Analog vs Digital TV during snowstorms.

It also happens during thunder/rainstorms, then the distortion seems even worse ! ;) I made a video of it back then... maybe I put it on youtube for the fun of it ! or maybe not ;) Video quality isn't that great of my "camcorder" ;)

Bye, Skybuck.

Analog TV utilizes a huge amount of bandwidth, so if some of the signal is distorted, there's still remains enough information to build a recognizable image.

However in digital TV the signal is highly compressed, i.e. the bandwidth of required for a single program greatly reduced. To get an impression: In digital TV one can transmit up to 8 programs within the channel required for one analog program required.

This makes digital TV signals more prone to damage. But it also strongly depends on the used modulation. There are various methods, each with it's pros and cons.

Well, there is forward error correction to some degree, but at some point there's just too many information lost. Google up "Shannon Limit".

Wolfgang

Good quality analog reception requires 40-50 dB of signal to noise ratio (SNR). When the SNR drops by 10-20 dB, the picture is still viewable, although a little snowy. Dropping by 30-45 dB, the frame and line synchronization is finally lost.

Digital signals typically operate at 5-20 dB SNR at _normal_ conditions. If the signal level drops by 10-20 dB, this is below the threshold level and no usable information can be extracted.

It appears that both in the US as well as Europe, the digital proponents of digital-TV did not realize that in normal weather conditions, the signal level could fluctuate by 10-20 dB.

In a line of sight communication system, the received signal strength can be calculated quite accurately and on the TV-satellite to balcony dish path, signal strength can be calculated within 1-2 dB (although heavy rain will cause more loss).

However in terrestrial TV, the normal condition signal levels can be quite different in adjacent places, but also the variability of the signal strength is much larger.

My digital TV works fine, rain, shine, snow, wind. Just don't let anything get inside that little coaxial connector coming from the pole out by the road and everything works just fine.

or

I live at the edge of digital TV reception. One thing that would be really nice is if they put a little more redundancy into the audio channel. I can handle losing the picture.. but when the audio cuts in and out.... I turn the TV off.

George H.

In the US it often has nothing to do with SNR. Our digital channels are nearly all >50dB yet collapse a lot. It seems that multipath throws our DTV off the rocker really fast. In analog we saw slight ghosting when clouds rolled in, in digital it pixelates, turns into a blocky Picasso, freezes and that's it. The spectrum analysis shows no noticeable changes in signal strengths.

In other words... DTV is not really ready for prime-time... wonder who "designed" it ?:-) ...Jim Thompson

Jim Thompson wrote in news: snipped-for-privacy@4ax.com:

a COMMITTEE. ;-)

Sure feels like it. OTOH we have now found a secondary channel with tons of good old movies, on terrestrial 58-2 in our neck of the woods:

Surprisingly this one pixelates out less often so most movies make it through to the end. Of course now we tape everything, it's the only way with DTV because you don't want to watch a movie that freezes into a Picasso 20 minutes before the end.

ThisTV has the potential to make up for the technological grief the DTV switch has cause, even if only one out of two movies made it through.

Jim Yanik wrote:

...made up of people who get their TV via cable.

I have cable but bought a supposedly good powered HD antenna.

1. Wanted backup for when storm knocks out cable.
2. Access to those secondary channels X.2, X.3 etc.

Even LOCAL transmitters don't come in without the antenna up on a mast. Transmitters only 3 miles away!

My impression is that rabbit ears, even ones MADE for HD won't work at all now.

I went to an FCC web site and found that there is apparently a big problem with lack of reception and one explanation says that the HDTV system is more line of sight than the old VHF was.

Trees and terrain screw it up and it's very directional.

A guy from a TV station told me that the new channels use frequencies comparable to the old UHF.

In a few months when the freezing winter weather is gone I intend to try a mast.

Indeed it seems that the FCC really SCREWED UP this television changeover!

I noticed that there are some lobbying groups trying to stop some moves to eliminate free over the air television as well.

Was this crappy transmission system part of some kind of plan to eliminate free broadcast TV?

From the standpoint of disaster preparedness this new Over The Air TV transmission system looks really BAD.

This situation has got to be good for the cable TV outfits!

..the very same dictators that are printing money by the trillions...

One issue is that the amount of information passed through the channel has been hugely increased. Not just a HD signal, but typically a SD channel of the same program and an additional SD channel.

This is possible - but at an inevitable reduction in noise immunity (someone's already mentioned Shannon). If just one SD channel were being transmitted, and the bit rate set accordingly, I dare say you'd see a much better handling of poor tramission conditions.

Sylvia.

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the sad fact is that our police and fire two way radios are also going from analog to digital so when the signal gets a litte weak, instead of hearing a little static along with an important call..., they hear nothing...

the solution then being $old is to erect more tran$mi$$ion tower$..

analog does have some advantages..

Mark

... or want people to have to subscribe?

Not really, at least not in multipath situations and that seems to be a _huge_ weakness of ATSC. When SD channels run on empty without programming it doesn't get better.

If they really want reliability at low cost they should go back to CW! :-)

In the UK, we are transitioning from analogue to digital TV. Currently most areas have both, to give oldsters time to install new tech etc. In a while they will turn off the analogue signal. From a radio program discussion of the problem, I understand the plan is to boost the digital TV signal by several dB once all the analogue signals are gone - but right now, the digital signal would interfere with the analogue one if it was transmitted at full power.

Since the signal should be narrowband, I'm not sure I believe the above, but that's what I heard.

However, as I get older I find TV programs less tolerable and my viewing hours have crashed, so poor reception doesn't worry me much! Now if I was having problems with my broadband...

Same here! I watch O'Reilly and Greta on Fox, amusing quiz shows like "Smarter Than a Fifth Grader" and "1 vs 100" in between, then Leno and the news, "Monk" and old movies otherwise ;-)

Just over the radio... Toyota dealers in Phoenix are offering free hair cuts for men, hair and nail salons for women, and massages for all while you wait on your recall work ;-) ...Jim Thompson