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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
published on UK Free TV

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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Comments
Wednesday, 15 February 2012
Dave Lindsay
sentiment_very_satisfiedPlatinum

10:46 PM

Deb: I would suspect that the BBC channels in the 800s could in fact be the Midhurst ones.

Different pieces of equipment behave differently when they encounter duplicate services from adjacent transmitters.

On the automatic tuning scan, the new full strength BBC services from Hannington will be found before those of Midhurst which are on a higher frequency. *If* the BT Vision box picks the strongest BBC services (rather than the first it finds), then *perhaps* that is why it has done what it's done (if it has put Hannington BBC One as logical channel 1 and Midhurst BBC One in the 800s).

The way to find out which you have is to look at the signal strength screen for the UHF channel number (most boxes give this information).

Go to BBC One. Hannington's is on channel 45 and Midhurst's is on channel 56 (to move to 55 on 29th February).

I understand that the BT Vision box doesn't allow manual tuning with is very poor. However, there is a possible workaround.

Hannington uses channels 39 to 47 (and this will be the case after it completes switchover). Midhurst uses channels 56 to 65 (which will be 50 to 62 after switchover).

The trick is to run the automatic tuning sequence with the aerial unplugged for all bit the frequency range that it is scanning Midhurst.

If it gives UHF channel numbers when it's scanning (they run 21 to 68) then plug it in after 47 has passed. If it doesn't give channel numbers and only gives a percentage progress, then plug it in at 57%.


The irony is that the message you received about new services referred to the BBC services from Hannington that had moved. Had the message been ignored, then there would probably have been no issue now.

It may or may not tell you to retune on 22nd February when Hannington completes switchover. If it does, then you should ignore it.

For Midhurst, retuning is required on the following dates:

1. 29th February: Switchover stage 1 BBC standard definition services move channel and go on full power (to the one previously occupied by BBC Two analogue).

2. 14th March: The rest of the digital services move and the other three analogue services are turned off.

3. October 2012 (date unpublished as yet): some services changed channel.


Throughout all this, when retuning your BT Vision box, plug the aerial in after it has scanned channel 47 or at 57% in order to pick up all its services.

link to this comment
Dave Lindsay's 5,724 posts GB
Saturday, 18 February 2012
R
rebecca
7:42 PM

hi, i have just moved to crystal palace, and my old tv and digi box were working ok. now i have have bought a new HD tv an cant get a reception on most channels and heavy pixelating on others, and am so tired of moving the ariel about that i dont even turn it on any more and beginning to regret the expense of buying a modern tv ! is there anything i can do that wont be expensive or involve climbing onto the roof ? !

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rebecca's 1 post GB
Dave Lindsay
sentiment_very_satisfiedPlatinum

8:03 PM

Rebecca: I think that the most likely answer is too high a signal level. As per the instructions at the top of this page, you don't want any amplification (no booster connected). If you have one and you have removed it, then you need some attenuation; this is to bring down the level of the signal (the opposite of what a booster does).

In April at switchover the power of the transmitter will be increased ten-fold, so it is worth fitting an attenuator, even if reception is OK without it.

If your set-top aerial has a booster built in, then it needs turning to minimum or perhaps replacement with a non-powered aerial.

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Dave Lindsay's 5,724 posts GB
Dave Lindsay
sentiment_very_satisfiedPlatinum

8:08 PM

Rebecca: Here's one example of the type of device you need:

LABGEAR VARIABLE DIGITAL TV AERIAL SIGNAL ATTENUATOR 0 - 20dB | eBay

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Dave Lindsay's 5,724 posts GB
Wednesday, 7 March 2012
T
Tony Hill
sentiment_satisfiedBronze

11:32 AM
Dorchester

Just carried out Rowridge retune (Phase 1). We are on the edge of the transmitter coverage area in Dorset (just a few miles East of Dorchester). BBC channels on my Sagem Freeview box show Signal Strength of about 75% and Quality about 95%. Previously Strength was about 55%.

However, we do have a masthead amplifier - no signal would have been received before without it - and assume that we need to keep it. Is that right?

I also assume that with the increased strength we would be OK for Freeview HD - is that so?

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Tony Hill's 62 posts GB
Briantist
sentiment_very_satisfiedOwner

11:34 AM

Tony Hill: You may need to remove the masthead amplifier - see the above article - but not with the figures you have given.

Freeview HD requires no extra signal strength for reception, but you do need the correct receiving equipment - see Are you really watching free TV in high definition? | ukfree.tv - independent free digital TV advice

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Briantist's 38,844 posts GB
Thursday, 8 March 2012
N
Nick Flowers
9:59 AM

I retuned to Rowridge on 7th March and have not seen a significant increase in signal strength. Is the increase in ERP going to happen after the second retune on 21 March, or should I start to look for faults in my set up?

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Nick Flowers's 3 posts GB
T
Tony Hill
sentiment_satisfiedBronze

2:29 PM
Dorchester

To Nick Flowers:

Where do you live? My strength now about 80% in far west of the coverage area.

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Tony Hill's 62 posts GB
N
Nick Flowers
4:35 PM
Chichester

I live at PO18 9NF. Freeview has been pretty good here, except when it rains when you can forget it. I have noticed on the signal strength meter of my TopupTV PVR that the new BBC channel 24 is no different in strength from the other channels, ie about 50% to 60%, which is how it has been for a long time. If after 21March things don't get better I'm going to have to go for satellite.

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Nick Flowers's 3 posts GB
A
Adam B
sentiment_satisfiedBronze

5:03 PM
Dunstable

Nick Flowers:

Poor or missing reception when it rains can often means that water is getting into your aerial downlead. It's worth checking that your cable is not damaged, and that it has a good seal where it joins your aerial.

Hope this helps,
Adam.

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Adam B's 91 posts GB
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