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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".

If you have a high-gain aerial or use signal amplifiers, it is
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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

It is also common that people do not clear out the old channel list (by selecting "first time installation" retune, "Factory Reset" or "Shipping Condition") before doing an "autoscan" for the available broadcast frequencies, and this results in everything from missing channels to no subtitles, programme guide, wrong channel numbers and no text services. If you can't find how to do it see either Freeview Retune - list of manuals or do it this way: My Freeview box has no EPG, is blank, has no sound or the channel line up is wrong .

A third problem is caused by having signals from more than one transmitter - see Digital Region Overlap.

The final very common issue is "too much signal".

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 picture quality (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 output cable 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.

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Wednesday, 8 February 2012

11:14 AM

Iain: Loft aerials are not recommended for reliable Freeview reception.

However, to answer your question, then yes, you should be able remove the booster from your system when the signals are all at full power - which will be today for the BBCA service, in two weeks for D3+4 and Freeview HD and on 18th April 2012 for the rest.

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Briantist's 38,915 posts GB flag
1:04 PM

Thanks Briantist. I understand about loft aerials but, perhaps because we live on a hill and can SEE Hannington on a clear day, this has never been an issue before. Am I right in thinking that replacing the booster with a simple multi-way splitter is unlikely to work properly for all channels until after April 18th?

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Iain's 2 posts GB flag

1:09 PM

Iain: Yes. However there are problems at Hannington at the moment, so you should wait until this evening for them to fix them.

The best thing to do is to wait and see if you have a problem with the booster when the signals are working correctly.

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Briantist's 38,915 posts GB flag
Friday, 10 February 2012
Lance Spencer
2:44 PM

What a difference!
When I retuned the set on Wednesday evening the new BBCA mux was 10/10 for strength AND quality.

On the very cold clear nights the BBCA mux reduced by 2 points.. I'll have to keep the amp in circuit for the moment though until the 22nd when the other mux's come on-stream.

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Lance Spencer's 12 posts GB flag
Wednesday, 15 February 2012
11:34 AM


I live near Hindhead on the Surrey/Hampshire border and did a rescan last night on prompting. All channels are fine except the BBC channels (1,2,3,4, News 24 etc) on which the signal strength is good (c.75%) but the quality is low (10-20%) and the transmission is very jumpy and unwatchable. I have a high gain aerial...and booster (I think!).

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Deb's 4 posts GB flag
Dave Lindsay

12:50 PM

Deb: If the booster is one that is connected to the aerial lead where it comes into your room, then remove it.

If, after doing this, you get no signal whatsoever on any channel, then perhaps it is not a booster, but a power supply for a booster which is located on the roof with the aerial. The reason you would get no signal in such circumstances is because the booster is still connected (on the roof) but is not powered (as you've removed its power supply).

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Dave Lindsay's 5,724 posts GB flag
2:14 PM


Thanks for the (speedy) reply. So you are saying I should try to remove the booster from the 'circuit'?

I interpret your second para as detailing a permutation relevant when the booster power supply is in the house but the booster is on the roof with the aerial.

It still seems odd that this has happened on a day (14th) on which Hanningtone wasn't changing. I did a re-scan on the 8th/9th immediately after the first part of the Hannington change and all was ok.
Regards, Deb

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Deb's 4 posts GB flag
3:01 PM

Problem solved - but only by disconnecting the BT Vision box from the circuit (it was that which prompted the rescan).

Have connected aerial into TV (40 inch Sony 723NX something or other) and tuned in the digital channels. All clear as a bell. No problems whatsoever.

So I assume the problem is with the BT Vision box somewhere. Ah well. Maybe time to move onto something more robust.

Thanks for your support Dave.

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Deb's 4 posts GB flag
Dave Lindsay

4:29 PM

Deb: You have narrowed down the source of the issue. I wouldn't be of the opinion that there is a fault with BT Vision box just yet.

I'm not familiar with the BT Vision box, but in general terms I know that it connects to the internet either wirelessly (using wi-fi) or wired (using a network cable, sometimes routed over mains cables using "Powerline" adaptors or similar).

If you are connected using wi-fi, try disabling the connection in the box's settings. If you are connected using a network cable, unplug the cable from the box and unplug it at the other end. If you have a Powerline adaptor adjacent to the BT Vision box, then unplug it from the mains and try the reception of TV channels on the BT Vision box.

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Dave Lindsay's 5,724 posts GB flag
7:09 PM

It seems that the explanation is as follows:
(i) My aerial is pointing at the Midhurst transmitter (not yet gone through DSO) and there are engineering works on that transmitter which might explain the signal break up. It took several hours to realise I used Midhurst and not Hannington!
(ii) the upgrade of the Hannington transmitter has created 20 new BBC channels (800-820) which are not disupted and so can be used whilst the 'normal' BBC channels are less than perfect

I'm assuming that once the engineering works are complete at Midhurst the normal channels will return to full quality. And be even better once Midhurst has been through DSO.

(Re Vbox - mine is connected through adaptors not wi-fi)

Thanks for your input Dave. The above came out of a lengthy discussion with another on the BT forum.

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Deb's 4 posts GB flag
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