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Re: [LUG] OT: Freeview interference

 

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




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