TV interference

[damia-b]

During the recent cold spell, the interference in TV has been terrible. Digital was virtually unwatchable and on analog there4 were irregular periods with bars of dots across the screen. I noticed that these periods occured about 8 times per hour during the day and more often during the rush hour, so I started train-watching. Whenever there was interference. I could see the bright blue flash from the overhead pick-up as a train passed on the line anout 1000 metres from the house in the direction that the aerial is pointing.

Is is feasible that electric trains cause such interference? The large sparks only appear when there is frost on the overhead conductors so that would be why I have not noticed it before. Any ideas what can be done to remove it? I don't think asking the rail company to fit suppressors to their trains is a starter.

 

[plugwash]

Making sure your aerial is correctly pointed would be my first step. Especially look into what elevation it should be pointed at (that is how far from the horizontal it should be) so that it is pointing straight at the transmitter. A higher gain aerial may alsp help but ONLY if it is pointed corrected.

You can also get "TV interference" filters, they can't do anything about noise that is in-band but some noise may be out of band and yet still having an impact on the TV equipment.

Another option is to give up on terrestrial and go with sattelite. Sattellite dishes are pointed at a very high elevation so they shouldn't be affected much by the noise from trains. This gets pretty expensive if you have lots of TVs though, figure about £10-£20 per port required (remember twin tuner boxes need TWO ports) for the dish+LNB(+multiswitch if needed) plus the price of cable (about £30 a reel) plus the price of whatever boxes you choose (from about £50 for the most basic boxes to over £200 for some high end recorder boxes). Plus installation if you don't fancy doing it yourself. There is also the issue that not all channels on freeview are on freesat.

 

[ChrisFrost]

Try a Log Periodic aerial


Most of the aerials I see around are those huge sails sold as wideband high gain aerials ready for the digital switch over. They look like an accident in a metal bending factory

Log Periodics are better at rejecting electrical interference (impulse noise)

 

[ericmark]

The weather conditions have been unusual and likely you have had a number of factors all effecting the interference.

Isotropic propagation (CB's called it skip) is caused when cold and hot air meet. If this is above the height of the TV mast then it will mean signals travel further but if below then it reduces the signal strength.

 

[damia-b]

Thanks all. Another option that a friend (locally) has mentioned is to turn the aerial about 120 degrees to receive the local station. That way it will not be pointing at the railway. The only thing against that is that it is a relay station and does not carry all the channels that Darvel and Blackhill carry.

Weather is certainly a factor, as two channels have been barely watchable on analog and blank on digital. At the local station gives a good signal on four channels.

 

[ericmark]

It is worth looking to see what has changed. Where I live on a hill near the North Wales / English boarder we also had a problem with local transmitter in that we did not really want to watch in Welsh.
So we have always had the aerial pointing to Winter Hill. However there is now a new transmitter vertical instead of horizontal on the Wirral with both Welsh and English at a single transmitter so slimming so I can get of of window onto the kitchen roof to re-position the aerial.
However since we also have Freesat and Sky+ and internet there is no hurry as far as I am concerned.
You are lucky having analogue been turned off here so my DVD recorder is no longer keep up-dated with time signal. However once turned off the Freeview power is increased so things could change where you are.

 

[FDJ]

Isotropic propagation (CB's called it skip) i.

Isotropic: "invariant with respect to direction". Do you mean "Ionospheric" ?

 

[FDJ]

Try a Log Periodic aerial
Log Periodics are better at rejecting electrical interference (impulse noise)

Only by virtue that their radiation pattern is relatively free from minor lobes.
If the interferance is comming from the direction of the main lobe, the log will not be any different than any other type of aerial.

Frank

 

[Mickymoody]

The weather conditions have been unusual and likely you have had a number of factors all effecting the interference.

Isotropic propagation (CB's called it skip) is caused when cold and hot air meet. If this is above the height of the TV mast then it will mean signals travel further but if below then it reduces the signal strength.

That's correct. Displacing your aerial would bring better results. Maybe 180 degrees out? ie pointing it the wrong way? Or pointing it towards a large building/mountain nearby? As sometimes over modulation, floods the system.

 

[damia-b]

Thanks for all the advice. Reception has been OK for most of the last few weeks, but the return of the frost on Thursday brought a return of the problem. There was a further weird effect. The digital receiver kept jumping out of channel 1 (BBC1 Scotland) to channel 22 (CBBs)!

The display on the box was still BBC1 Scotland, but the programme on the screen was definately CBBs. I do know the difference between Jackie Bird and an animated character. When I switched to the system status display, the signal strength (usually about 75%) was dropping to below 50% and the quality(usually 100%) was also falling to lower levels.

I am considering tilting the aerial up slightly (about 5 degrees) to reduce the interference signal as the railway line is a little below a horizontal line from the aerial.

 

[Mickymoody]

Definate propogation effects, usually in cold/frosty weather, obviously. Maybe rather than focus on the aerial itself, the cable has got a tear in it, and water has got into the braiding, is then freezing, etc, causing a bad picture? I've repaired loads of TV's where the tuner is literally flooded, due to a split wire. And nothing wrong with the aerial at all.

Or are you in an area where terrestrial TV is still running parallel to digital transmissions? If thats the case then the digital transmission isn't running at full strength yet, so maybe nothing wrong, but bad reception due to the crossover? Have you spoken with neighbours that may have had similar issues? When I've setup TV's with internal digital receivers, always had bad results, picking up Welsh channels, or channels missing. What a farce this digital TV switchover is! And Sky is no better. Have a bit of rain. No picture! Great! At least in analogue age, you got a picture albeit snowy, or the case of sky, black/white sparkles (remember those?!). What a step back in technology.