Tv signal issue

[Jonboy]

So I live in a ground floor flat and normally rely on the communal Aerial on a passive basis.

 

Since the recent retuned the Oxford transmitter I have found that I can:

 

only receive the bbc cohort of channels with an signal amplifier in the loop connected to an indoor aerial.

 

only receive channel 4/itv cohort, without the signal amplifier in the loop, from the communal aerial.

 

Cannot receive Dave/pick etc at all (but can get enough of the signal for the tv to tune them epg etc).

 

Our neighbours don’t have an issues....I don’t have another tv or freeview box to test with.

 

Any thoughts to the likely cause as the flipping between the two aeriels is annoying.

[Jonboy]

Ohhh and I have changed the lead from wall to tv as part of my testing.

[Nearholmer]

High impedance in your branch of the aerial connection?

 

Could be a connector that is visible to you, or something further back that isn’t.

 

If the returning of the transmitter either reduced signal strength, or moved things to new frequencies, that might be enough to reveal a problem that was invisible previously.

[mezzoman253]

It may be due to the antenna being unsuitable for the new frequencies the Muxes are on.

 

Here I watch TV from the Crystal Palace transmitter and have lost several channels due to my recently installed replacement antenna being band "A" and the channels being moved to band "K". 

 

There's more of these changes in the pipeline, so be prepared to lose, or gain, channels. 

 

All to do with releasing more frequencies for mobile 5G, and the resultant megabucks for the government.

 

Rob

[ejstubbs]

It may be due to the antenna being unsuitable for the new frequencies the Muxes are on.

 

You would expect that to affect the other users of the communal aerial as well, though.  The OP says they don't have issues.

Edited July 6, 2018 by ejstubbs

[34theletterbetweenB&D]

How critical are the other users though? One person's 'no problems' can be another's 'completely unacceptable'.

 

If it is practical to tote the receiving equipment to another flat and try it there, more truth may be revealed. Did a little of this locally after the last 'big retune' in our area and it was the (some years old) receiving kit of the newly dissatisified couple that was the trouble, rather than a poor signal from their fairly recently replaced aerial.

 

If the signal is degraded, then as it is a communal aerial and feed to the flats, how is it maintained? If it is covered by a maintenance charge then whatever entity manages that should be put on the case, even if it is only one occupant affected.

[ejstubbs]

Actually, having checked what changed on the Oxford transmitter, I'll admit that it does look like an aerial issue could be at the root of the OP's problems.  On 23rd May the muxes were re-allocated from the UHF channel range that requires a group C/D aerial (channels 48-68) to a range that requires a group T aerial (channels 21-60).  The multiplexes that the OP reports problems with used the following UHF channels before, and then after, that changeover:

 

BBCA (most BBC channels) - was channel 53+, now channel 41

D3&4 (ITV and Channel 4) - was channel 60-, now channel 44

Arqiva A (Dave & Pick) - was channel 59-. now channel 37

 

That means that all of the above multiplexes are 'out of group' for a group C/D aerial.  However, a grouped aerial doesn't cut off out-of-group UHF channels completely, it just has significantly poorer gain for out-of-group channels the further away you get from the boundaries of the group.  Hence (probably) why mux D3&4, which is only 4 channels outside the C/D group, is receivable through the communal aerial by using a signal amplifier, but the others are not.

 

BBCA being receivable on an indoor aerial is almost certainly because the indoor aerial is wideband ie it covers all the UHF channels (currently) allocated to terrestrial TV (AFAIK all indoor aerials are wideband, you can't get grouped ones).  In that case the signal amplifier would be required simply because the signal received on the indoor aerial would be weaker because it is, er...indoors - as well as being smaller, and generally never likely to perform as well as a rooftop aerial.

 

As for ARQA, as well as being well out-of-group for the communal aerial, AFAICS it is broadcast at half the power that the BBCA and D3&4 multiplexes are broadcast at, hence (probably) why it cannot even be received on the indoor aerial.

 

My conclusion based purely on the symptoms reported by the OP would therefore be that the communal aerial is now in the wrong group for the retuned Oxford transmitter.  Whoever is responsible for the communal aerial may need to swap it for a group T aerial.  (Ironically it would probably be the BBCB multiplex, that carries the HD channels, that would be received best on a group C/D aerial post the Oxford retune, since it's ended up only one channel outside the C/D group!)

 

However, that still leaves a bit of a mystery as to why the OP's neighbours don't have the same problem.  It rather suggests that they might actually be using a different aerial to the OP (maybe there are in fact two 'communal' aerials in the same property?)  Or maybe they are using satellite, or broadband TV!

 

How critical are the other users though? One person's 'no problems' can be another's 'completely unacceptable'.

 

Digital TV, like digital radio, tends to be either there or not (sometimes referred to as the "digital cliff").  It's not like analogue TV whereby the picture might be fuzzy, or have ghosting, but at least it was a picture...

Edited July 6, 2018 by ejstubbs

[Nearholmer]

It was as that sort of thinking that led me to suggest a problem with the OP’s branch ........ the signals may now be weak, but not critically weak except on his branch.

[34theletterbetweenB&D]

...

Digital TV, like digital radio, tends to be either there or not (sometimes referred to as the "digital cliff").  It's not like analogue TV whereby the picture might be fuzzy, or have ghosting, but at least it was a picture...

 The effect is different from analogue, true enough, but the end result can be the same if others are only using a few channels in a mux from which reception is still adequate, as far as they are concerned 'it works', but channels on another mux may well be unavailable. But as non-users they are completely unaware.

[Jonboy]

Thanks for the suggestions everyone, I think the idea of trying the tv in a neighbours flat is a great one and will get on this over the weekend.

 

 

I will then get onto the block managers on Monday and see if their records show the type of aerial fitted.

[ejstubbs]

I will then get onto the block managers on Monday and see if their records show the type of aerial fitted.

 

If they don't know then ask them to look at the aerial: the colour of the end plug indicate the aerial group.  See http://www.digitaluk.co.uk/reception_guide.  Group C/D is green, group T is white.

 

I note that on this page they say:

 

"Aerial changes are most likely to be needed where TV services are broadcast in the aerial group C/D, which uses the 700MHz frequency band. However, most homes using C/D aerials should continue to receive reliable signals after clearance."  (My emphasis.)

 

I think it's pretty clear that that was unlikely to be the case for Oxford, where every multiplex except COM6 used a UHF channel in the 700MHz band.  Given that, I would have thought that someone, somewhere should have put a special effort in to informing the local populace of the issues they might face.

Edited July 6, 2018 by ejstubbs

[mezzoman253]

If they don't know then ask them to look at the aerial: the colour of the end plug indicate the aerial group.  See http://www.digitaluk.co.uk/reception_guide.  Group C/D is green, group T is white.

 

I note that on this page they say:

 

"Aerial changes are most likely to be needed where TV services are broadcast in the aerial group C/D, which uses the 700MHz frequency band. However, most homes using C/D aerials should continue to receive reliable signals after clearance."  (My emphasis.)

 

I think it's pretty clear that that was unlikely to be the case for Oxford, where every multiplex except COM6 used a UHF channel in the 700MHz band.  Given that, I would have thought that someone, somewhere should have put a special effort in to informing the local populace of the issues they might face.

Yes, letting the public know wasn't well done here either. I'd not long put up a replacement for our venerable outside antenna. The new one is in the loft but gives good reception, we are line of sight with Crystal Palace and there's some headroom in the gain figure.

 

So imagine my surprise after re-tuning that some new channels we'd had for about 6 months, Freesport, AFN, etc, all disappeared. When I looked at the frequencies involved I realised that the new antennas' gain tapered off at about the point these frequencies had been moved to, and I now need a different band model to cover everything.

 

Had I known these changes were due I'd have got a suitable antenna beforehand. Now I've got to do it all again. 

 

At least I don't have to get on the roof though.

 

Rob

Edited July 6, 2018 by mezzoman253