For "Interference at specific times of day" click HERE
Satellite TV picture Interference Problems
This article applies to UK and European transmissions.
My advice is always "Try your Digibox on a known good dish system". This advice often results in the complaint "I don't have any friends or relatives" or "There are only 40,000 expats in Cyprus and I can't find anyone else with a Sky system". In that case, bring the Digibox back to the UK, if necessary, and get a dealer to test it in his workshop.
If you have established that your Digibox is definitely NOT faulty, read on.
If your TV interference looks like tyre tracks, read THIS ARTICLE.
For advice about "sparklies" on analogue transmissions, please read the "Sparklies" FAQ on our analogue web site.
(Faults that you might be tempted to describe to me as "poor pictures" are totally meaningless. I have no way of guessing what you mean. Be sure to tell me the history of the problem and a precise description of what you see/hear and when, under what circumstances. But read the following page first. The answer may be here).
Digital pictures don't suffer from interference in the form of "sparklies" or "grainyness". "Lines on the picture" might be caused by an internal fault if the digital receiver is old but most interference will be external - getting into the RF cable after the signal comes out of the digital receiver.
Check your connection method and check our list to make sure your TV set is compatible with Sky Digiboxes. Better still, check the list before you buy the TV! Click HERE to see the list. (It's a large file so give it time to load).
Instead of "sparklies" you will see the picture "freezing" or breaking into coloured squares. This effect can be caused by a weak signal or a problem with the dish, LNB, cable or connectors. (Graininess and ghosting can not). To decide which, you need to test your digital receiver on a known good dish system. If it's OK there, then it's probably not at fault and you should look at the rest of your installation. If the fault has occurred only recently, think about anything that you may have done, changed or added which might have caused the problem. Never change more than one thing at a time unless unavoidable.
A lot of problems can be eliminated completely by replacing substandard satellite and TV cable with good quality, double-screened cable, including RF leads.
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| You should also avoid wall plates because the tiny stub of exposed centre core wire will act as an aerial and transmit or pick up interference. Run both TV and satellite cables directly into the satellite receiver without any joints. |
If a wall plate must be used, throw away the guts and glue a female plug in the hole. Fit the cable end into this plug and solder the inner core. In this way, you keep the core fully screened. This applies to both "F" wall sockets and UHF wall sockets and surface boxes.
SatCure stocks wall plates with the correct fittings - unlike the one in the picture! Interference lines on Satellite channels only can be caused by too strong a terrestrial signal. Unplug the roof aerial cable to check. Try fitting a UHF attenuator between the TV aerial cable and the satellite receiver UHF input socket. Interference from digital terrestrial transmissions can make your satellite picture look "grainy". Try setting your satellite receiver RF output to a different UHF channel number or use a Scart lead.
If you set the satellite receiver UHF output frequency to a different UHF position, be sure to retune your Video recorder and TVs to match.
Interference on analogue terrestrial Television channels may be removed or reduced by fitting a mast-head amplifier to the TV aerial. If the terrestrial signal is already strong, you should also fit a UHF attenuator to the satellite receiver aerial input, as described above.
Interference or patterning on Digital pictures should not occur. If it does, connect the digital box to your TV via a Scart cable that has screened video wires inside. Disconnect wire 19 at the end furthest from the Digital receiver (the TV end - label it!). This wire can cause "ghosting" or interference lines so eliminate it. If your TV accepts RGB input, select "RGB" in the digital receiver menu and see if that helps.
Ghosting is usually caused by crosstalk interference between wires inside a Scart lead or between coaxial cables that are run too close together and/or have insufficient screening.
Double-screened coaxial cable should be used for ALL coaxial connections nowadays since this is required for digital signals. You should also use the shortest lengths of cable that are feasible for your particular installation. SatCure stocks Scart leads as short as 18" (0.5 metres). Also longer, lockable leads that can't be pulled out accidentally - a frequent cause of "blank screen" or "no audio".
For all cases of interference, you should test the receiver in a different location before assuming that it is faulty.
If you are absolutely certain that the interference is within the receiver itself and if it has appeared gradually, then the most likely cause is electrolytic capacitors which have aged because of heat. All electrolytic capacitors have a limited life and need to be replaced periodically. The largest capacitors in the power supply are most likely to fail first. A RELKIT capacitor kit is available from SatCure for most models.
You can carry out tests to narrow down the likely cause of interference:
- Unplug the TV aerial cable and RF output cable from the satellite receiver and plug them together to bypass the satellite receiver and note the result.
Now unplug the satellite receiver from the mains power supply and note the result. - Unplug any scart or Phono (RCA) connections from the satellite receiver and use the RF connection instead. If there is an improvement, try using a very short, partially-wired scart lead instead. Make sure that no unused wires are connected inside the scart lead; for example, pin 19 of the plug that goes into the television should never be connected because some TV sets send a delayed video signal back out on this wire.
- Bypass the video recorder and connect the satellite receiver direct to the TV.
- Bypass the satellite receiver and connect the TV aerial direct to the TV.
- Move the satellite receiver as far from the television as possible.
- Make your own RF leads from double-screened satellite cable or order some from SatCure.
- Replace the television aerial cable with double-screened satellite cable or, if this is not possible, replace as much of it as you can reach (ideally, the bottom 3 metres at least). Use a proper connector if you have to join two sections of cable. Waterproof it if it's outside (self-amalgamating tape).
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Interference at specific times of day
Occasionally you might experience degradation or complete loss of picture during certain hours - repeated each day or each week. Sometimes this affects ALL channels and sometimes just a few. First, make sure it's not just a problem of ALL vertical or ALL horizontally polarised channels affected. The usual cause of time-specific interference is a local microwave transmitter. This might be a neighbour's police radar jammer in a car or a source several miles away and your dish might be seeing a reflection of the actual signal - it doesn't need to be directly in line with the offending transmitter. The transmission could be from a local company which transmits its weekly report back to head office every Friday evening (for example). You will probably not be able to locate the cause. To test this theory, place your dish (or another dish) on the ground and align it. Connect it to your receiver. If the interference disappears, reposition the dish in a permanent position where it does not suffer from the interference. The shielding effect of walls can be significant but they can also reflect. Keep the dish as low as possible.
Another cause of interference is your neighbour's TV. TV sets are notorious for generating interference so check to see if your neighbour's set is close to yours on the other side of the wall. If it is, ask him to turn it off while you check.
In parts of Europe, the signal becomes weaker in the evening because the satellite reorientates itself to align its photovoltaic cell arrays with the sun. This can alter the transmission "footprint".
Interference from "Snooper" type radar detectors in cars is quite common. It will tend to "wipe out" specific programmes but only when the car is present.
Intermittent interference can also be caused by nearby electrical equipment such as dimmer switches, mercury vapour lamps*, sodium lamps*, microwave ovens, transport systems (electric railways or even diesel railways if they create electrical interference at a high frequency) and farmers' electrified cow fences. In all such cases, if the source of the interference can't be removed, then you must move your dish and cable as far from the source as possible. Mount it so it is shielded by the building, if possible. Make sure you are using new double-screened cable.
*Street lamps are a common cause of interference and the offending one might not even be in your street! If you suspect a lamp, take a walk with an portable A.M. radio to track it down. Tune the radio off-station so the interference can be heard above the background hiss.
If the interference is from a central heating boiler thermostat it will usually occur for a few seconds once every twenty minutes or so. We sell a boiler thermostat suppression capacitor which might help.
Portable DECT telephones and mobile (cell) phones can also interfere. Remove power from them to check.
Interference with Motorised Systems
Interference on motorised systems can have two main effects:
1. The positioner counts too many pulses and does not reach the satellite position. This is often blamed on the positioner as "loses its memory."
2. The motor causes interference on the TV picture and possibly on neighbouring TVs and radios.
The main cause of interference is the use of unscreened caravan cable or telephone cable.
The remedy is to use proper screened cable. The motor wires should have a screen as a minimum. The pulse wires and polariser wires should also be screened separately. All screening braids should be connected to ground at the receiver only. They should not be connecting to the dish. The dish assembly should have a separate ground connection to a copper rod in the adjacent soil.
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DIGITAL CABLE?
>With regard to the installation of the Digilink extender unit, just a quick question.
>Can I use ordinary aerial cable (which I have about a 25m roll left after
>installing a new TV aerial) or does it have to be higher quality (like
>the cable used for the satellite installation) ?
Interesting question but there's no quick answer. In the good old days before satellite, you could get away with almost any crappy coaxial cable. However, satellite receivers tend to radiate some interference, locally, so it's best to use good quality, double-screened cable within a couple of metres of the satellite receiver - otherwise its radiated "noise" gets into the cable through the poor outer screen. This problem also suggests that coaxial wall sockets should either not be used or should be of the fully-screened type. In addition, the down-lead from the TV aerial should be double-screened, at least near the satellite receiver. If you are receiving digital terrestrial signals (ITVdigital) then the whole length of aerial cable must be double-screened. Bear this in mind when fitting or replacing cable. Soon it will *have* to be double-screened when analogue TV transmissions are shut down.
What's the best cable? Read the review
Terrestrial digital TV transmissions are terribly susceptible to problems with car ignition interference and of switching transients within the building. This fact dictates that the complete run of cable from the aerial down to the first box that it plugs into should be double-screened and *without* any in-line connectors or sockets. NO coaxial cable should be run close to any mains power cables since these radiate switching transients which can knock out a digital picture and even "lock up" the receiver.
Taking both factors into account, it seems that ALL coaxial runs within the building ought to be of double-screened cable *without* any in-line connectors or sockets. If that is impractical, then any socket/plug arrangement should be fully screened. See SatCure Satellite accessory pages for suitable cable and connectors.
So, in answer to the question: if the installation already uses single-screen cable you can try it and see if it is OK. If it is not OK or if you are installing new cable then *always* play safe and use the best double-screened cable available.
If you need to use a distribution amplifier then at least two factors must be considered.
1. It must be suitable for digital signals, if that is what it is distributing. (The signal from the terrestrial aerial must be considered "digital". The RF output from a digital box is currently NOT digital - goodness knows what it will be in the future when all TV sets accept a digital signal).
2. It must be able to pass the signals from a "Remote Eye" or Digilink extender - even if you don't use one now, you might want to in future. Alternatively, you could fit a "Bypass" unit but this *might* have a detrimental affect on the signal because it adds two in-line connectors.
> I have seen it all now !!
> I have just returned from a long time customer of mine who has
> recently taken up SKY's £20 digital offer. The installers turned up
> with an Amstrad DRX100 receiver, connected it up to the existing
> 60cm dish/LNB and left - leaving the customer with severe patterning
> on terrestrial channels. The customer phoned SKY to report the
> problem who duly sent an 'engineer' some two weeks later (??). He
> said that there was nothing wrong with the digibox and left.
> Out of desperation they called me to see if I could do anything to
> help. I noticed that just moving the digibox around caused the
> patterning to vary. Unplugging the phone line from the digibox
> reduced the patterning by 50% so I re-routed all the leads and made
> up new RF leads between digibox/VCR/TV using CT100 cable, resulting
> in further improvement. Unfortunately there is still significant
> patterning on terrestrial channels 49 & 52 and moving the digibox RF
> converter frequency has no effect. Obviously, this DRX100 is proving
> to be a very useful 'transmitter' and I believe that a replacement
> digibox will be the only cure.
> John
I have never been happy with the mains protective earth connection on the DRX100. You'll see my comments at:-
http://www.satcure.co.uk/drxtuner.htm
In addition, if the 13A mains socket has no earth connection then that will make matters even worse. You think this is impossible? Well, a few years ago I passed a "Martindale" type 13A test plug around my street of 21 houses. Each householder reported back to me in writing, on a form. The result was over 50% of sockets had an intermittent or non-existent earth connection. All sockets involved had been manufactured by Volex (about 25 years ago) and the "spring" clips were made of brass instead of phosphor bronze or berillium copper! One socket also had a live wire that was loose and caused arcing - with the eventual demise of the television set!
The patterning you describe is normally to be found where the aerial signal is borderline/weak. The usual answer is to fit a masthead amplifier (or an amplifier in the roof space as close to the aerial as possible) and an attenuator at the Digibox. Most of the interference gets into the TV aerial downlead in the last couple of metres so the attenuator helps to reduce this. However the entire aerial coax *ought* to be of the double-screened type to prevent this problem.
What's the best cable? Read the review
Using CT100 will increase the signal available from the aerial and also reduce the input of interference. Make sure that there is either NO wall plate for the TV aerial or else use the 'F' connector type that I stock.
Please see my accessories catalogue and my "F" connector page.
Finally
It is impossible for me to guess at the reason for picture interference if it is caused by your faulty installation. These notes are designed to help you to solve the problem by yourself. Please read them carefully. Carry out the tests and make notes. If you still need to write to me, be sure to explain your tests and test results in ordinary non-technical English. Paint a picture in words. I can not guess what you are seeing with your eyes. You must describe it in detail, without using "looks like" phrases or technical terms. Use ordinary words to describe what you see. Be sure to mention colour, size, thickness, orientation, position, quantity and movement of interference lines. (If you are not English, simply do your best. I understand a little German and a (very) little French and Spanish.) It is also important to tell me exactly what equipment you have and how it is all connected together.
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