Full Freeview on the Mendip (Somerset, England) transmitter
 | Google Streetview |  | Google map |  | Bing map |  | Google Earth |  | 51.237,-2.626 or 51°14'12"N 2°37'33"W |  | BA5 3LB |
The symbol shows the location of the Mendip (Somerset, England) transmitter which serves 720,000 homes. The bright green areas shown where the signal from this transmitter is strong, dark green areas are poorer signals. Those parts shown in yellow may have interference on the same frequency from other masts.
Are there any planned engineering works or unexpected transmitter faults on the Mendip (Somerset, England) mast?
Mendip transmitter - Mendip transmitter: Possible effect on TV reception week commencing 04/11/2024 Pixelation or flickering on some or all channels 
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Digital television services are broadcast on a multiplexes (or Mux) where many stations occupy a single broadcast frequency, as shown below.
64QAM 8K 3/4 27.1Mb/s DVB-T MPEG2
DTG-12 QSPK 8K 3/4 8.0Mb/s DVB-T MPEG2
H/V: aerial position (horizontal or vertical)
Which Freeview channels does the Mendip transmitter broadcast?
If you have any kind of Freeview fault, follow this Freeview reset procedure first.Digital television services are broadcast on a multiplexes (or Mux) where many stations occupy a single broadcast frequency, as shown below.
64QAM 8K 3/4 27.1Mb/s DVB-T MPEG2
DTG-12 QSPK 8K 3/4 8.0Mb/s DVB-T MPEG2
H/V: aerial position (horizontal or vertical)
Which BBC and ITV regional news can I watch from the Mendip transmitter?
ITV West Country News (East) 0.9m homes 3.4%
from Bristol BS4 3HG, 23km north (11°)
to ITV West region - 61 masts.
All of lunch, weekend and 50% evening news is shared with West Country (West)
Are there any self-help relays?
| Cheddar | Transposer | 15 km E Weston-super-Mare | 1674 homes |
| Luccombe | Active deflector | 6 km w Minehead | 38 homes |
How will the Mendip (Somerset, England) transmission frequencies change over time?
| 1984-97 | 1997-98 | 1998-2010 | 2010-13 | 2013-18 | 2013-17 | 27 Feb 2018 | |||
| C/D E | E | E | C/D E | C/D E T | W T | W T | |||
| C30 | _local | ||||||||
| C32 | BBCA | ||||||||
| C33 | com7 | com7 | |||||||
| C34 | D3+4 | ||||||||
| C35 | com8 | com8 | |||||||
| C36 | ArqB | ||||||||
| C37 | C5waves | C5waves | |||||||
| C48 | SDN | SDN | SDN | SDN | |||||
| C49tv_off | BBCA | BBCA | |||||||
| C51tv_off | LBS | LBS | |||||||
| C52tv_off | ArqB | ArqB | ArqB | ||||||
| C54tv_off | C4waves | C4waves | C4waves | D3+4 | D3+4 | D3+4 | |||
| C55tv_off | com7tv_off | ||||||||
| C56tv_off | ArqA | ArqA | ArqA | COM8tv_off | |||||
| C58tv_off | BBC1waves | BBC1waves | BBC1waves | BBCB | BBCB | BBCB | |||
| C61 | ITVwaves | ITVwaves | ITVwaves | BBCA | |||||
| C64 | BBC2waves | BBC2waves | BBC2waves |
tv_off Being removed from Freeview (for 5G use) after November 2020 / June 2022 - more
Table shows multiplexes names see this article;
green background for transmission frequencies
Notes: + and - denote 166kHz offset; aerial group are shown as A B C/D E K W T
waves denotes analogue; digital switchover was 24 Mar 10 and 7 Apr 10.
How do the old analogue and currrent digital signal levels compare?
| Analogue 1-4 | 500kW | |
| Analogue 5 | (-6dB) 126kW | |
| SDN, ARQA, ARQB, BBCA, D3+4, BBCB | (-7dB) 100kW | |
| com7 | (-8.4dB) 72.4kW | |
| com8 | (-8.6dB) 69.1kW | |
| Mux 1*, Mux 2*, Mux A*, Mux B*, Mux C*, Mux D*, LBS | (-17dB) 10kW |
Which companies have run the Channel 3 services in the Mendip transmitter area
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Thursday, 5 November 2020
C
Chris.SE6:04 AM
Alan_C:
Hmm, I understand about the long waits on the phone for that free help back then. Freeview have not (IMHO) been well organised or manned to cope with those for quite a few of the transmitter changes around the country. It is worth being clear though that the changes are as a result of Europe wide changes and agreements, it's not just this country "selling off bandwidth".
Which make and exact model of aerial did you get?
In relation the mux at the "edge of the band", it would be helpful if you could be specific as this could be the top (I suspect you mean COM7 on C55) or possibly the bottom of the band (Local mux on C30).
Your remarks about signal strength and quality do make sense as it is possible to have too much signal which can result in a set's strength figure readings appearing to be lower and certainly the quality figures will drop in those circumstances, BUT equally a failing amp could do similar things. It is also helpful to compare the figures with the other muxes at the same time.
Does you TV not have strength and quality information somewhere in it's tuning section, maybe in manual tuning? Most sets have it somewhere.
To be able to make some sensible comment and suggestions, we really need a full postcode to see what the Freeview Detailed Coverage Checker gives for your predicted reception and the aerial bearing for the transmitter at your location.
We also really need to see the Strength and Quality figures for each multiplex with the aerial direct to the TV without any splitters or amplifiers. Then the same again with the amplifier.
As far as recovering lost muxes and channels, this 4th.Nov. retune has given some other people problems and it's not been/going to be helped by the fact that there's some predicted "Tropospheric Ducting" around with the current high pressure which may result in interference from distant transmitters to some of the multiplexes at varying times! (see Effect of tropospheric ducting on Freeview | RTIS for a simplistic explanation).
The best way to try and recover everything correctly is to try retuning in the following way -
First unplug the aerial and do an automatic retune - this should clear all previous tuning as no channels should be found. (This technique doesn't always work on some devices and a factory reset might be required).
Once previous tuning is cleared and no channels present then plug the aerial back in direct to the TV (no amp or splitters) and ideally do a manual tune for Mendip's UHF channels which are C32, C34, C35, C48, C33, C36, C55, C30 and that's in the order PSBs1-3, COMs4-7 and the Local mux.
If manual tuning isn't possible then it'd have to be an automatic one.
If you post back with as much of that information as possible, we should be able to help further.
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Saturday, 7 November 2020
A
Alan_C6:01 PM
Somerton
Chris.SE:
Many thanks for you comprehensive and helpful response.
In answer to your questions and comments:
Aerial is XB10K from ATV, mounted in the loft (using the cradle and a short pole down from the rafters).
The channels I lost were on the mux COM4 at channel 48, so actually not the highest frequency - I regret I don't know whether I also lost channel 55 (or indeed whether I even had it before the retune).
Prior to the PVR box filing I was using the signal strength indications on that, but I have found you are right that signal strength is available in a manual tune of the set.
Postcode: TA11 6SH.
I followed your recommended procedure today (Sat) now that the pressure has dropped (automatic retune with aerial disconnected, then reconnect (without splitter) and manual retune one channel at a time. Here are the strengths and qualities for each:
32 Q 100 L 65
34 Q 100 L 65
35 Q 100 L 55
48 Q 20 L 50
33 Q 100 L 60
36 Q 100 L 60
55 Q 0 L 0
30 Q 0 L 0
I viewed one channel briefly from each frequency channel (if you see what I mean) and they were all good (but of course I don't have any channels from 30 or 55).
So that's fantastic and thanks. Do you have any recommendations about 55 and 30?
Alan
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Alan_C's: mapA's Freeview map terrainA's terrain plot wavesA's frequency data A's Freeview Detailed Coverage
A
Alan_C6:28 PM
Chris:
Oh, and I meant to say that although the one channels (Drama) that I've watched so far on frequency channel 48 is watchable, there is intermittent pixellation. I'd be grateful for any suggestions about improving the signal for this channel, which came up with Quality 20% and Level (signal strength) 50% .
Thanks again,
Alan
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Sunday, 8 November 2020
C
Chris.SE4:06 AM
Alan_C:
I assume those figures are without the amp. Can you put the amp in and see how the figures compare without changing anything else.
That quality and signal strength on C48 is of concern. The SDN/COM4 mux is the only one that hasn't moved UHF channel at sometime or other!
That XB10K is a good aerial and on paper the gain at C55, C48 & C35 should be pretty much identical.
The Freeview predictor say all the main muxes should be blowing your windows out, but being in a loft will attenuate things. Without an amp, and lower transmission power for C55, that may make a significant difference. The Local mux on C30 is the exception for which you may get nothing as it's beamed N towards Bristol.
Your aerial should be pointing at a bearing of 22 degrees (NNE) but may need tweaking because of its location in the loft.
To address this C48 performance. Lots of things to check.
Have you got anything with an RF modulator running which might be causing interference eg. RF output from a VCR or other devices, Games consoles and the like. If so change the channel to 60 or above if possible.
Check you have no breaks or kinks in your downlead or any flyleads you may be using. Pre-made flyleads are often a problem with breaks at the back of the connector. Check connections on any walls plates for corrosion etc. None of this will necessarily affect all multiplexes as it can cause standing waves to be set up in the cable and what frequencies are affected will depend on cable lengths etc.
Assuming you've not found issues with downlead, flyleads etc, consider position of the aerial in the loft - check its not got any metal objects nearby - flues etc. electric cabling, especially in the direction it's pointing. Similarly partition walls. Also roof flashing, solar panels and the like.
If nothing else has come to light, try altering the bearing slightly and see how it affects the figures.
If that doesn't make much difference try altering it position, move it backwards, forwards, sideways etc.
Post back the figures with the amp in circuit first, that may be quite revealing.
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C
Chris.SE5:34 AM
Alan_C:
Almost forgot, do you have anything connected with HDMI? Keep the leads well away from aerial and flyleads, as they can cause interference especially to C55.
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A
Alan_C2:53 PM
Chris.SE:
Chris:
Figures with amp connected (Commtel 4 channel amp/distribution device) in the loft, connected between the aerial lead and the cable running down to the wall plate, built in to the wall):
32 Q 60 L 100
34 Q 65 L 100
35 Q 0 L 100
48 Q 55 L 100
33 Q 30 L 100
36 Q 35 L 100
55 Q 0 L 95
30 Q 0 L 0
Note the increase in signal level across the band (including ch55); but also note the loss of quality across the band, with the exception of ch48 which benefits.
I know the Freeview map shows good coverage in my locality but the truth is there are many pockets in Somerton where people are slightly lower down and do not get good signals. Our installation situated on the plateau doesn't have unobstructed LOS to Mendip. It is also notable that about 50% of the properties around have two aerials - the other being directed to Stockland Hill. While this could be because they identify with SW rather than W region, it also apparent that we're about halfway between the two transmitters - and the direction to Stockland isn't far from -180 degree endfire on my aerial (I wonder what its reception pattern is like out of the back?). And I would add we get very poor FM radio even with a separate dedicated outdoor antenna, and no usable DAB. But that's off topic except that it does indicate we're not so well served by Mendip.
Thanks for the suggestions re. VCR, etc. We do have a VCR connected using SCART - I'd forgotten about the RF modulators in these things. Switching off the VCR and a DVD player, and removing an HDMI lead, made no difference to the signal / quality measures.
Interesting thought about standing waves in the cables. I've checked and swapped around all leads; also tried a long cable from the loft instead of the installed cable and wall plate. No changes seen.
The position in the loft is rather constrained, it needs to point through the gable end rather than the tiles because we have solar PV, and there aren't many places with enough headroom. The DC cable for the solar panels does run perpendicular to the aerial axis, close to the pole.
I'll wait for any further thoughts and comments before attempting to realign the aerial or move it sideways., as without any kind of analogue meter up there with me this is a bit of a trial and error activity. Initial alignment was just based on the required bearing!
Slight change of topic, but are we to expect Com7 to be switched off sometime in 2020?
Again, very grateful for your inputs (were you really typing at 4-5am?!!).
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Monday, 9 November 2020
C
Chris.SE2:27 AM
Alan_C:
It's probably fair to say that none of the coverage maps or predictors are 100% accurate, the less variable the local terrain, the more likely they are to give some believable figures, that said the Freeview Detailed Coverage Checker doesn't show any variation across the 6 main muxes, only COM7 very marginally less reliable for your postcode.
It does also show very good reception from Stockland Hill (bearing 223 degrees) and as it happens some good and variable reception from Wenvoe (bearing 320degrees)! Stcckland Hill is 38km from you, Mendip 22km, Wenvoe 59km.
The aerial is likely to have some moderate side lobes to the rear sides, I'd try just out of curiosity to see what you could pick up without moving the aerial (with the amp connected). Stockland Hill's UHF channels are C26+, C23+, C29+, C25-, C22-, C28- for PSBs1-3, COMs4-6, no COM7 or Local. Don't worry about the +/- offsets, TVs tune quite happily.
Now, well done for trying the long cable, all that you did were useful checks. One query in relation to the amp, when you had the aerial connected directly (first set of figures), was the amp still switched on/powered up? IF so, try the aerial connected direct again with the amp powered off and see if there's any differences (this should make sure that the amp isn't causing any interference).
The set of figures with the amp in circuit are now suggesting too much signal, hence the drop in the quality figures, that's why you found some improvement when you introduced that splitter giving some attenuation as mentioned in your original post. Although this C48 problem is still another issue (eg. it could be aerial position in relation to maybe your solar PVs or other things, if it wasn't a problem with the amp itself which the check I've just mentioned should confirm).
Its also worth considering other possible sources of interference that may be affecting C48 if the amp is eliminated. Try switching off anything that might be running constantly when you've been looking at figures or having problems with reception (not fridges/freezers/central heating as these go on and off) but any lighting running off transformers, fluorescent fittings, compact fluorescents, LEDs, or any other discharge lighting eg.outside. Anything else that has any electronic control that's powered all the time.
As you have a 4-way amp/splitter, I assume you may have at least one other TV elsewhere in the house. Does it show similar relative figures for each UHF channel?
If there doesn't appear to be any problems with the amp, then it would probably a good idea to get one of these eBay item: 310039226920, Coax TV Aerial Attenuator Adjustable Variable Between 0-20 dB Reduces signal | eBay
IF the amp does turn out to be an issue then any replacement might usefully have a variable gain control.
If we've got to the point that everything else that could be causing interference or poor reception has been eliminated, then we are most likely down to aerial position. Whilst absence of a meter might making things somewhat tricky with a bit of trial and error, initially we're only interested in whether reception is being adversely affected by position. Without the amp in circuit, I would initially take it off the pole and remove the pole and just move the aerial sideways and say back away from the solar PVs and just have it sitting on the beams/loft floor doesn't matter if it say overhangs your loft access or whatever, to start with we're just looking for what significant (if any) changes there are in signals.
If you've got a 2nd set and it was showing similar relative figures to your main set, maybe you could position it somewhere nearer the loft which would make any to-ing and fro-ing a bit easier.
If you can post back with the info about whether the amp was on when you did the first figures and any differences if so, and any comparison with a second set, checks on other potential sources of interference etc. I can see if any of that modifies my thoughts.
I replied to your DAB post, yes I was up, had been watching news on the US election then decided to watch a film (sad I know!). COM7 is not likely to close in 2020, it's anticipated that the earliest would be later in 2021 IF any MNOs buy the SDL frequencies when the auction is held scheduled in the new year, they could then give 3 months notice to be able to use the frequencies, but equipment would need to be installed as well as suitable handsets available and this won't happen overnight. That said, Arqiva closed COM8 for commercial reasons primarily due to loss of advertising revenue in the covid-19 situation and broadcasters being uncertain about the future wanting to cut costs, so that might have a future effect on COM7, personally I don't think it's a high probability.
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Tuesday, 10 November 2020
A
Alan_C5:29 PM
Chris.SE:
A quick but partial answer...
I like the idea of seeing what signal I can pick up from Stockland Hill using side lobes, without realigning the aerial - I'll do that at the weekend (don't want to get in the bad books of my wife). That'll also be the best time for me to try some rotation / repositioning of the aerial. And that's probably my best time for switching other things off. Like most people I guess, I have a few things which are "always on", like the wifi router. I don't think there's anything which has been put in fairly recently, though, except central heating (which has all wired thermostats, nothing radio-connected). My neighbour has been doing a lot of work in his house - I hope he hasn't installed anything operating on 690MHz!
Going back to the amplifier; when I tested with the amp disconnected it was moved away from the leads and fully powered down, and the aerial lead and the cable to the wallplate joined using a female-female back to back connector. As you've said, the figures show that the amp does provide gain ;-) which is probably not needed, and causes overloading of the tuner. But they do seem to suggest that the signal out of the aerial on Ch 48 is genuinely quite a bit lower than other channels; which isn't in line with the aerial gain curve?
Actually I don't have any other TVs anywhere - I installed the amp when my daughter came back to live for a while, and I put in an aerial point in another room for her - but since she left we haven't had a second TV. So I can carry on without the amp, but do you think it might be worth trying to put in some variable gain and find a sweet spot where Ch 48 is improved without overload on the others?
I'll do some more playing around next weekend.
Thanks for your continued assistance. Is this a hobby? I am impressed by your tolerance and politeness when responding to people with a wide range of attitudes!
Alan
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Wednesday, 11 November 2020
C
Chris.SE10:56 PM
Alan_C:
It's not specifically anything "operating" on 690MHz, it's anything that might possible generate some interference to that frequency. In the expression "electronic control"/ powered all the time that would include anything with a SMPS (perhaps I could have been more explicit) so things like Mobile Phone chargers, USB power supplies etc. could all be suspects.
As it seems that the amp is not a likely source of issues for the C48 problems, unless repositioning of the aerial causes a significant uplift of the signal for the other multiplexes, not just SDN and COM7 (C48 & C55) then it's probable that you'd benefit from some amplification but not (necessarily) the full amount the amp can give.
You might find for example that you can get an uplift in C48 & C55 moving the aerial but you might get a slight drop in the others, so amplification to bring them all up would be a good idea.
By using a variable attenuator, you can hopefully tweak it to get the best compromise. You'd put it between the amp and the set, not aerial and amp. If you highlight the whole of that eBay url and open it in a new tab say, or search eBay for the item number - just the number, no words, it'll take you straight to it. There are other suppliers on eBay and on other sites, but not necessarily at such a good price for that - quite good - brand. If you go elsewhere, watch that you want coax connectors not F-connectors.
Hobby? Haaa, well, it was onetime work, these days it helps keep the brain active, but it's sometimes difficult to remain polite when you get some posts like two on the previous 2/3 pages here!
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Saturday, 14 November 2020
A
Alan_C7:56 PM
Somerton
Chris.SE:
An interesting and initially frustrating day spent tweaking things and hoping to improve reception of channel 48 from my loft aerial.
I tried checking for signal from Stockland Hill and Wenvoe (without turning the aerial) and unamplified, I found nothing on any of the relevant channels (26+ etc.).
I tried isolating any possible source of interference, switching various things off - I think I found all the switch mode power supplies in the house. A search online suggested that the solar PV inverter in the loft (which is a switching design) was a potential problem, and I considered where I might add ferrites - but turning it off made no difference to the signal on Channel 48.
So I looked at the effects of rotating the aerial. I checked signal quality and strength as reported by the TV for Channel 48, and also Channel 33 as a reference. As well as rotation, I also moved the aerial a small amount along its axis (up to about 15cm) and sideways (about 5cm) but these didn't seem to make any difference. What did make a difference was when I lowered it a small amount (7cm) to allow enough room for it to turn. This resulted in noticeably lower signals on my reference channel.
I plotted all the results on a graph and it showed that the signal strength on Channel 33 had a maximum at 22 degrees; Channel 48 seemed to indicate a peak around 30 degrees but it never rose enough to get a decent signal quality; the maximum was about 25.
So I concluded that the aerial was already pointing in the best direction possible for that location, but then I thought again about the height effects and put it as high as possible while horizontal; then angled it up by 15 degrees. The results are as follows:
Channel Horiz. Quality Horiz. Strength +15deg Quality +15deg Strength
32 95 60 100 70
34 100 70 100 75
35 45 60 60 60
48 50 65 95 70
33 95 70 100 70
36 55 65 85 65
As you can see, angling it upwards has improved the signal across the board, presumably because it is capturing signal which is coming through the tiles rather than the gable wall.
So I now have satisfactory reception on Channel 48, as well as the others. It hasn't explained why that channel was so much more affected by the wall than the others.
In closing, very many thanks for your help and support, and I'm glad to say the outcome is looking good.
Alan
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Alan_C's: mapA's Freeview map terrainA's terrain plot wavesA's frequency data A's Freeview Detailed Coverage
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