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Freeview signals: too much of a good thing is bad for you
If you have a high-gain aerial or use signal amplifiers, it is quite common to find that the high-power digital signals provided after switchover will overload your Freeview equipment - and can appear to be "weak signals".
Most people will experience nothing but simplicity and joy with the digital switchover - the process that turns off the old five high power analogue signals, and the existing six low power digital services and replaces them with six new high power Freeview multiplexes.
For those with problems, there are generally three issues.
Eliminating other possible problems first
The first is that very, very old equipment will not function with the digital signals split into 6,817 sub-signals, as it was only designed to work with 1,705 sub-signals. This is known as the "8k mode issue" - see TVs and boxes that do not support the 8k
Transmitters have much more digital power after switchover
At most transmitters, the digital signals after switchover are considerably more powerful than before. This was because when the analogue and digital services ran together, the digital services were kept low to prevent appearing as snowy interference on television sets using analogue reception.
Here is an example, from Sutton Coldfield, of how the signals change at switchover:
4,000kW of analogue signals are turned off, and the digital services increase in total power from 48kW to 1,200kW - that is an increase of 25 times in numerical terms, also know as +14dB. (The reduction of -7dB from the analogue strength is intended - the digital services require less power to cover the same number of homes).
This large increase in power should cause no effect for most people. A stronger signal does not increase the picturequality (you need Freeview HD for that), sound levels - the only effect should be that more homes that are further away from the transmitter mast can receive a stable digital signal.
High gain aerials and signal boosters
However, many people have been tempted into buying one both high gain aerials and signal boosters.
High-gain aerials were very suitable for places where the Freeview signal before switchover was very weak indeed, but if you have one of these and you are located closer to the transmitter, you will probably now have a signal overload.
Generally speaking, signal booster devices are never really much use for Freeview reception, and much of the time they actually amplify the interference more than they do the signal, causing reception to get worse, not better.
How to tell if you have too much signal
There are almost as many ways for a Freeview box to display the "signal strength" and "signal quality" as there are types of Freeview box. Here are some of them:
Speaking generally, there will be two indicators:
One is signal strength - this shows the power level of the signal entering the Freeview box. Often "0" is the lowest and "10" the highest, but sometimes it can be a percentage, sometimes coloured boxes and so on.
The signal strength should be around 75% - more than this indicates too much signal.
The other measure is the signal quality and this is much more important to high-quality Freeview viewing. Any measures that increase this to the maximum will provide for uninterrupted viewing, lower values will result in "bit errors" that cause the picture to freeze and the sound to mute out.
One problem with over powerful signals is the overload can sometimes show as a low signal because the receiver circuitry will enter a "blown fuse" state to protect itself.
How to deal with too much signal
First, if you have a booster or amplifier - remove it from your system. Don't just unplug the power, as this will result in no signal getting though the device.
If you can't just disconnect the outputcable and connect it to the input cable, you might need a coax female-female coupler to connect two male connectors together.
If you don't have a booster or amplifier, you might have to fit an attenuator onto the cable. They come in two types, either a "single attenuator", around five pounds, or a variable attenuator, for around ten pounds. The variable sort has a knob that can be turned to select the required level of signal dampening.
Your comments are always welcome. Please use the form below to add your thoughts or questions to this page. We will get back to you as soon as we can.
linsey Sunday 30 December 2012 1:45PM Stourbridge
thanks. my post code is dy8 3xe will that help diganose the problem better. When I said I am close i may have missled you - not sure how close is good/bad, but brieley hill is only approx 3 ish miles away.
Glad of any further advice.
linsey: It is worth checking that your receiver is tuned to the transmitter that the aerial is pointing to. If your aerial is mounted with the rods vertical it is intended to receive from Brierley Hill, if rods are horizontal it is intended to receive from Sutton Coldfield. Both transmitters are in the same direction (53 degrees or NEish), so incorrect tuning is a possibility. Have a look at the frequency/channel being received for each of the muxes. B/H is 60-, 57+, 50, 59+, 55 and 53(HD). For S/C the UHF channels are 43, 46, 42, 45, 39+ and 40+(HD). These correspond to muxes carrying BBC1, ITV1, ITV3, Sky News and Film4 respectively.
SC's are in the 40s and Brierley Hill's 50s and 60. If it gives percentage as it scans, have it unplugged up to 55%. Or if it gives UHF channel numbers (21 to 69) during scanning, then SC's highest is 46, so wait until it's past it.
Louise Irvine Wednesday 27 March 2013 11:25AM Dundee
Hi. My postcode is DD4 7JE. We used to receive our signal from Tay Bridge but we've just had our communal aerial upgraded to receive from Tealing transmitter. Since the upgrade, 2 of the 3 TV's work great, but one, and our Youviewbox have good signal strength (45 - 60%) but picturequality is around 10% at best, and unwatchable. As we are so close to Tay Bridge transmitter, less than 1 mile away, could this be causing the loss of picture quality?
Craigkelly's three PSB channels are 27, 24 and 21, respectively.
If you find that your receiver is tuned to Craigkelly or Tay Bridge then these are on lower channels (lower frequencies) than Angus, so you may be able to unplug the aerial for the part of the scan that the unwanted transmitter broadcasts.
The scan runs C21 to C69. It may give channels as it scans, or it may give a percentage. Tay Bridge's highest is C47 and Angus' lowest will be C49 following the retune which is due on 17 April. Plug in at 55%.
Louise Irvine Wednesday 27 March 2013 2:03PM Dundee
Dave Lindsay. We're deffo receiving from Tealing, I checked with the guys who did the upgrade work. We've got a cheap powered indoor aerial, and we receive a fairly good signal, including HD channels from Tay Bridge on the TV that doesn't work on the communal system. Also, we were given the PSB's for Tealing to do a manual tune.
Louise Irvine: The thing with a communal aerial system is that one needs to establish whether the issue is with the system or the receiver. If it's the former then it's beyond your control and the responsibility lies with whoever maintains the aerial system.
I am assuming here that the aerial sockets in your flat are all part of the system and that you aren't provided with one, say in the lounge, from which you've run cables to the other rooms.
If these are sockets provided as part of the system then maybe you could take the troublesome TV to the other sockets and try it there. Maybe us a different aerial lead so as to disprove that as being a possible cause.
If the guys are still there then I would advise you put the kettle on and ask them if they wouldn't mind taking a look.
Louise Irvine Wednesday 27 March 2013 4:39PM Dundee
Dave Lindsay. We've tried everything, working TV's in all sockets, which are fine, non-working TV in all which is not. Yes we have a splitter as the aerialcable enters the flat, supplying all 4 aerial sockets.
The guys have already been back, and according to them and their "spectrum analyser" (not sure what the technical term for the equip they use) there was nothing wrong with our system. Hubby had installed a masthead amp at the point of entry, but this was removed by the aerial engineers, saying it had been wrongly installed. If it had, we wouldn't have got a signal to any TV, besides he used to be a TV engineer.
I'm certain we've tried everything, including purchasing of a double sheilded co-axial cable, but so far nothing has worked.
The only thing that I can think of is that the tuner in one TV and the Youview is particularly sensitive, and therefore picking up interference from somewhere, whether its Tay Bridge or electrical cabling in the property.
Louise Irvine: I don't think there's much more to suggest. It may be worth trying the troublesome TV directly into the aerialwall socket (without the cables that feed different rooms connected). Failing that, perhaps stick with PSB-only Tay Bridge via the set-top aerial.
From Angus, there are six broadcast channels (frequencies/signals), including the HD one. Does it affect them all?
hi, our bush digibox 500gb worked fine till the change over. we returned it to argos for the same . it still will not hold bbc tv picture . tv picture from airial is great.signal strength on tuning is low but if i put airial into rf out on digibox the signal increases but still will not hold bbc1 . can you help?argos helpline is useless. i did see that looking for bbc1 durther up the ch list may work
m newhouse: The issue of receivers 'forgetting' channels when they are powered down usually happens where they have run out of tuning memory. The forgotten channels are picked up last during the automatic tuning scan and also the signals from other transmitters have been picked up before. The trick is usually to prevent a receiver from storing the signals from other transmitters so as to have enough room for the wanted one.
Without knowledge of your location (preferably in the form of a postcode or nearby postcode such as that of a shop) and transmitter it isn't possible to tell whether this may be the reason for your difficulty.
It is rare for an aerial to give 'too much' signal without a booster/amplifier unless you are very close to a main transmitter.
In analogue days you would see strong cross modulation patterns on the screen but with digital you can only go by the signal strength and quality guides. If the signal is too strong then the Strength will be 100% but the quality will be very low. You can check it by inserting a coaxial attenuator in the aerial lead, preferably at the TV UHF input for this test purpose. They are available with different attenuation, typically 6dB, 12dB or even 18dB. If by trying one the strength stays high but the quality improves significantly then there may be too strong a signal.