TV Signal

[DaveOC]

Hi, I have a signal amplifier in my loft which feeds 3 TVs. I have extended one tv point about 3 meters, all works well but every few months or so the picture will start breaking up on 4 or 5 channels Sky news and a few others but never bbc itv C4 etc. after a week or so it goes back to normal. The other 2 TV are unaffected. Anyone got any idea what the problem could be?

 

[Harry Bloomfield]

Hi, I have a signal amplifier in my loft which feeds 3 TVs. I have extended one tv point about 3 meters, all works well but every few months or so the picture will start breaking up on 4 or 5 channels Sky news and a few others but never bbc itv C4 etc. after a week or so it goes back to normal. The other 2 TV are unaffected. Anyone got any idea what the problem could be?

Lucid will be along in a few moments, but in the meantime....

You have a too weak signal to that one TV. You said amplifier, is it just an amplifier, or is it a distribution amplifier, with separate outlets for each cable for each TV?

 

[DaveOC]

It's a distribution amplifier, with separate outlets for each cable for each TV. Could the weak signal be because of a cheap aerial cable(brought from argos)

 

[Lucid]

It's a distribution amplifier, with separate outlets for each cable for each TV. Could the weak signal be because of a cheap aerial cable(brought from argos)

Yep; and @Harry Bloomfield is correct. The signal is too weak on that TV. But it highlights an underlying issue with your aerial system in general.

If the Argos-supplied kit is pulling down the signal enough that you're losing reception occasionally, then it could be a symptom of a weak signal from the aerial system before it even gets to the extension kit. Replacing the cabling with some Webro WF100 / Triax TX100 / Labgear PF100 / Nexans NX100 (basically these are all copper-core, copper shielded cables) will reduce the signal losses. However, you might want to et the aerial checked out or even changed.

The UK has been through a lot of rejigging of the Freeview transmission frequencies. When they've finally finished with us, we'll have lost almost 40% of the available channel space. The upper 2/5ths of the frequency bands will be gone, and so many homes where a wideband high-gain (WBHG) aerial was fitted will find that their reception strength and quality will be much lower since those aerials worked best at the frequencies that we'll have no longer.

For folk in very strong signal areas, where the WBHG aerial is well aligned and there's good line of sight to the transmitter, they'll be okay. There'll still be enough that there's some safety margin left in the signal to stand a bit of additional loss. But for anyone on your position, where adding a kit causes temporary loss, that tells me that the general signal level is already marginal.

I'm a bit short of time at the moment otherwise I'd talk a little about matching the aerial to the transmitter, and the effect of bad cable (generic RG-6 with copper coated steel core and aluminium braid).

As a stop-gap solution replace the Argos kit with some decent coax. If that doesn't completely resolve the issue then either tell us your local transmitter, or put your details in to the What transmitter do I receive a signal from? | Freeview web finder then post the answer back here.

 

[Harry Bloomfield]

Could the weak signal be because of a cheap aerial cable(brought from argos)

As Lucid suggested - yes, that might well be the cause of your issue with that one TV. Your first step should be one of replacing that with some decent quaility cable and plugs.

I bought a similar poor quality 3m extension a couple of months ago, to enable me to move one of our TV's. The TV had worked fine before the extension was tried, but with it in use I began to loose channels. A decent lead cured it.

 

[ericmark]

Isotropic propagation is the technical name. Each broadcast on the mast is at a different height, if you look at smoke from any chimney some times you will see the smoke goes up so far then spreads out, this is where cold and hot air meet, and this causes a channel which radio signals can follow, the CB guys call it skip, so a radio under this layer sends a signal up to the layer then follows the layer for maybe 100's of miles then comes back down, so the range is much extended.

However a radio transmitting above this layer hits the layer and is reflected up, so it does not get to the receiver.

In the North we don't seem to get it that much, but in Suffolk when it happens any signals on a mast under the layer go further, and those over the layer are lost, often you will also get Dutch TV at the same time, pre digital sound and vision had a different split to UK so you would either get sound or picture not both.

As a radio ham we love isotropic propagation, it means we can get much further, but for TV it is a pain.

 

[DaveOC]

Thanks all, I'll try and change the cable unfortunately some of it is buried in the wall, I've attached my local transmitter details if that helps.

 

[Harry Bloomfield]

Thanks all, I'll try and change the cable unfortunately some of it is buried in the wall, I've attached my local transmitter details if that helps.

As s temporary test, leave it buried in the wall, when you try a decent replacement.

 

[Sureitsoff?]

could you tell us the town/village you live in so that we can work out if the small sudbury or larger main transmitters would be better to get your signal from

 

[DaveOC]

Close to Long Melford

 

[Sureitsoff?]

as sudbury is a powerful tx it probably is the cheap lead. how old is the aerial and is it pointing in the right direction just in case the ok tvs have very sensitive tuners and the iffy one hasnt

https://www.aerialsandtv.com/knowledge/transmitters/sudbury-transmitter

 

[Lucid]

The channels you've mentioned having thmrouble with are on mux channel 31 - ARQ A. The last full list I had was:
19 Dave
29 4Music
11 Pick
38 Quest Red
41 Food Network
43 Gems TV
45 Film4+1
46 Challenge
47 4seven
56 Smithsonian Channel
75 Yesterday+1
76 QUEST+1
85 Hochanda
87 Together TV

If this is aerial related then I wouldn't be too surprised if you're struggling too with those on mux channel 29 - SDN:
12 QUEST
16 QVC
20 Drama
21 5 USA
23 CCXTV
26 ITVBe
27 ITV2 +1
30 5STAR
31 Paramount Network
40 Sony Movies Action
44 Channel 5+1
49 TJC
54 5SELECT
58 ITV3+1
59 ITV4+1
63 Blaze
66 CBS Reality
70 Horror Channel
77 TCC
80 Blaze+1
95 Create & Craft
97 ITVBe+1
203 CITV
211 Ketchup
212 YAAAS!

Both 29 and 31 are towards the bottom of the channel range for Wideband High-Gain aerial, so the signal level coming off it at the lower frequencies will be weaker. Combine that withbtge effect of the extra losses from a poor coax extension...

Another possibility is some damage such as crushing or a sharp bend in some coax causing a frequency specific signal loss. Its almost as if the the cable kink acts like a notch filter.

It's worth though checking out some of the simpler stuff first. Remake any coax plug connections. Make sure there good contact for the centre pin and no stray filaments of shielding braid touching the centre pin.

 

[ericmark]

I wish my freeview had so many channels. But are neighbours having same problem. In north and mid Wales we don't get Skip much, when I lived is Suffolk it was common. You don't want to do loads of work if down to weather conditions.

 

[DaveOC]

I remember the guy that fitted the aerial said the signal was too strong and had to point the aerial slightly away from the transmitter which I can see from my roof, not sure if this was right but it's be up for about 15 years.

 

[Lucid]

I remember the guy that fitted the aerial said the signal was too strong and had to point the aerial slightly away from the transmitter which I can see from my roof, not sure if this was right but it's be up for about 15 years.

At 9 miles(?) from a 100,000W transmitter I wouldn't be too surprised at that. However, at the time, pre DSO, all your channels were at the upper end of the frequency range. They were from RF ch39 to RF ch68. That would be a really good fit for using a Wideband High-Gain aerial (WBHG).

The correct method when signal is too strong is to use an attenuator somewhere near the TV. Should the situation with reception ever have changed, then this could be reduced or removed completely. By turning the aerial away from Sudbury he had bodged a solution but then created future problems.

First, it reduced the reception power throughout the whole of the aerial's signal range. This includes the lower part of the range where the aerial doesn't work as efficiently. Since the aerial doesn't pull in as much signal at the lower end of the range compared to the upper end, the effect of that reduction is much more pronounced with the lower RF channels. It's a maths thing. Say I gave two people some money, one getting £100 and another getting £20. Then ask them each to donate £10 to my favourite charity, the guy with £100 'lost' 10%, but the guy with £20 lost 50%. That's what happened when your installer turned the aerial. He made a reduction to the "£100 guy" (the upper mux frequencies), but the same reduction was felt more savagely by the £20 guy.

Second, being off axis means that there's a potential that the aerial is now pointing more towards some remote transmitter that it wouldn't normally see if correctly aligned. Do you remember @ericmark's point about isotropic propagation? That's when the atmospheric conditions are just right that a signal from a far distant transmitter bounces of the underside of an atmospheric layer. It's like having a mirror so you can see around a corner.

Third, the transmission frequencies have shifted from Sudbury. They're now in the range from 29 to 47. They're in the weak zone for a WBHG aerial. In fact, the channels where you notice a problem are at the lowest and weakest end of a WBHG aerials reception range; your Sudbury ARQ A on RF ch31. That, plus the aerial's reception being made weaker by being off axis, makes RF ch31 disproportionately weaker than the higher RF channels.

Add to that 15 years of wear and tear a on the aerial, and on the cabling, the chance that the aerial may have moved further over time, and maybe there's tree growth to consider, or perhaps new buildings changing the line of sight signal conditions.

Then there's the nature of the signals for digital TV. It's different from analogue. With that, a progressively worsening signal would get snowy until it reached a point where finally the signal was lost. Digital is more like a light switch. As long as the signal is over a minimum threshold, then the reception looks just as good as if you've got the maximum signal. However, that difference between minimum and maximum gives you your fault tolerance for reception issues. The closer the signal is to the minimum, then the more likely that the switch gets flipped to Off if the reception conditions aren't right. That's pretty much what you're experiencing now.

It looks from what you've said that you have a perfect storm of conditions to create the problem: the aerial is no longer the best match, the installation is compromised to further reduce the signal, 15 years of wear and tear, minimal fault tolerance, then some atmospheric condition that means a remote transmitter bleeds its signal over your local transmitter's frequencies.


The solution here is to get a better matched aerial installed, correctly aligned, to give proper signal level at the TV points - 50-55dBuV as a level is about the range, though TVs will work quite happily with 60-65dBuV in my experience. Any signal-level attenuation should be fitted in-line at the back of each TV. This way is can be increased/reduced/removed by you rather than calling out an installer if situations ever change in the future. While you're at it, have the aerial downlead in to the loft replaced with Webro WF100 if it's not already that cable.

I can't rule out the possibility of further isotropic interruptions, but if you give the aerial system its best fighting chance, then you reduce the chances of it happening.