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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
Saturday, 1 November 2014
J
jb38
sentiment_very_satisfiedPlatinum

12:17 AM

Alan Green: Sorry for the slight delay in replying. However, on having had another look at the manual for your model, and in particular the additional search menu which you refer to, as this section is really intended for searching for additional channels "after" an auto search has been completed, I really don't feel that venturing into this area is going to assist in any way with alleviating your problem, therefore you should revert to carrying out an auto-tune "minus the aerial being connected" then on completion, reconnect the aerial and carry out a second auto-tune to reload the programme EPG numbers into the tuners memory.

The main point being, that the fact of you having reported that the problem does not seemingly exist when viewing is carried out in the early hours of the morning, strongly suggesting that the problem is "not" being caused in any way by anything you have done, but by factors elsewhere.

That said though, it wouldn't do any harm to purchase one of those attenuators referred to by MikeB purely for the purpose of determining if a slightly over the top signal is the cause of the problem, although I do have to say that I very much doubt if it is, as I cant quite see how anything could have changed from what it previously was when nothing has changed power wise on the transmitters

I do have another line of thought, and being, that an element of the coincidental is involved in the timing of the problem having started, and that it could be caused by someone located in an adjoining apartment (inc above or under) having started to use (during daytime hours) some device such as an Ethernet mains power line adaptor etc, as these devices have a reputation for causing interference to a range of RF receiving devices including DTT, the fact of your reception being OK in the early hours of the morning possibly coinciding with the device having been switched off during bed time hours.

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jb38's 7,179 posts GB
Sunday, 2 November 2014
A
Alan Green
1:07 AM
Coventry

HI JB38,
i have tried everything you have suggested and nothing has changed.The cable connected from the back of the TV to wall socket is about 2 feet long and the connection to the wall i have a coax-female,female- coupler,do you think it would make any difference if i changed it to a better one. and if so is it a aerial attenuator i need to replace it with.I went online and there seems to be 2 types.the first is 6dB and the second a 12dB can you tell me which one would be the correct one to get if you think this would help.

Though i have tried everything,I am coming to the conclusion it is the frequency 866.0 Mhz that is causing these problems because when i go on channel 66 0r 68 it seems worse and i think i should not of went into manual search to scan the channels because i know that this frequency was 866.0 Mhz beforehand and it seems set now and i will not be able to undo this.As for the EPG you mentioned when i press the EPG button the tiles that show all the programmes in that section takes between 20 & 30 seconds before all the tiles fill in.

KIND REGARDS
ALAN GREEN

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Alan Green's 9 posts GB
A
Alan Green
1:11 AM
Coventry

JB38,
i meant to say that the 866.0 Mhz was not as high as it was before i done manual search for channels as it was much lower.

KINDS REGARDS
ALAN GREEN

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Alan Green's 9 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

2:37 PM

Alan Green: On the subject of the attenuator, although the actual true level of the signal (as on proper dB meter) is not known, but if its only slightly over the top then the 6dB version of the attenuator should be sufficient to take the edge off it, although I do have to emphasise that an element of hit and miss exists about anything suggested, as I am not entirely convinced that your problem is being caused by the signal level being excessively high, basically due to you being connected into a communal system where the output levels are pre set by the installers of the distribution amplifiers, but though one never knows!

As far as 866.00Mhz is concerned, as was previously mentioned, nothing (to my knowledge anyway) transmits on that frequency, that is "if" a transmission is actually taking place on that frequency, and your not just picking up the 1st harmonic from a 70CM beacon used by radio amateurs, should such a thing be located nearby, and it would have to be nearby! Although I am a bit out of touch now with what goes on in that band.

Anyway, I feel that your best policy is to revert back to square one by carrying out an auto tune "after" having removed the aerial connector beforehand, this action blanking out anything stored in the tuners memory, reconnecting the aerial again when the scan has completed then selecting "auto installation" (Menu > Set up > View setting > Auto installation).

By the way, do you have the manual for your TV? and if you do, is your page 37 headed "basic settings"?. My only reason for asking being, that it would enable me to refer to a page in the manual (or section within) appropriate to the subject of the discussion.

Another point I am not sure about is, when you found that your reception was perfectly OK in the early hours of the morning, is this always the case? at least any time that you have managed to try it?

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jb38's 7,179 posts GB
A
Alan Green
3:54 PM
Coventry

Hi JB38,
After my last post i watched the TV in the early hours of the morning and i went through every channel and the problems i have been experiencing did not occur, every single channel that i checked the signal was on the signal bar was on the max 99 and the quality bar was on the max99 also.If this is the case then you must be correct that either there is something in the block or from elseware that is affecting the frequency so i will just have to hope that the problem rectifies itself over time but would like to say thank you for your help in this matter and wish you the best.

KIND REGARDS
ALAN GREEN

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Alan Green's 9 posts GB
M
MikeB
sentiment_very_satisfiedPlatinum

4:35 PM

Alan Green: If your signal level was on 99 at that time in the morning, it could well be that during the rest of the day (for whatever reason), its breaking up because its too powerful. I entirely agree with JB38, start with the basics, because by the time everything has been fiddled with, a seemingly simple problem can become a complex one!

There are no 'correct' attenuators. I bought a number of different ones, from about 6 upwards. Another flylead connects the output of one to the TV. etc. Try the weakest one first. If it brings the signal strength down a bit and there are no further problems, then great. If it doesn't, try the next one and so on. If you need a stronger attentuator, you can put them in series, so a 3 and a 6 become 9, for instance.

Frankly, I dont think the problem is going to magically diappear - signal strength is not going to decrease in the future, and for about a fiver, you can at least eliminate one potential cause.

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MikeB's 2,579 posts GB
J
jb38
sentiment_very_satisfiedPlatinum

5:31 PM

Alan Green: My suspicions about the interference possibly being from elsewhere, such as a device installed in one of the adjoining apartments, was when thinking about a problem another viewer had experienced with his main living room TV a number of months ago, the problem being constant interference on a number of channels which made viewing them nearly impossible, and yet the the reception was OK on the TV's installed in the rest of the house, numerous people on this site having offered suggestions as to possible causes, including in the latter stages myself.

Anyway, after the viewer had went to a considerable amount of bother trying to re route cables etc it was found out that the interference rapidly diminished when the TV was pulled away from the wall, the problem transpiring as being caused by a Virgin Media cable box installed in the adjoining property, the offending VM box being located on the other side of the wall from where the viewers TV was installed, hence why the interference diminished when the TV was pulled away from the wall, some digital devices causing intense interference if only a few feet away from them.

The other main point being, that similar to what you experience when viewing during the early hours, this viewer noticed that the interference ceased at certain times, usually when those involved were on holiday.

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M
MikeB
sentiment_very_satisfiedPlatinum

5:51 PM

jb38: Good point, I'd forgotten about that. Perhaps a better (shielded) flylead might help?

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MikeB's 2,579 posts GB
Monday, 3 November 2014
J
jb38
sentiment_very_satisfiedPlatinum

12:58 AM

Alan Green: With reference to that said in my previous posting regarding a problem that had plagued another viewer, there is a relatively simple test that you can carry out "if" you possess a portable radio capable of receiving long wave transmissions, i.e: Radio4 long wave 198Khz.

Receivers capable of receiving long wave transmissions are ideal for detecting interference from a variety of devices in the home, and although usually always associated with noisy switching systems such as water tank thermostats or central heating switches etc, digital devices emitting high levels of radiation capable of interfering with reception can also be detected.

The procedure involves tuning the radio to just off Radio 4 long wave198Khz until only a mush is heard through the speaker, then advancing the volume.

The next stage is to completely switch off your TV or any other digital device positioned nearby to it, then sweep the area with the radio from behind your TV along to where the wall socket is located, should any high levels of digital interference exist it will be revealed by a loud buzzing being heard on the radio, although some devices emit a high pitched whining noise.

Needless to say, this test should be carried out in two stages, the first with the TV switched off whilst the reception problem is known to exist, the second being repeated (whilst the TV is switched off) but this time during the early hours whilst the reception is known to be OK, the TV only being switched off in both cases simply to eliminate the detection of your own TV.

The test is a bit crude, but it does serve a purpose by indicating if anything changes between day and night time hours.

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jb38's 7,179 posts GB
Tuesday, 4 November 2014
A
ALAN GREEN
1:00 PM
Coventry

Hi MikeB:
The signal bar as always been on the max 99 its the quality bar that is not on the max as it bounces up and down from 0 -1,14 26, 64, and back to 0but from 10pm onwards the signal bar is on the max 99 and so is the quality bar and the tv is fine,Its during the day time it is at its worse.I have asked the neighbours but they are not having these problems.Can you explain what a better shielded flylead means and how would i know the difference and what does this do also do i need to ask for a shielded flylead if decided to buy one.

KIND REGARDS
ALAN GREEN

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