DTT reception and rain?

Dr. Nick · 12-09-2010 7:26pm #1

My reception yesterday evening was kak, due to the rain I think, is this normal? The only issues I normally have is with sound syncing.
I know there hasn't been a launch yet so I assume these problems will be ironed out.

channelsurfer2 · 12-09-2010 7:59pm

rain affects my signal by 20 to 30% sometimes with dtt so could be. lip sync should be sorted hopefully

STB · 12-09-2010 8:51pm

What are you using to receive DTT.

I have had no voice sync issues.

jabarrett35 · 12-09-2010 9:20pm

Rain and fog attentuates UHF reception, but if you are receiving your signal from a local transmitter it shouldn't reduce the signal. Other's on the forum will have more expertise on aerials. What transmitter are you receiving DTT from and how far are you from it? Also topography over which the RF travels will effect reception.

lawhec · 12-09-2010 9:55pm

Rain, or any moisture in the air can affect UHF reception (either analogue or digital), the higher the frequency the more the signal can be weakened though its effect isn't normally as pronounced as rain fade on satellite reception, and if you're in the service area with line-of-sight to the transmitter there shouldn't be problems. They might occour if you're receiving distant, fringe signals and heavy showers, snowfalls or dense fog is taking place (I seen analogue UHF RTÉ reception here in Tyrone close to being wiped out from a summer shower that lasted several minutes a few weeks back, reception returned back to normal within a minute of the rain stopping).

If reception doesn't return back to normal soon after a period of heavy rain, it might be the case that water could have got into the coax cable, masthead amp or diplexer, if that is the case direct replacement is the only answer.

channelsurfer2 · 12-09-2010 10:45pm

cairn hill has the lip sinc issue been a few posts about it. seems to affect live programmes more than others but still has it.

13-09-2010 9:18am

Funilly enough,Rain makes kippure dtt reception stronger in south wicklow.

This is also the case for kippure VHF.

I'm told that VHF reception from wales in the 70's also got stronger with rain and was worse on fair to good days.

As for other uhf dtt-presely here might drop 10% in prolonged irish sea covering rain but it's fog that really gets it.Fog can drop it by as much as 50%
If your signal is generally very strong,this should not be an issue.
I've only ever had momentary 20 to 60 secs max presely drop outs in fog for example and they are so very very rare.Amazing really.

watty · 13-09-2010 10:02am

Middle of graph is 10GHz. Left edge is 1000MHz. Right edge is 100GHz

It's usually collected rain water on the aerial elements changing the aerial tuning or losses. Not the rain in Atmosphere at 470MHz to 860MHz. Hence higher gain aerials are more affected than lower gain and effect can be marginal, better or worse depending on design of aerial, condition of it and vertical or horizontal polarised.

Polishing it / anodised and varnish helps. Never varnish fresh aluminium. It must be anodised or else deliberately oxidized (wipe with salt water and vinegar an hour apart, wash and leave wet to dry.).

WD40 isn't a lubricant or easing fluid for seized bolts. It's actually designed as a long lasting water repellent, so it works well for quite a long while.

Make sure the Aluminium has not got flaky white fluff (uneven Aluminium oxide etc) that holds water. If so sand it down, and either get it anodized or deliberately quickly oxidize it and then WD40 or varnish (only polyurethane). Never varnish straight after sanding/polish as any pinholes will develop huge nasty flakes of oxide.

Tom Slick · 13-09-2010 11:57am

What about deposits left by chimney smoke? Do these have any effect (not just in rain) ?

watty · 13-09-2010 12:55pm

I don't know

lucernarian · 13-09-2010 2:34pm

Thanks for that graph Watty. I can receive TV from Mt. Leinster, Cairn Hill as well as Brougher Mtn, Divis and Kilkeel (more weakly and Kilkeel when Mt. Leinster isn't spewing out DTT on all 4 channels). Rain never made any difference one way or another for me. And yes the aerial is mounted outside:D

I know WD40 is Water-Dispersing, but it is good for seized bolts even if it's not designed for it!

Soot is probably a poor electrical conductor but it depends as each soot contains lots of different substances. The carbon in soot would be an ok conductor, so it may make a small difference if the whole aerial was blackened. I wouldn't know for sure anyway.

Sam Russell · 13-09-2010 3:16pm

To_be_confirmed wrote: »

Soot is probably a poor electrical conductor but it depends as each soot contains lots of different substances.

As you know, aerial design and radio propagation is a black art.:D

watty · 13-09-2010 3:28pm

/me hides book of incantations and robe under fake flagstone.

http://www.dxzone.com/catalog/Software/Antenna_analysis/
(look for NEC, various free programs for Windows to analyse Aerials and Yagi)

http://www.microwaves101.com/

http://www.rfcafe.com/

DTT reception and rain?

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