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On Sat, 2013-03-02 at 19:37 +0000, Simon Waters wrote: > Okay totally off topic but I know the crowd here, and you've had several > years now to get experience with Digital TV since I last pondered this one. > > Have been given ultimatum by her who must be obeyed to sort the > interference on the TV. > > This is some sort of impulse interference mostly caused by motorbikes > and lawn mowers, but also a couple of things we can't pin down but > almost certainly something the neighbours do, since we've powered off > everything in the house in a previous troubleshooting effort including > heating, freezers, computers, WiFi, mobiles and the like. Mostly it is > short lived, but can last longer and lead to upset small boy (or woman). > > Two options spring to mind. > > 1) Outsource it e.g. professional Freesat installation. > > 2) Figure out where the signal is picked up and sort it. > > I figured (2) was worth a punt, since it is probably going to be a lot > cheaper, and the nightmare scenario of doing (1) and still getting the > interference has to be considered. > > The aerial and cabling hasn't been touched since the previous owners set > it up for analogue TV. > > Layout is: > > Loft mounted aerial. Not ideal but I don't want to remount it externally > if I can avoid it, and the signal is clearly good enough 99% of the time. > > Passive UHF filter (unshielded). I assume this is a bandpass filter, box > strapped to a rafter just below the aerial, no power, simple circuit > board no shielding at all (well plastic case which is in poor repair). > Doesn't look like a clever design to me, but makes sense given the > presence of an amplifier for it to have been added. > > UHF Booster/UHF splitter. White unlabelled boxes clearly bought as a > set. Suspect this was the previous owner adding TV point in the kitchen > as the install is different quality to the other cabling work which is > all fixed down to rafters. > > Booster had two leads out of it till this afternoon, one was feeding > some wallplates we don't use. Disconnecting the spare lead doesn't > appear to have resolved the issue. > > ~10m cable run to wallplate. > > Wallplate. The wallplate whilst using the simple unshielded connectors > is in a galvanized steel box, and the front plate is also metal > (presumably steel with brass effect finish to match the others). So I'm > guessing it isn't the weak point in the shielding that various websites > suggested it can often be, but hard to be confident. > > Fly lead to Digibox. > > Fly lead and SCART to TV. > > The online advice I've found is nearly all cribbed from the same > original source. It all contains the phrase - "This problem is more > common with loft aerials than rooftop aerials." - which gives away a > common origin. I suspect it was written by a guy selling high quality > co-axial cable as his site recommends buying higher quality co-axial > cable from himself, which may not be a bad idea. > > Questions: > > Anyone experienced similar and sorted it with terrestrial Digital? I'm > wondering if it is pretty much inevitable with the technology in use. > > My guess for weak spots are: > > a) Antenna (being in roof) > b) The Passive UHF filter before the amplifier because it is unshielded. > c) The Digibox itself - cheap one from Tesco on the expectation HD > digiboxes would arrive soon when purchased. It is too light to have much > if any shielding internally and the case is plastic. > d) Cables > > Which would folk address first? > > Is their a diplomatic way to ask to borrow your neighbour's petrol > driven lawn mower for testing? Or a good way of impersonating a noisy > petrol engine. As it is one of the few predictable ways of generating > the interference. > > Has specification of boosters and UHF bandpass filters changes for > Digital TV? > > Should I also be concerned with noisy mains? > > Anything else I should try first? > > The galvanised wallplate has an earthing point on it, but no earth is > attached. I imagine this is not an uncommon state of affairs. I can't > see it should matter, and I don't have a convenient real earth. Is this > a problem? > > > Costings > > Replacement passive filter with shielding is about Â10 and easy to do. > > New satellite quality cable is only slightly more but given the current > cable has no slack, I suspect it will be a pain to thread through, but I > might be wrong on that. > > Digibox I was thinking put it in a metal biscuit tin as and when the > problem occurs. Just have to find a biscuit manufacturer still supplying > proper tins. Would this likely shield it enough if it is the problem? > > Aerial - I think I'd go with Freesat before trying to move this outside > or replace it, since the price difference is going to be negligible. > > We have this in Minions I think the signal for us is too strong ( loft ariel) ((the transmitter is just 1000m away)) so I've turned off the Splitter / booster put an attenuator in the line to each tv and now we only get the occasional blip when a car, lorry runs through Minions. The test would be to have a tv in the loft with a good bit of shielded cable and see what happens! -- ________________________________________________________________________ Regards Kevin Lucas Minions Post Master(Sub) A dedicated Linux user /usr/bin/microsoft Skype minions_shop www.minionsbandb.co.uk www.tearooms.minionsbandb.co.uk FaceBook Minions_shop Po House, Minions, Liskeard Cornwall PL14 5LE 01579363386 -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/listfaq