to TVFool to find the direction that works best. Posting a TVFool report link will help others help you.

There is nothing bizarre about these results. There are many factors that affect reception. Those include signal strength and multipath (caused by reflections.) There are lots of factors that can affect both, including the location and orientation of objects, buildings, trees, animals and people. Locating the antenna so that they don't affect reception is the key. Think of TV reception as being a little like sight. If you want to see something on the horizon, you need a good, high location. To some extent, radio wave act the same way.

In addition, refer to the OTA reception results thread for your location.
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post #3 of 13 (permalink) Old 2019-05-21, 11:33 PM
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Indoor reception typically consists of MANY signal components, perhaps coming from a different direction into your house, such as direct thru the wall....or window...plus Reflections....plus Diffraction off Top of Side from surrounding Buildings & Terrain (might even be behind you). The signal level of each Incoming Multipath will typically vary, as will the amount of Loss encountered between the entry point and your Antenna. However, many times the Incoming Signals will NOT have a low loss path directly into your Indoor Antenna and will need to REFLECT off of something in your house (more Loss) before being received by your Antenna.

More and more stations are adding a second Transmitter and Antenna to broadcast either a Circularly or Elliptically Polarized signal (esp. if intended to be ATSC 3.0 Transmitter to many Mobile Receivers). Reflections can selectively attenuate either the Vertical or the Horizontal component...so it's a crap shoot whether the signal you recieive on EACH Channel in your home is primarily Vertically or Horizontally Polarized. So IF station is broadcasting Polarized signal, you might get marginally better reception by positioning VHF Rabbit-Ears at 45-deg Angle since that has equal reception of Vert. and Horiz. Polarized signals, as well as up to 3 dB higher Gain for Cir. Pol. signals.

Fol. describes various INDOOR physical processes that result in signals bouncing all around your house:
https://pdfs.semanticscholar.org/6ab...446.1558494465

Fol. illustrates various Multipath Signal Components (Diffraction may be around the SIDE of an intervening Building):


Fol. illustrates how many signal paths may be getting from Entry Point (say a Window) to Receiver:


TV Signal Strength in a Typical Room depends on LOCATION, LOCATION, LOCATION:
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Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #4 of 13 (permalink) Old 2019-05-25, 11:25 AM Thread Starter
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Thanks for the input. I understand the points made about line-of-sight, reflections and multi-pathing. But it's still not clear to me how lowering a blind or closing a door on the second floor of our house interferes with the otherwise successful reception of signal by the antenna two floors down.
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post #5 of 13 (permalink) Old 2019-05-25, 01:45 PM
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Quote:
Originally Posted by eljay View Post
.....it's still not clear to me how lowering a blind or closing a door on the second floor of our house interferes with the otherwise successful reception of signal by the antenna two floors down.
If the antenna is in the basement, that means the signals are coming to the antenna from above. Anything you do above, including the presence of your body, will be in the signal path and affect reception.

The solution is to move the antenna HIGHER, above anything that would be in the signal path.

Your reception results are trying to tell you that you can't ignore the natural laws. You might WANT the antenna in the basement, but the antenna needs to be located where the best signals exist for reliable reception.

The best location for my indoor antenna was in the middle of the bedroom floor, by the bed, in a high traffic area (of course it was). I finally found the second-best location in the corner of the bedroom.



A chair in front of the antenna hides the 5 gal Home Depot bucket.

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2019-05-25 at 03:11 PM.
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post #6 of 13 (permalink) Old 2019-05-25, 02:56 PM
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If a room has a window in the general direction of the station, next to the window is often the best choice. That's because glass blocks signals less than other building materials. It still needs to clear local outside obstacles that might block the signal. If a building has a lot of metal, it will block signals if in the path or reflect them if to the side or back. As already noted, signal paths can often cause hot spots or dead zones. That's because reflection, diffraction and absorption can cancel or reinforce signals.

Quote:
But it's still not clear to me how lowering a blind or closing a door on the second floor of our house interferes
As the antenna is in the basement, those objects may be reflecting the signal to the basement. That would be most likely if the blinds or door contain metal. I've seen signals seem to appear and disappear just by walking across a room. A common phenomena occurs when someone adjusts an indoor antenna for best signal and then steps away from the antenna and the signal disappears. That's because the person formed part of the antenna while standing close to it.
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post #7 of 13 (permalink) Old 2019-05-25, 03:50 PM
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Originally Posted by eljay View Post
FWIW, I bought one of those (Antronix MVRA501B amp) on-line from a place somewhere in the GTA (IIRC) and it work great to get signal...
- from my small indoor OTA antenna (Clearstream Eclipse unamplified) in the basement at the front of the house;
- through existing cabling;
- to a TV at the back of the house.

Future plans include connecting the existing cable that runs up to the dayroom / guest bedroom on the second floor to stream OTA to the TV in that room.
Which channels are you having trouble with? That antenna might not be the best choice for your location even with the added amp.

The basement location of your antenna is far from optimum. It is not unexpected that your reception has problems.

What does your TVFool signal report look like? You can do a report here:
http://www.tvfool.com/index.php?opti...pper&Itemid=29

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2019-05-25 at 07:57 PM.
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post #8 of 13 (permalink) Old 2019-05-25, 05:38 PM
 
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"Thanks for the input. I understand the points made about line-of-sight, reflections and multi-pathing. But it's still not clear to me how lowering a blind or closing a door on the second floor of our house interferes with the otherwise successful reception of signal by the antenna two floors down."

Well get over it. You asked for advice and you are getting it from the best!!!
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post #9 of 13 (permalink) Old 2019-05-25, 06:02 PM Thread Starter
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Quote:
Originally Posted by ExDilbert
... A common phenomena occurs when someone adjusts an indoor antenna for best signal and then steps away from the antenna and the signal disappears. That's because the person formed part of the antenna whil standing close to it. ...
Thanks, ExD. I've experienced this and I completely understand how proximity to an antenna could cause interference. It's interference two floors away that baffles me. The blind and the door contain no metal. So maybe it is just a complete fluke that a small movement upstairs messes up reception to a basement-mounted antenna that otherwise has no problem getting signal.

Quote:
Originally Posted by Jorgek
... Well get over it. You asked for advice and you are getting it from the best!!!
Get over it yourself. I didn't ask for advice - I asked for some insight into the bizarre reception issues I was experiencing. I got some insight, thanked those who provided it and confessed that I was still unclear on what was happening.

Well, this thread's a wrap for me. Thanks to all who provided actual input. Much appreciated.
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post #10 of 13 (permalink) Old 2019-05-25, 06:16 PM
 
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Quote:
bizarre reception
It's not "bizarre reception". You chose the worst possible place in the home to locate an antenna (short of a Faraday cage) and then get miffed you have crappy reception at times because of the location of your antenna, but rather than fix your poor choice of location you just want to know WHY your reception is crap, hint, it's your stupidity in antenna placement.

201 transmitters

Last edited by Zank Frappa; 2019-05-25 at 11:19 PM.
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post #11 of 13 (permalink) Old 2019-05-25, 07:30 PM
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It was incredible and yet this took place before my eyes, I was connected with it.

Ce n'était pas croyable et pourtant, ceci se déroulait devant moi, j'y étais relié.
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Last edited by rabbit73; 2019-05-25 at 10:16 PM.
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post #12 of 13 (permalink) Old 2019-05-25, 07:31 PM
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I connected my cable TV coaxial cable to a 30 dB attenuator, and now the cable STB doesn't receive anything, and I had to use LTE to get on the internet. Bizarre... I think I will remove the attenuation.


Seriously, if you truly understand the principles of line of sight, multipath, etc. Please put your antenna in that line of sight and get rid of the reflections. Best way to do that is as stated, to get it outside as high as practical, in as close to 'free space' as possible and your reception will certainly improve. My antennas are on the chimney for example.
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post #13 of 13 (permalink) Old 2019-05-26, 02:54 PM
 
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I'd call Rogers first majortom, get a professional to look at it then completely ignore them.

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