Freeview is broadcast on digital multiplexes. This means that, once broken down into a stream of bits, each television channel is combined into a single transmission of 1s and 0s. This means that reception is of the multiplex first if this is lost it affects all the channels in the multiplex in the same way.
The signal strength received by the box or TV for a particular multiplex from a given transmitter determines if the data can be received or not. So, a poor signal results in no data, an adequate signal in perfect data and a low signal in either none or all.
Poor digitalsignal levels do not result, as they do with old-fashioned analogue television, in a sub-standardpicture or sound. Poor signals often result in a perfect data-stream, but are prone to periods of no reception. Sometimes this will be for hours, but can also be several times a minute when caused by induction from fridges, freezers, central heating systems, two-stroke scooters, baby monitors and so on.
The RF connectors need to be in very good condition to work. There are two general types:
Factory-fitted connectors are very reliable as they cannot easily be taken apart, but they can be damaged by wear and tear. On the female-type the central section is often composed of two parts which can often be forced apart, resulting in a poor connection you can push them back together if this has happened with a pair of tweezers. On male connectors if the central pin is damaged, you will need a new cable. If there are any loose partials in the connector, remove them.
Another problem with these cables is that quite easy to sprain the connector at the back which causes little obvious external damage, but disconnects the internal connection. This happens often when a set-top box is pushed backwards into a cabinet.
Hand made cables can also suffer from similar problems to factory made ones and they are also prone to accidental damage from a cable being pulled. If such a connector is not firmly attached to the cable, the connector may need refitting.
Make a visual check of the cables. There are a few basic checks:
If the cable has been slashed or cut, it will not be very effective or reliable. If such a cable is fitted externally, this can allow rainwater to enter the cable and this will reduce the signal levels.
You can easily damage an RF cable by crushing it, for example in a door. If the outside of the cable has a permanent kink in the cable or has been very tightly looped, this could be the site of damage.
You can make a visual check of the route between the aerial and the transmitter. Any form of obstruction will damage the digital signals. In particular trees coming into leaf, as these will leech the signal before it reaches your aerial. This applies to both trees adjacent to the aerial and at a distance.
Another common problem in cities is building work. A large crane will often change position many times during the day, and if this is between your aerial and the transmitter this can reduce the signal levels in an unpredictable way.
If your system uses a booster, the power may have failed. Check the fuse to the power to the booster.
For the last week or so BBC & ITV SD Channels from Tacolneston have suffered contiual digital break-up. (Channell 55 predominantly) all the others are fine. TV's report signal strength high, signal quality poor. It also seems slightly intermittent getting worse in the evening.
It could of course be one of my boosters packing up!
any reported problems?
Pete Dilloway: You havn't given a postcode, so we are reduced to guesswork, but since you report high signal strength with low quality, it sounds like your signal is too strong. Try bypassing any booster, etc. You could try and find the 'too much of a good thing' page on this site, but the search function is currently disabled!
I appear to have lost the Dave and Pickchannels. They disappeared a couple of weeks ago (blue screen saying no signal) and when I retuned they disappeared from the epg list.
I have tried turning tv off and unplugging aeriel and retuning with no aerial to clear the information and then retuning with aerial but no change. postcode is 0X16 2AP and I am on the Oxfordtransmitter.
Alan Cooper: The channels referred to along with Sky news (132) are transmitted on Oxfords COM5 Mux Ch59, if Sky news is also missing? go into your TV or boxes tuning menu / manual tune and enter Ch 59 into the box, but pause at this point to see if anything is indicated on the strength / quality bars, if it is press scan or search.
By the way, the pause procedure does not work on some brands of equipment, and so press search (or scan) even if nothing is indicated.