From time to time people find that their Freeview box, integrated set (idTV) or Personal Video Recorder (PVR) has lost many channels without any apparent changes.
There are a number of factors to consider
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 digital signal levels do not result, as they do with old-fashioned analogue television, in a sub-standard picture 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.
For reliable and effective Freeview reception, a rooftop aerial is required. It is hard to make a visual check of such an aerial without putting yourself in potential danger.
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.
There are two main weather problems that effect Freeview reception.
neil: If your using Mendip, then it has Com7, so you should be getting Talking Pictures, BBC4 HD, C4 + 1, etc. Unless you havn't got an HD tuner, in which case, your going to get zip. If you do have an HD tuner, then check signal strength - you might have a problem with your system, and since that mux is 25% less powerful than the rest, it might have vanished first.
The freeviewreception here in Dorset (Postcode area DT10) has deteriorated considerably in the last few weeks. Has the Txmitter power been reduced or have other factor(s) appeared which would cause this?
David Rigby: Transmit power has never been reduced on any UK transmitters since digitalswitchover, except temporarily when necessary for engineering work. You probably have a loose or damaged cable or joint somewhere, or perhaps water has gotten into your aerial system. Start from behind the TV and follow the aerial cable back as far as you are able to safely access. Swap out any jumper leads for a new or known working one. Unscrew any wall plates and check that the cable is securely connected at the back with no loose strands from the outer braid touching the inner connector.
BBC4 HD and several other channels are on Rowridges two lowest-powered multiplexes - namely 10,000 and 24,400 watts. As I only have an indoor aerial I can't receive any of the channels on the two muxes.
Strange, though, that during the Olympics BBC4 HD returned - with no problems. Now that the Games are over the HD channel has disappeared.
Is there any way for me to appeal to the 'powers-that-be' that run Rowridge to increase the power to these two muxes?
All other channels, on the 200,000 watt muxes, are fine. Installing an external aerial isn't an option for me.
John H: You're referring to the COM7 and COM8 multiplexes which are temporary services and are broadcast at lower power than the permanent multiplexes at nearly all of the 30 transmitters that carry them. They won't receive a power increase as this would cause interference with other transmitters broadcasting on the same frequencies and will be closing in 2020. BBC4 HD was moved to PSB3 temporarily to increase it's coverage during the Olympics but was moved back to it's normal home on COM7 yesterday.
From what you're saying I can't receive COM7 or COM8 via my internal aerial. If these are due to close in 202 what will become of the stations they carry?
Obviously, I may have seriously look into an getting external aerial - and that's going to be difficult.
If I wasn't surrounded by trees I'd ditch Freeview in favour of Freesat :-(
John H: By 2020 all the permanent multiplexes will have switched to DVB-T2 transmission mode (currently used by PSB3, COM7 & COM8) which will create plenty of additional capacity for the channels currently on COM7 and COM8 to move to. I would suggest you check your reception prediction via the link below (check the box for detailed view) before going to the expense of having a new aerial installed to check that you have a good chance of receiving COM7 and COM8 at your location.