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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
Thursday, 15 September 2011
N
Niven
1:56 AM

Hi, I wonder what your opinion is this.

I'm in South Yorkshire on Emley Moor, 17 miles away as the crow flies. The new BBC A Mux that started last week at 174kW shows up as 10/10 strength on my Panasonic TV. The quality shows up as poor at first before going to 10/10 after a second. I'm wondering if I'm going to get too much signal after switchover and whether I should remove my 6-way 4dB amplifier.

I cannot ever re-call having a single problem with all the low power Muxes, including the HD mux, which were all at 75%-90% strength. If the low power signals (4/10kW) came in pretty strong, do you think the new high power ones (174kW) will be overload for my sets? I briefly tried using an 8 way splitter instead, with a 12dB loss, and the new BBC A mux went down to about 8.5/10. I've put the amplifier back for now.

link to this comment
Niven's 11 posts GB
Briantist
sentiment_very_satisfiedOwner

8:41 AM

Niven: You have not provided a full postcode, so it hard to be specific, but yes, it does sound like you have an overload.

As pointed out in the above article, "75%" is a suitable signal strength, it is the signal quality that matters.

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Briantist's 38,846 posts GB
N
Niven
11:18 AM
Sheffield

Ok, S10 5PH.

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Niven's 11 posts GB
Ian Grice
sentiment_satisfiedGold

5:35 PM
Hinckley

What happens if you need the booster as a distribution system?

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Ian Grice's 497 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

5:54 PM

Niven: Purely on the Panasonic issue.

These sets have extremely sensitive tuners, and the symptom you describe of the quality initially showing low then jumping to high is quite commonly seen when the signal they are receiving is on the verges of being a little too strong. (although their tolerance to this is quite good)

This only mentioned in case you thought that it might be a fault.

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jb38's 7,179 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

6:04 PM

Ian Grice: The boosting effect (in reality) of most normal distribution amps is quite low, that is unless one has been chosen that isnt, but if it did exceed what was required and was causing problems on TV's connected into the system, then a simple attenuator in line with its input from the aerial would rectify the problem.

This said provided it wasn't the type of distribution amp that powered a mast head amp or similar, as then an attenuator would be required on each TV that was affected.

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jb38's 7,179 posts GB
M
Mazbar
sentiment_satisfiedGold

7:57 PM
Ormskirk

The main problem with high power transmitters is that it masks any problem you might have with your aerial. If your cable is broken and water is getting in if the transmitter is lower powered the signal would break up when it rains, now with high power transmitters the cable needs to be almost broken to break up, this sound great for customers but when there £1000 tv packs up because water has been pouring into it the high power transmitter is not so good. Winter hill went up from 10 kw to 100 kw they should have increased it to 50 kw this would help most people with problem areas and still show up any aerial problems

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Mazbar's 381 posts GB
Ian
sentiment_satisfiedGold

10:32 PM
Hinckley

I only ask because my signal strength and quality shows almost 100% even before it reaches the amp and is then split 2 ways, one goes to a TV the other goes to another amp and is split 4 ways. Don't seem to have any problems apart from 1 TV that has a quite bad freeview receiver built in that is affected via the power lead. Use the Waltham transmitter postcode LE10 0NS.

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Ian's 497 posts GB
Friday, 16 September 2011
Briantist
sentiment_very_satisfiedOwner

8:29 AM

Ian: It could just be the common problem of a poor quality fly lead on the single set?

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Briantist's 38,846 posts GB
Dave Lindsay
sentiment_very_satisfiedPlatinum

12:05 PM

Ian: Perhaps the pros can clarify whether I'm barking up the right tree here, but what about removing your booster and installing a splitter instead?

Probably best to split it five/six ways if possible and feed each receiver from a single output on the splitter.

Online TV Splitters, Amps & Diplexers sales


Is this a possibility?

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Dave Lindsay's 5,724 posts GB
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