What Makes DTV Go Out When It Rains?

[Markxxx]

By digital TV I mean OTA reception.

I can't get TV at my flat, but I have a laptop with a digital tuner. So I'll take it to the library or some other place, if I have to watch TV. This is OK with my silver sensor, but I noticed when it starts to rain, the signal breaks up a lot.

What exactly causes that? That is, if there is an exact cause. Do the rain drops themselves interfere? And this was just a lot of rain, I don't mean lightning.

Also since I only use a Silver Sensor and a tuner for a laptop computer, could this be the issue. Does rain not break up DTV on a real TV with an outdoor antenna?

 

[KeithE4]

By digital TV I mean OTA reception.

I can't get TV at my flat, but I have a laptop with a digital tuner. So I'll take it to the library or some other place, if I have to watch TV. This is OK with my silver sensor, but I noticed when it starts to rain, the signal breaks up a lot.

What exactly causes that? That is, if there is an exact cause. Do the rain drops themselves interfere? And this was just a lot of rain, I don't mean lightning.

Rain causes increased path loss that gets worse with frequency. A severe thunderstorm, such as a monsoon rain in Arizona, will block satellite reception (12 GHz signals from 22,000 miles away) as well as normal OTA reception. Because digital transmission methods are not forgiving of very weak or phase-distorted ("ghosts" in the analog world) signals, they go away. Weak analog signals, especially on UHF, might get more snowy, but digital is either perfect or nothing, with only a small range of pixellation.

Fog could also cause this. Heavy cloud cover could cause reflections that would kill digital reception, while only causing ghosts in the analog world.

Also since I only use a Silver Sensor and a tuner for a laptop computer, could this be the issue. Does rain not break up DTV on a real TV with an outdoor antenna?

Performance is always better with a large, outdoor antenna. The fact that the transmission method changed from analog to digital doesn't change the propagation characteristics of VHF and UHF frequencies. You still need a good antenna, fed with good quality coax (RG-6, not RG-59).

And, a steel-and-concrete building such as a library will attenuate RF signals, which will make matters worse with the limited setup you have.

 

[landtuna]

Performance is always better with a large, outdoor antenna.

I haven't found that to be the case in my personal experience. I have a large combo roof-mounted VHF/UHF on one TV and a $10 indoor loop/ear set top from Walmart on another. The height above ground is almost exactly the same for both yet the set top consistently pulls in 100% DTV whereas the roof antenna is frequently failing in the VHF range.

I used the same roof top antenna during the analog days and had no issues whatever with RF 8 and 10 - the two stations most frequently affected by poor reception. No issues on UHF - even the LP's.

 

[Markxxx]

KeithE4 thanks for the explanation

Anyone else have personal experience with this? If so what?

 

[landtuna]

Also since I only use a Silver Sensor and a tuner for a laptop computer, could this be the issue. Does rain not break up DTV on a real TV with an outdoor antenna?

It is possible your laptop tuner needs a stronger signal than a 'real' TV but it is more likely it is the location of your antenna that is the cause of any DTV breakups.

However.....in the 18 months since the DTV conversion I have found that a multitude of phenomena can cause DTV failure, such as:

Clear blue skies
Wind (with or without dust)
Sunshine from in "back" of the transmitter antenna (summer months)
Sunrise and sunset
Human bodies moving around the receiving antenna (most surprisingly in back of the antenna)
VHF transport frequencies

DTV's only seeming advantage is its picture quality but then only on the primary channel as multiple HD pictures cannot be supported (unless run at less than optimum bitrates) and then only if the receiving TV is capable of very rapid decoding so as to not drop frames.

In short, DTV is, at best, a very fragile technology. It has neither the range nor robustness of analog and it has the "cliff" effect of dropping out completely instead of gradually fading making viewing from a distance or during inclement weather virtually impossible.

IMHO, digital TV, unlike the great number of other digital services, is not a step forward.

P.S. Keith described the electrical wavelength issue of rain interfering with DTV but it also has to do with the transport frequency. Satellite transmitters use a very high (Gigahertz) transport frequency in which the electrical length of a cycle is almost exactly the physical size of a raindrop. This is why rain most seriously attenuates a satellite downlink signal. OTA frequencies are longer in wavelength so rain does not attenuate them nearly as much although it does affect the digital content more than analog. Satellites also operate at much less transmit power than does OTA TV (several hundred watts as opposed to 1MW and more).

 

[ansky212]

I have a Silver Sensor antenna that is designed for indoor use, but I actually have had it sitting outdoors on my roof for the past 2 years. I get much better reception having the antenna outdoors compared to when I had it indoors.

 

[gregg75]

A good wind can take it out also, but usually just enough to be annoying.......and that's mostly
on the low power stations.

 

[vchimpanzee]

I find it's usually fine in rain--this was also true in tha anlaog era in certain situations.

Wind seems to be a problem these days. I only had the problem on one channel during the early months but now it seems to be all of them.

Hot weather is also a problem. I just wonder if this is the same phenomenon that causes people to pick up distant stations. Something has to be causing that interference.

I just mostly watch cable.

 

[Bob1370]

A lot of these problems have the same cause--insufficient signal power. Most DTV signals are transmitted OTA with only a fraction of the ERP analog signals were allowed...and the FCC is beginning to think their predictions about DTV coverage were way too optimistic.

We may soon see two things; 1) A lot of heritage stations pushed back down to their old VHF channel assignments, and current U's pushed down further on the band and closer to each other on first or second adjacent channels (channel adjacency isn't a big issue for digital TV) to clear space on the middle to upper UHF band for broadband operations, and 2) Every station allocated MUCH higher effective radiated power, probably something close to the visual ERP they got in the analog days.

 

[landtuna]

A lot of these problems have the same cause--insufficient signal power. Most DTV signals are transmitted OTA with only a fraction of the ERP analog signals were allowed...and the FCC is beginning to think their predictions about DTV coverage were way too optimistic.

We may soon see two things; 1) A lot of heritage stations pushed back down to their old VHF channel assignments, and current U's pushed down further on the band and closer to each other on first or second adjacent channels (channel adjacency isn't a big issue for digital TV) to clear space on the middle to upper UHF band for broadband operations, and 2) Every station allocated MUCH higher effective radiated power, probably something close to the visual ERP they got in the analog days.

It would have been professional of the FCC to have tested DTV much more thoroughly before cutting everyone over and then finding the shortcomings.

 

[Bob1370]

"It would have been professional of the FCC to have tested DTV much more thoroughly before cutting everyone over and then finding the shortcomings."

Throughout its history, all the way back to 1934, the FCC has been, first and foremost, a group of political appointees most sensitive to the political ramifications of decisions they were making about a growing major industry, rather than professionals schooled in the practical complexities of that industry.

Considering that, it's amazing we ever got a working television system at all...

 

[BMR]

Just to be awkward, my DTV reception actually improves when it rains. ;D ;D

 

[Markxxx]

Well who decided on the power levels for DTV? I mean it shouldn't take a genius to figure this out. I can't but I'm sure engineers know it.

It seems to go back to the early 50s when the allocations for analog were not calculated correctly and you had weird things like channel 7 in New York City, Washington DC and Wilmington, DE. It doesn't take a genius to figure out Wilmington was too close. And then of course a lot of the VHF had to be changed in OH and even in IL and Milwaukee and Michigan.

It seems like they need to get DTV channels all reassigned for maximum potential. Of course not knowing what spectrum will be used isn't gonna help.

<end rant> ;D

 

[KeithE4]

It seems to go back to the early 50s when the allocations for analog were not calculated correctly and you had weird things like channel 7 in New York City, Washington DC and Wilmington, DE. It doesn't take a genius to figure out Wilmington was too close. And then of course a lot of the VHF had to be changed in OH and even in IL and Milwaukee and Michigan.

The Milwaukee/Kalamazoo problem was Channel 3, with WTMJ Milwaukee moving from 3 to 4, forcing WBBM-TV Chicago to change from 4 to 2.

You also had Channel 4 in NYC, Schenectady NY, Lancaster PA, and Washington, with WGAL Lancaster moving to 8 and WRGB Schenectady moving to 6. Same with Channel 6 in Philly and New Haven CT, with WNHC New Haven moving to 8, allowing for the WRGB move.

 

[nocomradio]

I live in what is definitely a fringe area when it comes to OTA TV. The closest station to me is a 45 mile away NBC affiliate. The next are between 50 and 65 miles away. My reception is spotty at best with a DTV antenna mounted on the roof at approximately 40 feet high. I need to install a rotator to really optimize anything I do manage to pull in, but with that setup at those distances, I can pull in about 3 channels now and they will drop out without warning, even on a clear day no matter what I do. Rain, heavy low cloud cover and yes, even wind (I thought I was the only one who had that problem) will cause pixelization, then drop outs.

Go back to the old analog days, and I could easily watch at least 10-12 channels with a rooftop antenna and most very clearly at that. Granted I don't watch much TV at all, but that was a real drop in both quantity and quality for me, nearly overnight. Until these stations ramp up the power, there is little that I can see that could be done to improve things.

 

[vchimpanzee]

Just to be awkward, my DTV reception actually improves when it rains. ;D ;D

That's usually true for me too.

 

[vchimpanzee]

I live in what is definitely a fringe area when it comes to OTA TV. The closest station to me is a 45 mile away NBC affiliate. The next are between 50 and 65 miles away. My reception is spotty at best with a DTV antenna mounted on the roof at approximately 40 feet high. I need to install a rotator to really optimize anything I do manage to pull in, but with that setup at those distances, I can pull in about 3 channels now and they will drop out without warning, even on a clear day no matter what I do. Rain, heavy low cloud cover and yes, even wind (I thought I was the only one who had that problem) will cause pixelization, then drop outs.

Go back to the old analog days, and I could easily watch at least 10-12 channels with a rooftop antenna and most very clearly at that. Granted I don't watch much TV at all, but that was a real drop in both quantity and quality for me, nearly overnight. Until these stations ramp up the power, there is little that I can see that could be done to improve things.

The problem with that is more interference from the stations with the higher power, and then that messes up signals too. For VHF, though, that shouldn't be too much of a problem since no one wants to be there.

 

[flashback]

as i said before as far as over the air television as a whole the nation was better off with analog.

granted some people are getting good reception al the time.granted with the right antenas it is possible to do that .but people shouldn`t have to be doing a lot of reserch to find out what kind of antena will work best.not everyone can figure out what kind of antena to use.

people say just get an outdoor antenna.not everyone can afford that and not everyone is in a position to where they can get an outdoor antena because of apartment living and such.

with analog no matter where i watched non-cable over the air tv , be it at home or at other places the reception was generaly good and there were no dropoffs of the channels.

 

[dave73]

I live in what is definitely a fringe area when it comes to OTA TV. The closest station to me is a 45 mile away NBC affiliate. The next are between 50 and 65 miles away. My reception is spotty at best with a DTV antenna mounted on the roof at approximately 40 feet high. I need to install a rotator to really optimize anything I do manage to pull in, but with that setup at those distances, I can pull in about 3 channels now and they will drop out without warning, even on a clear day no matter what I do. Rain, heavy low cloud cover and yes, even wind (I thought I was the only one who had that problem) will cause pixelization, then drop outs.

Go back to the old analog days, and I could easily watch at least 10-12 channels with a rooftop antenna and most very clearly at that. Granted I don't watch much TV at all, but that was a real drop in both quantity and quality for me, nearly overnight. Until these stations ramp up the power, there is little that I can see that could be done to improve things.

The problem with that is more interference from the stations with the higher power, and then that messes up signals too. For VHF, though, that shouldn't be too much of a problem since no one wants to be there.

It's mainly VHF-Lo that no one wants to be on. There are stations that don't mind being on VHF-Hi, but they need that extra boost in power to get their stations out more. Some VHF's have asked for UHF channels, while others are seeking UHF translators to cover the immediate areas of the markets to reach those who can't get them on VHF.

 

[kenglish]

When the allocations were set, the FCC assumed that people would be obeying the laws. Unfortunately, every piece of consumer electronics junk made since then adds interference, especially on the VHF channels. Don't even get me started on things like light bulbs, and Plasma TV interference .

I have to agree, there should have been more (receive) testing....I wish that the ATSC and FCC had offered converters and other equipment to hams, SWL's, engineers, etc to test the ability to receive the signal under widely varying conditions. Those kinds of tests were beyond the scope of the ATSC or FCC. We needed feedback from hundreds/thousands of viewers.

Also, I fault whoever cut out the budget for the ATSC Test Lab. Just because DTV was "invented now", did not mean the job was "done". Every TV set, converter box, antenna, cable, connector, amplifier,.....ALL should have been tested and certified. Now, we have uselass pieces of junk that don't work, "miracle antennas" that make exorbitant claims, wrong amplifiers for the job, etc. Many sets do not conform to the ATSC standards on things like PSIP. The ATSC Test Lab should have been expanded, not cut.