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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, 29 October 2014
J
jb38
sentiment_very_satisfiedPlatinum

4:36 PM

Alan Green: Indications are that Sutton Coldfield is the only station providing good signal coverage in your location. The figures you mentioned of 650 / 642 / and 674 correspond to the multiplex channel numbers of BBC1 / SDN ITV3 etc / and ITV1 respectively, and if you select BBC1 (EPG1) and go into the signal check screen, the Mux channel number should "always" be C43 / 650.00 Mhz, likewise (EPG3) ITV1 being C46 / 674.00Mhz, and with (EPG10) ITV3 being C42 / 642.00Mhz.

Are you using any form of booster? because if your are try bypassing it by connecting the aerial directly into the TV.

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J
jb38
sentiment_very_satisfiedPlatinum

4:52 PM

Alan Green : Further to that said, a Google Earth check on your location would suggest that you "might" be connected into a communal aerial system? should this be the case, then its always the best policy to check with someone else residing in the block just in case the problem is also being experienced by others, as the distribution amplifier that feeds the signals into the individual apartments could have developed a fault.

By the way, it might possibly be of assistance if you provide the model number of the Sharp Aquos TV.

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J
jb38
sentiment_very_satisfiedPlatinum

11:13 PM

Alan Green: Although the problem you are experiencing "is" symptomatic of the TV's tuner reacting to an excessive signal level being fed into the aerial socket, the fact of you stating that it was perfectly OK before the recent retune rather indicates that something other than an excessive signal level is responsible for the problem, at least that is based on the assumption that the company responsible for the maintenance of the communal aerial system did not make any adjustments to distribution amplifiers at the time of the retune.

However, although you may have manually deleted various channels, its really better to carry out a first time installation (or reset) on the TV, as this completely deletes anything stored in the tuners memory including any corrupt data that may have been picked up, but though I cant see a reset facility mentioned in the manual for this model, therefore you will have to resort to the second best.

This involves carrying out an auto tune "but" with the aerial connector having been removed beforehand, as this procedure will (or should) scrub everything in the tuners memory ready for the aerial being reconnected and a normal auto-tune being carried out, although in your particular model, after the aforementioned retune minus the aerial, its best to first of all switch the set completely off (from mains supply) for about 30 seconds or so before powering it up again, then carrying out the initial installation.

By the way, all said is based on your reception being from Sutton Coldfield, which on checking does indicate this being the case, albeit that the local (2,5 miles) Allesley Park transmitter is indicated as being possible to receive but on the basis of being variable, its BBC being on Mux C25, ITV on Mux C22.


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Friday, 31 October 2014
M
MikeB
sentiment_very_satisfiedPlatinum

6:42 PM

Alan Green: Remember that your TV might have just been on the tipping point when you watched it, and being in the middle of the night, there might be a slight difference in atmospheric conditions, hence a slightly lower signal level. Why not use an attenuator (they are just £1.59 each from Amazon), and see if it makes a difference?

Different tuners react in different ways, and they might not have a problem, whereas yours might be a tad sensitive.

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J
jb38
sentiment_very_satisfiedPlatinum

7:03 PM

Alan Green: The frequency of 866.00Mhz would, if it existed, correspond to Ch70, and the fact that your TV is indicating this channel does point to some other factor coming into the equation as the highest frequency used for Freeview transmissions is 786.00Mhz / Ch60.

Purely for test purposes, whilst you are viewing 866 on the signal check screen, remove the TV's aerial plug and connect a short piece of wire (about 2 feet or so) into the socket, as I am curious if 866 is still seen or not, as it might be originating from some source in the block.

Another thing I wondered about is, as your reception would appear to be OK in the early hours of the morning, is 866.00Mhz still being indicated on a signal check screen? or does it only appear at the same times as you are having problems?

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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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Sunday, 2 November 2014
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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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 flag
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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