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Totally off topic - why does snow/sleet break up my tv recep

 
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ElizabethD
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PostPosted: Wed Jan 26, 2011 9:26 pm    Post subject: Totally off topic - why does snow/sleet break up my tv recep Reply with quote

Joining Vicky's OT thread a bit below this:
Off the air. Cheap. Hate Comcast. Snow, blizzard, wind, sleet, drizzle, as we speak. Why is the digital TV signal breaking up every few seconds today? Even audio drops out, though not as often as video, while I'm trying to learn about how small can transistors get (PBS) and their cool use.
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vickyg2003
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PostPosted: Wed Jan 26, 2011 10:44 pm    Post subject: Re: Totally off topic - why does snow/sleet break up my tv r Reply with quote

ElizabethD wrote:
Joining Vicky's OT thread a bit below this:
Off the air. Cheap. Hate Comcast. Snow, blizzard, wind, sleet, drizzle, as we speak. Why is the digital TV signal breaking up every few seconds today? Even audio drops out, though not as often as video, while I'm trying to learn about how small can transistors get (PBS) and their cool use.


I have this every time the wind blows. Any time its windy I have huge amounts of pixelation.

Or it could be the weather where the signal is originating.
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jimdunn



Joined: 29 Jun 2004
Posts: 544
Location: NSW, Australia

PostPosted: Thu Jan 27, 2011 12:43 am    Post subject: Reply with quote

With satellite, you can be affected by Rain Fade.
That certainly can and does kill my satellite reception completely in heavy rain/storms - happens about every couple of weeks here.
I'm not sure if or how much Terrestrial DTV can suffer from that - it's not been a problem for me at all here - (but we don't watch much DTV so I'm not a great sample...)
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zaphod7501



Joined: 02 Aug 2004
Posts: 529
Location: Peoria Illinois

PostPosted: Thu Jan 27, 2011 9:21 am    Post subject: Reply with quote

OTA reception is just as affected by weather as analog broadcast was. Its just that it is perfect until it hits a threshold, then messes up.

Since many stations are broadcasting at lower power levels, or have not gone full power, they can be harder to pick up than their old analog counterparts.

Connectors and connections can be affected by moisture and movement too.

PBS offers other problems, often due to very low bit rates that can pixelate even when reception is OK.
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kevjs1982



Joined: 05 Apr 2008
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Location: East Midlands, UK

PostPosted: Thu Jan 27, 2011 4:13 pm    Post subject: Reply with quote

jimdunn wrote:
With satellite, you can be affected by Rain Fade.
That certainly can and does kill my satellite reception completely in heavy rain/storms - happens about every couple of weeks here.
I'm not sure if or how much Terrestrial DTV can suffer from that - it's not been a problem for me at all here - (but we don't watch much DTV so I'm not a great sample...)


In the USA they use ATSC compared with the European and Australian DVB-T format.

The former is supposedly better for covering huge distances, but the latter is more robust (especially in the 8k mode that the UK are adapting as analogue is switched off and I believe most other countries have used from the start) - IIRC the limit for DVB is about 70km, but it's not uncommon for viewers in the USA to be over 100km from their transmitter.

One of the reasons for the huge distances in the states is down to geography, and the other is down to the way TV stations are local with some national content, where as Europe and Aus tend to be national services with some local opt outs making the reception of distant services more attractive in the States. Furthermore in the USA each broadcaster tends to have there own transmitter mast requiring the use of omni-directional antennas which also pick up interference from all directions.

In Europe the scene is much different - in countries where omni-directional antennas are the norm (i.e. Netherlands) the network has been designed to received indoors on portable sets and all the services are broadcast from all the masts in a SFN (i.e. reception from three transmitters on the same frequency actually improves reception); in countries where roof mounted antennas are the norm (UK, France, Germany, Spain) all the broadcasts you can expect to receive are broadcast from a single transmitter mast meaning you only need a single antenna (in countries where VHF is still used this may come from a second mast but would require a second aerial anyway) to receive all the services.

Both the UK and France have six multiplexes* and the majority of transmitters will carry all six multiplexes. About 10% of the population will get only three multiplexes (which carry the main services) but some of those may be able to get the other three with a second aerial but are likely to suffer reception problems (as the reason they have a more local mast is due to a poor/weak signal).

There are exceptions to the rules though - in some areas there are more multiplexes which correct the region available to you - e.g. parts of north east Wales get services from England, but also get three more multiplexes which carry the Welsh services but these come from the same mast as the English ones. Some areas like Derby in the East Midlands get there services from outside there area (i.e. the West Midlands) but have a second transmitter between the city and the mast carrying the wrong region which "corrects" there region for them (i.e. one aerial will pick up the local Derby transmitter with East Midlands programmes, and also the more distant Sutton Coldfield transmitter which carries the rest).

Some areas also get "local tv" stations (a new concept in the UK) but these (well there is only one on air, Channel M in Manchester) come from the same mast that everyone will be using for their main services.

Countries like the UK and France also rely very heavily on over the air television to provide services to the viewers so it is worth the investment in providing a more robust and easy to use transmitter network (the Dutch network was designed specifically for second tv sets and being used on houseboats hence the large number of transmitters operating in an SFN) - in countries like the USA where cable penetration is very high it's not worth providing blanket digital terrestrial coverage when most people won't even use it.

At the moment I have receive a low power digital signal which is co-channel with a more distance transmitter on the same baring on three frequencies so is prone to interference depending on the weather - however from August when our transmitter goes high power these problems are likely to become a thing of the past (although annoyingly one of the multiplex will remain low power in the less robust transmission mode for another two months so as not to wreck a neighbouring regions low power digital signal).

My parents who have gone though DSO (Digital Switch Over) have a robust signal which is never effected by interference unlike the old analogue services were (but then again digital is running at 100kW from a transmitter 17km away, compared with the 12.5kW that the weakest analogue channel used to be at *** analogue was 500kW for the main four stations so the kW power has effectively doubled with DSO.


* One Multiplex uses a single broadcast channel and can carry about 11 SD MPEG2 TV services or 4 HD MPEG4 HDTV services or a number of radio and data services (or a combination of).
** from some point between 2005 and 2015 depending on which country and where in that country you leave - for me it's from this August, although my local transmitter has been carrying all six at low power since 1998
*** remembering that DVB-T digital needs around 10% of the analogue power to match coverage i.e. 100kW DVB-T ~= 1000kW PAL

Oh, and finally getting back to the original question - over Christmas the digital tuner in my parents TV was giving flawless reception on BBC ONE HD, yet we had to keep wiping the snow and frost off the satellite dish to get rid of the dreaded "No Satellite Signal is Being Received" message...
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jimdunn



Joined: 29 Jun 2004
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Location: NSW, Australia

PostPosted: Thu Jan 27, 2011 4:26 pm    Post subject: Reply with quote

I'm in Australia, and we tend to adopt UK formats (albeit 10 years later).

Since I come from the UK that can tend to make me a bore when I say "Ah, yes, we did that in England 10 years ago"

Less so now, though, since, having been here 12 years the comparisons, and opportunities, naturally decrease. I am almost native.

Nevertheless, thanks for the fascinating, detailed answer - much stuff in there I didn't know...

As an aside, for no doubt historical reasons, Australia uses a mixture of UHF and VHF for TV transmission, and has carried that forward to the DTV era, so when, a couple of nights ago, our local transmitter stopped sending UHF due to a fault, we only got half the analog channels, and half the digital bouquet, and the Station owners corresponded - so if you couldn't get Channel 9 analog, you couldn't get it digital either.

Such is progress.
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kevjs1982



Joined: 05 Apr 2008
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Location: East Midlands, UK

PostPosted: Thu Jan 27, 2011 4:40 pm    Post subject: Reply with quote

jimdunn wrote:
I'm in Australia, and we tend to adopt UK formats (albeit 10 years later).


Although Aus did have HD on digital terrestrial for years before we did - it only launched in the UK at the tail end of 2009 (although we do use the more efficient MPEG4 on DVB-T2 with Dolby Digital + - first country in the world with that combo) - alas I have to wait until late August, by which time most of the first F1 season in HD will be over.... Confused
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jimdunn



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PostPosted: Thu Jan 27, 2011 4:50 pm    Post subject: Reply with quote

kevjs1982 wrote:
jimdunn wrote:
I'm in Australia, and we tend to adopt UK formats (albeit 10 years later).

Although Aus did have HD on digital terrestrial for years before we did - it only launched in the UK at the tail end of 2009

You got me there - you are correct.

No content really worth receiving though, hence no take up of STBs, and utter lack of local interest. Until very recently the major broadcasters just had test channels on HD - slowly that is changing.

Even the new satellite HD services here are limited to a few channels.
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ElizabethD
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PostPosted: Fri Jan 28, 2011 8:58 pm    Post subject: Reply with quote

Thanks all for such interesting information and the links. Great stuff.
It did take me by surprise - wind, rain, snow. But now it makes sense.

I'd take the old analog anytime. A bit of snow on the tube every once in a while, but never a totally lost signal.
Oh, the joys of the new, improved Evil or Very Mad , technology

BTW, I use inside-the-house RS antennas and they work fine most of the time (one local channel doesn't come through but I don't care, so long as I get my PBS). I also have a splitter, so I can split it out to watch a cheap comcast service for which I still pay. It's just that their 5-sec delay and mangled, and constantly changing, channel numbers and not updating time on my dvr is why I hate them so.
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jimdunn



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PostPosted: Fri Jan 28, 2011 9:19 pm    Post subject: Reply with quote

ElizabethD wrote:

BTW, I use inside-the-house RS antennas and they work fine most of the time (one local channel doesn't come through but I don't care, so long as I get my PBS).


We have one good indoor antenna, in our daughter's room, and, whilst it works ok most of the time, it will occasionally drop out if signals degrade. You can often fiddle around a little bit with its orientation or internal signal amplifier knob to get the signal back if this happens (very reminiscent of "the old days" - moving antennas around to get a picture...). I don't think I'd tolerate it if she used it much, but she doesn't - she uses her bedroom screen for PC, DVD and Satellite, so I've not bothered running a feed from the rooftop TV antenna to her room, since we had the indoor antenna "lying around". Our other TVs are connected to the rooftop antenna - and as I said above, I've never seen DTV drop out on these, and reception is pretty much perfect - but, again, we're not big DTV watchers - usually we'd be watching satellite or DVD disks/HDD saved content.
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greenough1



Joined: 30 Jan 2005
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PostPosted: Sat Jan 29, 2011 12:11 pm    Post subject: Reply with quote

This is why you want to have the highest possible gain you can so that the threshold for pixelation is never reached by having adverse atmospheric conditions.
I put the biggest highest gain (directional YAGI) antenna I could up on the roof, as high up as I could, along with a pre-amp and I never had issues when receiving an OTA signal from 40+ miles and no direct line of sight. Of course that was UHF which tends to huge the surface of the earth.
In the San Francisco bay area, many stations have switched back to VHF from UHF and OTA reception has been degraded for us far out in the "sticks". VHF is less forgiving of topography.

Best,
jeff
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jimdunn



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PostPosted: Sat Jan 29, 2011 1:53 pm    Post subject: Reply with quote

Indeed.

I've messed around with internal antennas on and off for many years, even once, back 25 years ago, when I lived in a London bedsitter, mounting a proper (although cheap) external antenna inside, in the space above a "kitchen" cupboard, because it was the only option... Confused

Occasionally, circumstances have been sufficient to give a passable reception from inside, from that internally mounted monstrosity, or from the various increasingly clever, smaller, more acceptable looking, internal antenna products I've owned over the years - but never without ghosting or other issues in some conditions.

Never, though, have I had real problems with a properly cabled, suitable rooftop antenna -
(except, of course, for my current bone idleness with not running the last feed from the roof I really need - but we've only lived here 12 months, that's how it was when we bought the place, and we may need to move again next year, so, given the lack of use for OTA in that room, laziness currently trumps perfection...)
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underquark
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PostPosted: Sat Jan 29, 2011 6:26 pm    Post subject: Reply with quote

Wind can blow an external antenna about. Snow, rain, ice build up on the surface of your roof/wall and that is why the internal antennae get affected?

I have two internal antennae - one goes through a splitter/amplifier to supply most of the house and another (which is huge) goes direct to my PVR. I also have a UPS (uninterruptable power supply) on the PVR so this way if there's a brief power failure (not uncommon where I live) I don't lose any recordings.

Incidentally, I can see a 1/2-megawatt transmitter from my house and used to be able to pick up audio through unpowered headphones and certain digital channels without an antenna (just a short length of coaxial cable hanging in there). The digital signals are now transmtited at just 20K but some people report the signal is now too strong in areas where they have switched off analogue and upped the power to digital.
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kevjs1982



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Location: East Midlands, UK

PostPosted: Thu Feb 03, 2011 3:55 pm    Post subject: Reply with quote

greenough1 wrote:
This is why you want to have the highest possible gain you can so that the threshold for pixelation is never reached by having adverse atmospheric conditions.


High gain antennas can be problematic though - especially here in Nottingham where the two local transmitters both have channels which are co-channel with more distance transmitters, the slightest bit of lift and you lose the local services, switching to a rubbish indoor aerial and it's okay!
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