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-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.
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.
Julian Parker: It wouldn't necessarily be due to proximity.
When the automatic tuning scan is run, a receiver scans or listens to all frequencies so as to see what it can find. At the end, it makes a 'decision' of which transmitter to go with, should more than one be found.
In this case, evidently and for whatever reason, the decision is to go with, I assume, Wenvoe.
The workaround may be to have the aerial unplugged during the part of the scan where Wenvoe's channels are, although they are only just below Mendip's.
Have the aerial unplugged up to about 55%. If, having done this some channels are missing (because the aerial was out until a bit too late) and there is a manual tune option, then add the missing ones manually:
COM4 - ITV3 etc is on UHF channel 48
PSB1 - BBC One etc is on UHF channel 49
Julian Parker: This will happen in the Bristol Channel area because the Wenvoe transmitter (BBC Wales) uses lower frequencies than the Mendip transmitter (BBC West), this results in the scan finding Wenvoe channels first, which are duly entered into the channel list, then when Mendip channels are found any which carry a variation will be placed at the end of the channel list - usually in the 800s, as the LCN (normal) positions are already occupied. If the Mendip signal is stronger than the Wenvoe signal some tuners will overwrite Wenvoe channels with identical content to store the transmitter with the strongest signal, which sometimes results in an assortment of channels from each of the available transmitters. The direction that her aerial is pointing will usually determine which transmitter offers the strongest signal, but in the first instance channels on lower frequencies are always scanned first.
Thank you everyone who have replied with advice. My friend has advised me that her missing programme appears on channel 800 as suggested and the stronger channel appears on BBC1. When I have time I will go down to Bristol from Cheltenham and do a programme position swop for her.
Many thanks for all your help.
Julian Parker: You will probably find that all services on PSB1 are 'wrong'. That is, the Mendip ones are in the 800s. It probably won't just be BBC One that is wrong although it will be most obvious as it has regional variances, as does BBC Two sometimes.
I live in postcode G61 2LU. I fitted and ran the Antenna / cables myself and also a booster. Every now and then I get a poor reception on BBC. (Perfect through Virgin box. I now also get a pooer reception on other channels. I will check the connection @ antenna but do you think I need a high gain one.
Martin: I am inclined to think that the reason your problem is more likely to be caused by the signal reaching you suffering from intermittent periods of being partially obstructed by trees, these being in abundance in your area, and should this apply then a high gain aerial is the last thing you want as its sharper focus would make the situation worse.
However, I wouldn't as yet try altering anything until you verify if others in your "immediate" vicinity (no more than a couple of houses away) are also suffering from the problem as its very likely that they are and so its worth checking.
Further advice dependant on findings.
By the way the Virgin box will not be affected as its a cable device.
Hi, I cannot pick up BBC channels since April 10th on the 15" Technika TV in the bedroom, even when I used the main aerial downstairs I had the same effect. The other freeview channels seem unaffected.
After the 10th April changes, my old Freeviewbox will not store the channels. This means that I have to "tune" it every time I turn it on. This never happened before 10th April, but it happens every time now. There were various messages on screen about 10th April, but surely, I do not have to retune it each time I turn it on? It takes me back to 1960 when I had to wait for ages before one of the two stations was selected!
Peter: This could possibly be caused by the common reason of a box having picked up more channels than its memory capacity can store hence they are lost every time the box is switched off.
To make sure that nothing is stored go into the boxes set up menu and look for either factory reset / default setting / first time installation and press on whatever is seen, then after completion of same carry out another auto-tune.
Bbc 1 and 2 have started to break up, the picture and sound just drift in and out. All other channels work fine.
Also bbc 1 has disappeared from its channel 1 on the channel listing as has bbc 2 only to be found on channel 823 but as a bad picture.
Pam: Yes, this was because your TV had picked up more channels that its tuners memory capacity could store hence they dropped out again when the set was switched off, "first time installation" before tuning having cleaned out the tuners memory thereby allowing more storage capacity for the channels actually required.
Since a few weeks ago reception of all the HD channels available from the IOW transmitter have disappeared. I have tried retuning my TV (Sony 46HX853) but they have not come back. I am still receiving the ordinary channels on CH24 & CH27. Any help would be gratefully received.