Effect of weather/atmospheric conditions on OTA TV? - AVS Forum
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post #1 of 16 Old 01-19-2012, 02:06 PM - Thread Starter
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I was wondering what I can expect from a well designed OTA TV system during different weather conditions? The Dish we have now basically works fine except in really driving rains (and I mean coming down in sheets-normal rainfall doesn't phase it), and of course when it gets covered with snow. What kinds of weather and/or atmospheric conditions can affect TV transmissions? Are sunspots, solar flares, and other atmospheric conditions typically a factor? I had a neighbor growing up who was a CB enthusiast who had a 60' tower in his backyard, etc... I remember him talking about something called "the skip" that happened either during a certain time of year (or during certain kinds of weather-I don't really remember), but basically whatever this condition was it allowed the waves to bounce of certain parts of the atmosphere, allowing them to travel much much farther than usual. Is anyone familiar with this phenomenon and does it apply to television waves?
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post #2 of 16 Old 01-19-2012, 02:44 PM
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If you want to install an antenna for OTA channels, it shouldn't be a problem and probably better than satellite (E*/D*) due to inclement weather.

Are you looking to unsubscribe to Dish and just use an antenna or seeking an answer to a hypothectical question about reception issues?

In other words... what exactly is your question/problem/desire/expectation?
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post #3 of 16 Old 01-19-2012, 03:43 PM
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In general weather does not have a huge effect on OTA, but it really depends on how strong the signals ares at your location.

We are in a fringe area so seasons are more important then weather. Our antenna is lower then tree tops so we get worse reception on weak stations during the summer then winter.

If you have not already done so plug you address into TVfool to model expected signal strength.
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post #4 of 16 Old 01-19-2012, 04:11 PM
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Quote:
Originally Posted by Ratman View Post

If you want to install an antenna for OTA channels, it shouldn't be a problem and probably better than satellite (E*/D*) due to inclement weather.

Are you looking to unsubscribe to Dish and just use an antenna or seeking an answer to a hypothectical question about reception issues?

In other words... what exactly is your question/problem/desire/expectation?

My neighbors have Dish and DirecTV. I have a modest outdoor antenna. I can say from my experience:

During very heavy rain they lose signal, I keep mine.
During very heavy snow, they lose signal, I keep mine.
During heavy winds (that move the trees) they keep their signal, I have minor breakups once in a while.
During major tropospheric events, my neighbors keep their signal, and I get to watch TV from out of state markets!

Add in the fact I don't pay for my TV programming, and I say I come out ahead.
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post #5 of 16 Old 01-19-2012, 07:58 PM
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Here is a good read about tropospheric DX modes, which are influenced by weather and by far the most common factors that cause OTA TV signals to occasionally travel farther than they normally would. Other factors, such as "skip" like you mentioned, are driven by ionospheric, solar, or other atmospheric conditions and aren't very common, but can greatly affect OTA TV signals when they do appear. The last skip event I can remember here was in 2008, during which time I was able to tune in a TV station (in analog) from over 1100 miles away with just an indoor antenna.

How frequently you might see the weather-related events occur depends mostly on where you live, with relatively flat, warm, moist (coastal) regions seeing them most frequently. Even so, being that these conditions are not considered normal, distant TV stations brought in by them can quickly come in and go out, meaning you cannot rely on these signals as you would the signals of your closest, local, stations.
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post #6 of 16 Old 01-20-2012, 01:10 PM
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Another problem is lightening. A bolt of lightening will often cause a moment of pixelization. This problem became more widespread after many digital stations moved to VHF after the analog shutoff since it affects VHF more than UHF.

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post #7 of 16 Old 01-20-2012, 03:33 PM
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I've been watching OTA TV since there were all 82 channels (2-83) reserved for TV stations, and DIY hobbies were still popular. The TV frequencies (wavelengths get shorter as frequencies get higher, BTW) ranged from the low VHF band to the high UHF band. Within this range of frequencies are three distinct bands: VHF-LO, VHF-HI and UHF.

Back then, UHF was kind of mystical because most consumer electronics designers had little experience in this band, and equipment quality varied widely. These days the roles are reversed, as UHF is widely used and lower frequencies' peculiarities have made them less desirable. Here's a very basic synopsis of the main qualities of the bands:

VHF-LO: Generally for line-of-sight use only. Long wavelength requires large antenna to work best. Good for long range reception, although TV frequencies were mostly immune from the interactions with the universe that made shortwave bands so much fun. Good point-to-point performance in forested areas. Poor penetration of buildings and other structures. Used to be preferred in LMR (land mobile radio) use for rural areas.

VHF-HI: Mostly for line-of-sight use only. Shorter wavelength more practical for building and vehicle mounting of antennas. Suitable although not ideal for longer range communications. Shorter wavelengths offer fair building penetration, especially at higher powers and/or close range. A compromise of the benefits and problems associated with lower and higher frequencies. Used to be preferred in LMR use for suburban areas. Still the band of choice for aeronautical communications and fire departments.

UHF: Strictly for line-of-sight use only. Even shorter wavelength most practical for hand-held, as well as other antenna mounting. Suitable only for line-of-sight communications. Excellent penetration into buildings, but poor performance in wooded areas. Can be made to perform well in all areas through the use of high mounted "look down" antenna/repeater infrastructure. Preferred in LMR for urban areas. Preferred for ATSC television broadcasting.

Satellite TV also uses different frequency bands in the SHF region and beyond. C Band was and still is used for network TV program distribution. It was used briefly for home reception, but is no longer supported for home use mostly. Every Satellite TV service in the US uses the Ku Band. The Ku Band's shorter wavelengths allows smaller antennas for a given amount of gain and spatial selectivity. (With the Clarke Belt as crowded as it is, it's often more important to be able to focus on one "bird" and reject its neighbors than it is to achieve enough gain and S/N ratio.

While consumer Ku systems are prone to fading with high levels of precipitation, there are many misconceptions about why this happens. Briefly, it's not related to any resonances in of water or its component elements. It's just that water is the most common form of matter to get in the way of a line-of-sight signal. This is exacerbated by the demand for smaller, cheaper and "less ugly" antennas, which must be mounted outside because they can't "see" through walls either.

Electrical discharges such as lightning often do interfere with TV reception of all kinds. This is because most electrical discharges produce the same kind of electromagnetic energy that TV transmission relies on. Needless to say, blotting out the organized signal with a random one will cause a loss of information.

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post #8 of 16 Old 01-20-2012, 04:18 PM
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I'm saddened to hear that UHF is "Strictly for line-of-sight use only" considering how many people I know are receiving UHF channels in their basements.

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post #9 of 16 Old 01-20-2012, 04:46 PM
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Quote:
Originally Posted by scowl View Post

I'm saddened to hear that UHF is "Strictly for line-of-sight use only" considering how many people I know are receiving UHF channels in their basements.

Why is that sad?

The same basic "look down" technology and the shorter UHF wavelengths that make it possible to receive line-of-sight TV broadcasts and cellular service is saving lives of citizens and the public servants who serve them every day. My idea of sad is having someone die while paramedics struggled to establish contact with a physician, or never arrived because nothing happened when the stricken person used the only phone within reach, the cellphone, and couldn't connect.

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post #10 of 16 Old 01-20-2012, 09:05 PM
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Quote:
Originally Posted by scowl View Post

Another problem is lightening. A bolt of lightening will often cause a moment of pixelization. This problem became more widespread after many digital stations moved to VHF after the analog shutoff since it affects VHF more than UHF.

Lightning is a huge problem here for VHF OTA reception. And the lightning doesn't have to be that close, just anywhere in the region. The pixelization can be overlooked - it's the audio dropouts that are so %$&*#@ annoying. Fortunately in our area, we only have one commercial DTV channel that opted to stay on VHF - the rest of them abandoned it for the more reliable UHF band.
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post #11 of 16 Old 01-21-2012, 09:38 AM
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Lightning is bad here in eastern NC on WNCT channel 10, but does not seem to affect WCTI on channel 12. I am not sure if it is because they have a circular polarized antenna, or if it is because their tower is a bit closer to my location? WNCT tower 41 miles out, WCTI 23 miles. The UHF are unaffected.
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post #12 of 16 Old 01-21-2012, 09:50 AM
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Could be location and power. Also, ch 12 being higher frequency than 10, perhaps it is slightly less prone to lightning dropouts (?).
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post #13 of 16 Old 01-21-2012, 11:54 AM
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Quote:
Originally Posted by Badfish740 View Post

I was wondering what I can expect from a well designed OTA TV system during different weather conditions? The Dish we have now basically works fine except in really driving rains (and I mean coming down in sheets-normal rainfall doesn't phase it), and of course when it gets covered with snow. What kinds of weather and/or atmospheric conditions can affect TV transmissions? Are sunspots, solar flares, and other atmospheric conditions typically a factor? I had a neighbor growing up who was a CB enthusiast who had a 60' tower in his backyard, etc... I remember him talking about something called "the skip" that happened either during a certain time of year (or during certain kinds of weather-I don't really remember), but basically whatever this condition was it allowed the waves to bounce of certain parts of the atmosphere, allowing them to travel much much farther than usual. Is anyone familiar with this phenomenon and does it apply to television waves?

It depends, in part, on where you live in relationship to the transmission towers. LOS is very important. In our case, we live about 45-50 miles from the towers but have an unimpeded LOS. High winds, pouring rain, freezing temperatures, fog, summer heat have no effect at all on our reception. However, our antenna is roof mounted, about 30' from ground level secured with 3 sets of guy wires and is a 79 element, UHF-VHF-FM antenna.
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post #14 of 16 Old 01-21-2012, 07:23 PM
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Quote:
Originally Posted by scowl View Post

I'm saddened to hear that UHF is "Strictly for line-of-sight use only" considering how many people I know are receiving UHF channels in their basements.

Or people in a valley with a huge hill directly in front of the antenna, between it and the transmitters 70 miles away. Lots of folks in my area getting UHF that way. UHF is not strictly LOS.
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post #15 of 16 Old 01-22-2012, 04:10 AM - Thread Starter
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Quote:
Originally Posted by arxaw View Post

Or people in a valley with a huge hill directly in front of the antenna, between it and the transmitters 70 miles away. Lots of folks in my area getting UHF that way. UHF is not strictly LOS.

You've actually touched on something that I'm currently wrestling with. I live in a small valley (elevation 400') and three miles to my east is a hill (800' elevation-400' higher than me) that breaks the LOS between me and the NYC transmission towers (about 1200' high) 48 miles away. Many have already told me that NYC reception is either impossible or so poor its not worth it.
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post #16 of 16 Old 01-22-2012, 04:39 AM
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Reception behind a hill is often possible and certainly worth a try. It's usually a trial and error process to find a hot spot for all your channels of interest, much like using an indoor antenna. And the antenna hot spot is often in very unorthodox places. See:
http://www.hdtvexpert.com/?p=134
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