Puzzle

[Screwi]

This sounds to me still like a bad case of RFI - radio frequency Interference.

This can be caused by a local CB'er using an illegal amplifier called a "burner" which pushes their transmission power way beyond legal levels.

It could be a Radio Ham - although these guys generally know what their doing and dont tend to cause problems.

It could be a local taxi firm.

It could be a local taxi rank or private hire taxi local parking spot using illegal AM radio transmitters - AM on around the 27MHz transmission frequency causes havock with tv's and hi-fis etc etc.

Check for the above,

CB'ers will have large arials on the roof or on a mast at the back of the house.

Hams will have beam like arials.

Taxis will be marked LOL and will generally have TWO or THREE ariels - one for the FM radio, one for the cab office - and if theres another ONE for their own radio to talk to there buddies in the other cabs whilst they dont have fairs.

A few pointer sfor you to check.

The DTI - department of trade and industry, or the RCA - radio communications Agency, can be called out to your property in severe suspected cases and they can do some investigation work

 

[HDRW]

I've just noticed that the picture on my PC monitor is unusually dark too. I'm not sure if this is related, but even with the brightness and contrast set to maximum, images still appear dark. Very strange.

Indeed! I think I'd measure the mains voltage at least, but not unless you are sure what you're doing, can do it safely, and have a decent meter to do so.

Oddly enough, I tried plugging a desk lamp into the same double socket as the TV last night, and managed to watch the whole length of a film and still the picture didn't go blue causing the TV to shut down.

This is Sod's Law applied to intermittent faults - they never happen when you're looking!

The UPS sounds like a good idea too. I'll have a look on kelkoo to see how much they are.

Decent ones aren't cheap (APC Smart-UPS for example), and you need one that has a serial link to the PC and periodically reports things like the mains voltage, and events like sags, surges and spikes when they occur. The cheaper ones don't do this, just provide battery backup without telling you what happened.

Cheers,

Howard

 

[supersparks]

ive got a belkin, got it from staples, about £80 and it gives data.

i can't remember the model number

 

[Big_Spark]

The fact that the other TV seemed to work fine upstairs, but not when plugged into the socket downstairs should be a concern. Whilst all the symptoms descibed sound like EMI/RFI, it could also be a fault in the installation.

If it was purely EMI/RFI from the local area, then it would have the same effect upstairs or downstairs, the fact that this is not the case, wwhilst not ruling it our completely, makes it unlikely.


I know you got an Electrician in , but was he a mate or did he really know his stuff? I ask as there could be a fault in the MCB feeding that circuit, although this is more likely if the circuit has an RCD/RCBO protecting this circuit.

The other possibility is a neutral fault of some description, transient neutral faults can be a bugger to track down, but for certain equipment they are a real pain in the proverbial.

 

[andyb32]

The portable TV has not been working upstairs because I need to get a power socket installed in the wall in my bedroom. I also need an aerial socket to be fitted.

As far as I know, this problem is affecting the whole house (in light of the issue with the computer screen). The voltage being supplied to the house has been checked and found to be 242 volts. This should not in itself cause a problem, since I understand the appliances generally are tolerant between 220 - 250 volts.

Still non the wiser, I'm afraid.


Andy.

 

[andyb32]

At last! I may have figured out what has been causing the electrical problems at home...

It looks as though the electrical problems I've been experiencing are due interference from the mobile phone mast. Apparently, mobile phone masts transmit from the bottom of "Group A" range (approx. 380 - 460mhz) to "Group C" or "Group D" (approx. 486mhz). This is the information an aerial fitter gave to me.

I recently needed to replace my old TV aerial. The new one has a wider frequency range than the old one (perhaps the reason why my neighbour doesn't appear to be affected). The new aerial has a range of 470 - 860mhz, which would appear to intersect with the mobile phone transmitter range. Apparently, my aerial is positioned directly in the path of the mobile phone mast.

Just to be absolutely sure that this is the cause of the electrical problems, I intend to reposition my aerial such that the gable end of my house will shield it against the transmissions from the mobile phone mast. I may also need to fit some filtering equipment to my house. If this does the trick, I'll be looking to recover some of the cost from the mobile phone organisation responsible (?) for erecting the mast / the local council. Perhaps the council should be my first port of call? Does anyone have experience of this sort of thing happening?


Andy.

 

[mapj1]

I don't really beleive that explanation- to have a problem, the filtering in the tuner front end of your telly would have to be weasel-pee poor.
If true, then legally such, you are receiveing legitimate transmissions for which your equipment is inadequately immune. Unless you can show that the mobile phone company equipmnet is broadcasting a spurious signal within the broadcast band, and the neighbours not seeing it makes that most unlikely, it would be your receiveing equipment that is at fault. The cell operators may make a good will gesture, but are not obliged to do so.

Consider fitting a bandpass filter in the antenna cable to your telly to prove/disprove the theory. Much cheaper than a new antenna, although most aerial installers seem not to have heard of them. (anti 'tetra' filters are often bandpass..)
Sorry to rain on the parade.
M.
PS you don't have one of these dreadful wide as a barn door 'universal aerial booster' type amplifers stuck in the loft or anything do you? These often have much poorer immunity to interference than the TV itself (there is a full product standard for TVs, not so for the £9.99 accessories), and when overloaded these can give all sorts of exciting symptoms.

 

[Careful_Bodger]

Like mapj1 - this does not ring particularly true to me either. The story sounds a bit wonky.

You should note that public use mobile phones don't use these bands - but perhaps your advisor meant the TETRA system - a sort of mobile phone for the police and other services, etc.

See http://www.wibble.co.uk/links/ukspectrum/specbw.html#b400 for (much) more tecchy info on spectrum allocation.

If it were TETRA then the symptom would be more like those described in http://www.wrightsaerials.tv/Tetra.htm

Apologies for not necessarily helping.

 

[andyb32]

Maybe it's the new aerial that is causing the problem. The aerial fitter (a different aerial fitter than the one who installed the new aerial) did recommend fitting an anti-TETRA filter.

I don't have a universal aerial booster, but I am considering fitting a distribution amp in the loft. Is this a bad idea, or are there just particular types I should avoid?


Cheers,

Andy.

 

[mapj1]

The problem with the amplifiers is that they can't know what channel you are watching, whereas the TV has a narrow filter that is retuned to the current channel, the wideband amplifier is just that, and amlifies all signals, wanted and unwanted equally, thus making the interference worse in some cases. Probably the best is to fit an amplifier known to include a filter, or to add filtering externally. I don't have a list of good or bad ones, I'm afraid
Is your aerial fitter open to a try before buy "sale or return" on the filter he suggested?

 

[andyb32]

Yes, I see what you mean. I have recently purchased a freeview digi-box. I wonder if that has any filtering on it? Maybe I should just avoid installing a distribution amp.

Having said that, moving the aerial might do the trick, so that the gable end of the house blocks out the interference (that's the intention, anyway).


Andy.

 

[jtaunton]

If you've got a mobile mast nearby, there should be a ground base-station, which could be anything from portakabin sized down to one of those green boxes that telephone engineers open up from time-to-time, but somewhere nearby you should be able to find a plate giving details of the operator, site number etc. A call to them will give you a go-live date for the equipment and then you will know whether this stacks up with when your equipment started to go wrong.

This is affecting your TV, DVD and Hi-Fi - Are they all linked together ? If not, that may rule out the broadband aerial theory, but not necessarily RFI. This is a very long shot, but there may be something wrong with the base-station installation so that a killer-sidelobe is somehow beaming into your front room and knocking out your equipment but as I said, it is a very long shot.

One final thought which may be worth investigating - A TV aerial looks like it does to make it directional (i.e. mostly receive signals from the direction that it is pointing in). If the aerial has, for some reason, not been connected properly, your co-ax could be sitting unconnected to the aerial and acting as an Omni-Directional aerial (I.e it receives signals from all directions). If you live in a strong TV signal area, then the TV picture would still be perfectly good, but it would also leave you open to the TETRA signal getting in which, as stated elsewhere in this forum, is close to the TV signal part of the spectrum. Try disconnecting the aerial and running it with just one of those portable aerials for a bit. The picture won't be so hot, but you can see how long it will run for....

 

[andyb32]

Wow, a killer-sidelobe beaming into my front room? Sounds a bit like star trek! I'll check out the base station to see if I can get details of the operator & site no. etc.

It seems to be affecting all the equipment in the lounge, which are linked together.

Maybe I should try plugging in a portable aerial too.


Cheers,

Andy.

 

[Scoby_Beasley]

Star Trekkin'. accross the universe, always going forward, never in reverse,
(et al)