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Written by Chris Hallamore
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LOST CHANNELS WITH BBC AND ITV DISAPPEARING EARLIER IN THE EVENING THAN PREVIOUS YEARS DUE TO LNB FAILURE
By Chris Hallamore
The long hot summer is coming to an end and watching telly will become more important as the long nights draw in. In many homes the BBC and ITV channels are breaking up and disappearing sooner in the evening than in previous years.
The problem with channel five missing is well covered by John in another article in this issue and is not caused by a faulty LNB.
It is common knowledge that here in Valencia we have a poor signal from the Astra 2d satellite transmitting the BBC and ITV channels. Channel 4 and five are also transmitted from Astra 2d but these channels can be received from the Astra 2a satellite. To receive the BBC and ITV we need a big dish properly aligned with an LNB functioning a hundred percent.
Most of the big dishes installed have been in place several years, Most of them have very sound bases (the poor bases were renewed) and they are securely tightened and with proper installation there are very few valid instances of the dish moving on the support due to wind. From the installer’s point of view, quite often the owner is the culprit of misaligning his own dish.
The most likely cause of the poor reception of the BBC and ITV channels are the Invacom lnbs. These lnbs are arguably the best on the market for use on big dishes. However after several years they don’t function as new and need to be replaced. A degraded lnb will still receive the strong signals from Astra 2a (sky news and sports) but will be ineffective on the weak signals from Astra 2d (BBC and ITV) There are other makes of lnbs used on big dishes but since there are very few in use I can’t comment on these.
The invacom lnbs are available with single, twin and quadruple outlets. The twin LNB performs better than the single and the quad is marginally better than the twin (this only applies to the two inner outlets).
If you have a faulty invacom LNB with a single outlet, I would recommend changing it for a twin.
Obviously it is wise to use a professional installer to change the lnb. They will test the signal before changing the lnb and then replace the lnb with a new one and test the signal again and if there is no difference clearly the fault is not with the lnb and you won’t be charged for a new LNB.
If the lnb doesn’t have a plug in the throat of the feed horn it is common for an insect in the autumn to use this as their hibernating home and this will cause loss of signals at the very least. Be very careful checking this out as bending or distorting the rods holding the lnb will cause more damage than the insect. Using a mirror and a torch look up the throat and if there is an occupant. Mark the position of the clamp that holds the feed horn and remove the lnb from the support. Then remove the feed horn from the lnb. Inside the throat of the lnb are brass pins if you bend these in cleaning, the lnb will be rendered useless. Be sure to return the lnb to its exact position, a few millimeters out of position will decrease the signal.
For the D.I.Y experts you have to test the signal on your digi box to determine the state of your lnb. Some digi boxes give consistent readings and others are imperfect. The signals being transmitted are basically vertical or horizontal polarities. However these polarities are split as vertical high and low and horizontal high and low. Therefore you have to test the signal on a wide range of channels. The lnb may be working 100 % on some frequencies but poorly on others depending on the polarity.
Until next time
For more information call Chris on 680 357 586
www.swiftbox.net
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