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Freeview Light on the Backwell (North Somerset, England) transmitter

first published this on - UK Free TV
sa_gmapsGoogle mapsa_bingBing mapsa_gearthGoogle Earthsa_gps51.441,-2.724 or 51°26'28"N 2°43'25"Wsa_postcodeBS48 1NY

 

The symbol shows the location of the Backwell (North Somerset, England) transmitter which serves 4,600 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.

This transmitter has no current reported problems

The BBC and Digital UK report there are no faults or engineering work on the Backwell (North Somerset, England) transmitter.

Choose from three options: ■ List by multiplex ■ List by channel number ■ List by channel name
_______

Which Freeview channels does the Backwell 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.

MuxH/VFrequencyHeightModeWatts
PSB1
BBCA
 V max
C25 (506.0MHz)125mDTG-19W
Channel icons
1 BBC One (SD) West, 2 BBC Two England, 9 BBC Four, 23 BBC Three, 201 CBBC, 202 CBeebies, 231 BBC News, 232 BBC Parliament, plus 17 others

PSB2
D3+4
 V max
C28 (530.0MHz)125mDTG-19W
Channel icons
3 ITV 1 (SD) (West), 4 Channel 4 (SD) South ads, 5 Channel 5, 6 ITV 2, 10 ITV3, 13 E4, 14 Film4, 15 Channel 4 +1 South ads, 18 More4, 26 ITV4, 28 ITVBe, 30 E4 +1, 35 ITV1 +1 (West),

PSB3
BBCB
 V max
C22 (482.0MHz)125mDTG-19W
Channel icons
46 5SELECT, 101 BBC One HD West, 102 BBC Two HD England, 103 ITV 1 HD (ITV Meridian Southampton), 104 Channel 4 HD South ads, 105 Channel 5 HD, 106 BBC Four HD, 107 BBC Three HD, 204 CBBC HD, 205 CBeebies HD, plus 1 others

H/V: aerial position (horizontal or vertical)

Are you trying to watch these 44 Freeview channels?

the effected channels
the effected channels
the effected channels
the effected channels

The Backwell (North Somerset, England) mast is a public service broadcasting (PSB) transmitter, it does not provide these commercial (COM) channels: 4seven, 5Action, 5STAR, 5USA, Al Jazeera Eng, Al Jazeera English, Blaze, Blaze +1, Challenge, Channel 5 +1, Dave, Dave ja vu, DMAX, Drama +1, E4 Extra, YAAAS!, Film4 +1, Food Network, GREAT! action, GREAT! movies, GREAT! romance mix, GREAT! romance, HGTV, HobbyMaker, ITV2 +1, ITV3 +1, ITV4 +1, ITVBe +1, Legend, PBS America, Quest +1, Quest Red, Really, Sky Mix, Sky News, Talking Pictures TV, TCC, That's 90s, That's TV 2, Together TV, TRUE CRIME, TRUE CRIME XTRA, W, Yesterday +1.

If you want to watch these channels, your aerial must point to one of the 80 Full service Freeview transmitters. For more information see the will there ever be more services on the Freeview Light transmitters? page.

Which BBC and ITV regional news can I watch from the Backwell transmitter?

regional news image
BBC Points West 0.9m homes 3.4%
from Bristol BS8 2LR, 8km east-northeast (75°)
to BBC West region - 60 masts.
regional news image
ITV West Country News (East) 0.9m homes 3.4%
from Bristol BS4 3HG, 11km east (90°)
to ITV West region - 61 masts.
All of lunch, weekend and 50% evening news is shared with West Country (West)

How will the Backwell (North Somerset, England) transmission frequencies change over time?

1984-971997-981998-20102010-135 Jun 2019
A K TA K TA K TA K TA K T
C22BBC1wavesBBC1wavesBBC1wavesBBCBBBCB
C25ITVwavesITVwavesITVwavesBBCABBCA
C28BBC2wavesBBC2wavesBBC2wavesD3+4D3+4
C32C4wavesC4wavesC4waves

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 94W
BBCA, D3+4, BBCB(-6.9dB) 19W

Which companies have run the Channel 3 services in the Mendip transmitter area

Jan 1958-Jul 1968Television Wales and the West
Jul 1968-Feb 2004Harlech Television
Feb 2004-Dec 2014ITV plc
Feb 1983-Dec 1992TV-am•
Jan 1993-Sep 2010GMTV•
Sep 2010-Dec 2014ITV Daybreak•
• Breakfast ◊ Weekends ♦ Friday night and weekends † Weekdays only. Backwell was not an original Channel 3 VHF 405-line mast: the historical information shown is the details of the company responsible for the transmitter when it began transmitting Channel 3.

Comments
Thursday, 11 April 2024
P
Paul Dursley
8:04 PM

Chris.SE:
Evening.
The connector box on the aerial looks complete and intact through my binoculars - nothing obviously untoward.
A new coaxial cable has made no observable difference, i.e. no change to pre-existing signal strengths and quality. I'll keep the DVD HDMI cable away from the coaxial as best I can.
I do notice that C22 does seem to vary in signal quality dependant atmospheric conditions, so dull and dank gives poorer signal quality 4 to 5/10; bright and dry seems to take the quality level up to 6 to 7/10.
Looking forward to receiving an inline filter to see if this makes any difference.

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Paul Dursley's 13 posts GB flag
S
Steve Donaldson
sentiment_satisfiedSilver

10:09 PM

Paul Dursley: Bristol Kings Weston is co-channel with Backford and it is on nearly the same bearing for you.

During the 700MHz Clearance, UHF channels 49 to 60 were cleared of TV broadcasts, with all transmitters on those channels having to move down. Consequently, with fewer broadcast channels to go around, some transmitters ended up on the same channel when previously they were not.

In your area, the change happened on 5th June 2019 (except for one of Kings Weston's channels which changed two weeks later).

Backwell used channels 22, 25 and 28 before the change. The COMs of Kings Weston and the PSBs of Ubley changed.

Bristol Kings Weston COMs: 53, 57*, 60- changed to 22, 25*, 28
Backwell: No channel changes. Power up from 18W to 37W.
Ubley: Power up from 15W to 25W. 21+, 24, 27 changed to 22, 25, 28

* Kings Weston C57 changed to C25 on 19/06/19.

Kings Weston is on a bearing of 37 degrees at 7 miles out. Backwell is on a bearing of 31 degrees at 2 miles out.

Like Backwell, Kings Weston is vertically polarised. Kings Weston is 200W, much of which is coming in your direction, the radiation pattern being generally to the south from the tower (see the page on this site for Kings Weston).

I think the power increases at Backwell and Ubley were an effort to counter co-channel interference rather than to increase coverage. Similar power increases occurred elsewhere in similar circumstances.

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Steve Donaldson's 199 posts GB flag
S
Steve Donaldson
sentiment_satisfiedSilver

10:35 PM

Paul Dursley: My apologies, I meant to say 'Backwell', not 'Backford'.

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Steve Donaldson's 199 posts GB flag
Friday, 12 April 2024
C
Chris.SE
sentiment_very_satisfiedPlatinum

12:48 AM

Steve Donaldson:

Whilst your theory about the increases in power is probably correct, the geography (the seven hills that surround Bristol) suggests that the signals from Kings Weston will not reach the coverage areas of Backwell or Ubley, close but not quite, in normal circumstances.
Whilst I haven't bothered to do a line of sight analysis, I would have expected the computer modelling used by the frequency planners to have addressed this ok.

Paul Dursley:

Another check that you might try, is look at as much of your coax downlead as you can, especially any parts that are exposed to direct 'heat of the day' sunshine. Look for cracks, brittleness or bits of sheath that may be missing.

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Chris.SE's 4,128 posts GB flag
S
Steve Donaldson
sentiment_satisfiedSilver

2:32 PM

Chris.SE: It would appear that, while it is fairly close distance-wise, Kings Weston is screened from the Backwell coverage area.

There is a ridge which is at least as high as the level of Kings Weston's antennas. Backwell transmitter sits on the way down from this ridge.

The height above ordnance datum of the Kings Weston antennas is 138m. Between Kings Weston and Paul, the highest point is around 160m, this 4.2 miles out from the Kings Weston transmitter and about 3 miles out from Paul. Paul's ground level is 18m.

The Kings Weston transmitter is currently 250W on the six, main channels, this according to the Freeview Coverage Checker, and Version 20 of the Ofcom Table of Digital Terrestrial Broadcasting Stations for Multiplex Licences, dated 5 February 2020. The previous version of the multiplex licence document is dated 6 June 2019, and sets out the aforementioned channel changes, but gives the power of the six multiplexes as 200W, which they had been since DSO. So it would seem that a decision was taken to increase the power sometime in the second half of 2019 or the first few weeks of 2020.

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Steve Donaldson's 199 posts GB flag
Saturday, 13 April 2024
P
Paul Dursley
6:17 PM

Steve Donaldson:
Evening
Inline filter received and fitted - made absolutely no difference to C22 signal strength or quality; C25 and C28 unaffected.
Still, the original issue is 'resolved' in so much that I am receiving the BCC West HD and other C22 TV channels.
Not sure where that leaves the us with the discrepancy of signal strength and quality for C22 vs. C25 and C28 from the Backwell transmitter.

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Paul Dursley's 13 posts GB flag
S
Steve Donaldson
sentiment_satisfiedSilver

7:31 PM

Paul Dursley: Considering what I have found, which follows below, I'm not surprised the filter has had no effect. I believe this is an issue with reception of Mendip by the Backwell transmitter and needs reporting to the BBC.

The signal path between the Backwell transmitter and Mendip runs close to the ground for around a mile where it goes over the top of Barrow Hill. The signal path is the line through free space between the transmitting aerial of Mendip and the receiving aerial of Backwell. I think this is why there are two receive aerials on the Backwell transmitter.

I suspect the reason you lost reception of PSB3 (C22) and at the same time had lower quality on PSB2 (C28) is because Mendip was broadcasting from its reserve antenna. This is lower down the mast than the main which is at the top. I think that PSB3 came back because Mendip returned to transmitting from its main antenna.

The three Mendip channels for the PSBs are C32 (PSB1), C34 (PSB2) and C35 (PSB3). If your issue is in fact a reception issue for the Backwell transmitter then when you lost PSB3 it was C35 that was worst impacted with C34 less so (you had lower quality on PSB2). If this was because Mendip was on its reserve antenna and now it is on its main, then the quality issue on C22 may in fact be a quality issue on C35 as received by the Backwell transmitter.

Thus, it looks like the objects in the signal path between Mendip and Backwell are acting to the detriment of reception in the frequency range of C35 (around 586MHz). With the lower height of the reserve antenna the obstruction in the path increased, and when this happened the impact on reception on C35 frequencies became more pronounced, spilling over into the adjacent channel, C34.

- Terrain Plots -

I have set out the aerial heights below. Here is a terrain plot with Backwell on the left and Mendip on the right:


Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location


The plotter uses six-figure OS grid references, meaning the locations of the two transmitters are set to the 100m interval closest to where they are. Backwell is set a few tens of metres away from its true location where the ground height is a little higher, so I have compensated by reducing the height of the antenna. For the height of the Mendip antenna I have entered that of the lower/bottom of the reserve, so we can see worst-case scenario, with Mendip transmitting from its lowest antenna.

The yellow line denotes the line-of-sight and the pink line is the outer of the first Fresnel zone. The Fresnel zone is the area between the pink line and yellow line. Anything in this area can have the potential to affect reception. This isn't to say that it will, but we can see that the ground and objects on it are in the Fresnel zone for around a mile, from somewhere about 2.6 miles out to maybe 3.7 miles out from Backwell. This corresponds roughly to a line over Barrow Hill from about The Conygar (around Water Catch Farm) through to the high ground of Yewtree Farm, which is to the south of Freemans Quarry and north of the A38.

The point then is that the lowering in height of the Mendip antenna (by way of switching from main to reserve) increases the level of obstruction in general present in the Fresnel zone (the Fresnel zone having lowered also). Increasing its height by returning to the main reduces the obstruction.

This is a plot from the Backwell receive to the bottom of the Mendip main antenna:


Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location


- Aerial Heights -

Ofcom publishes the average aerial heights of transmitting antennas (main, not reserve). I referred to planning application diagrams for the height of the Backwell receive, and Mendip main and reserve antennas height spans (source reference notes in square brackets):

-- Backwell --

Site height: 96m
Receive aerial height above ground: 23m [1]

-- Mendip --

Site height: 303m
Main antenna height: from 282.3m to 293.7m [2]
Reserve antenna height: from 245.7m to 257.2m [2]

~~

The Mendip source [2] was published in 2013 and therefore with the previous Mendip antennas, as they were subsequently replaced for 700MHz Clearance. However, the current ones are in the same place, so the figures will be still relevant.

As can be seen in photos[3], between the main TV and reserve TV aerials are DAB and FM broadcast antennas. I checked the height of these other antennas and they are between the main TV and reserve TV heights quoted above, so those figures look to be right. The average height of the main TV is given as 288m, which ties in with the above.

We can see from this that the Mendip reserve antenna is 36.6m lower, from the bottom of the main to the bottom of the reserve.

_____

[1] Planning application 15/P/1969/F with North Somerset council, 'Proposed Elevation' document.

[2] Planning application 2013/1080 with Somerset Council, East District (former Mendip District), 'Existing SE Elevation' document.

[3] mb21 - The Transmission Gallery

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Steve Donaldson's 199 posts GB flag
C
Chris.SE
sentiment_very_satisfiedPlatinum

11:15 PM

Steve Donaldson:

Whilst I'm not going to dispute your terrain analysis and hypothesis which is always very thorough and very likely to be the cause of the problems, there is one statement that I will disagree with -
Quote "Considering what I have found, which follows below, I'm not surprised the filter has had no effect"

It is ONLY because the filter has had NO effect that it PROVES the problem is not related to Mobile Cell Interference and therefore supports the hypothesis you've presented.

Paul Dursley:

In a previous post you mentioned C22 signal Quality varying in certain weather conditions but implied that at best is was only 7/10. Would that be correct? And what sort of figure do you get for C28 in such conditions, I've got the impression that it's 10/10 for the most part.
This could also be relevant information when making a report to the BBC.

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Chris.SE's 4,128 posts GB flag
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