All posts by Steve Donaldson
Below are all of Steve Donaldson's postings, with the most recent are at the bottom of the page.
nick : Aldeburgh is currently broadcasting 3 multiplexes at 10kW each. The former analogue consisted of four 10kW channels. Assuming the antenna hasn't been changed (the mb21 Transmitter Gallery doesn't say it has) then perhaps it may need changing in order to take the COM multiplexes, even if they were to operate at half the PSB power.
There is no need to worry that the Aldeburgh transmitter may buck the trend by changing from Group A to Group B in order to become SFN with Sudbury. "If" it were to broadcast the COMs they will be on channels 26, 30 and 32, as these are the channels that have been co-ordinated by international neighbours for that station.
| link to this comment |
Paul Fearn : This is a Coverage Plan document, dated September 2008, published by the BBC:
https://downloads.bbc.co.….pdf
As with the NGW report I referenced above, it was in preparation for DSO. It lists all transmitters as per the JPP (Joint Frequency Planning Project) Plan version 5.5.
It gives the location of the proposed Bridlington transmitter as Buckton Barn, with a power of 1kW per channel.
The question of where a new TV transmitter for Bridlington might be situated is a difficult one for planners, I think it's safe to say. I think ideally it should be to the south of the town because existing aerials are all pointing that way, and many people will be able to use it without needing to adjust their aerial. The problem in trying to achieve this is that the ground is flat to the south. There is high ground to the north, with a little to the west. There is already a lattice tower at Buckton Barn, used by mobile phone operators, Greatest Hits Radio on 102.4MHz and several DAB multiplexes.
What is more, paragraph 6.5 of the BBC Coverage Plan states, "In consultation with Ofcom and the other broadcasters, the BBC has agreed to build a small number of additional transmitting stations as part of the digital television network. These stations do not transmit analogue television as at the date of the Agreement. These stations are marked with an asterisk before their name in this section."
Bridlington, along with the other eight listed above are present in this BBC document with an asterisk.
So what happened? Why did Bridlington get canned?
I think it may be useful to see the JPP Plan. I wonder if it gives such detail as the reason for the transmitter, the number of people the transmitter would bring reliable service to whose reception (from Belmont) is otherwise marginal or below marginal. This situation cannot have changed to this day, and therefore justification for the transmitter given by the JPP back then still holds, hence why I say it might be useful to see it.
I also wonder if a subsequent version of the Coverage Plan sets out the reasoning for not building the Brid transmitter.
---
In a 2013 consultation response to Ofcom, Digital UK (a consortium of the BBC, ITV, Channel 4 and Arqiva) tears into Ofcom on the matter of the erosion of acceptable level of coverage. The subject of the consultation is the use of "white space" in the TV band of frequencies for uses other than broadcast TV.
Under the subheading "Degradation of DTT coverage thresholds" Digital UK says, "We are *concerned* that the starting point for this Consultation is that degradation of existing DTT reception, a licensed service, to permit the introduction of TV white space, a licence-exempt service, is both inevitable and acceptable." The asterisks indicate words emboldened in the consultation response.
The next paragraph opens with the sentence, "We are *concerned* that this proposed change comes on top of the fact that the definition of what constitutes a DTT service has been, and continues to be, eroded, with each change seeming insignificant compared to the previous position, but which cumulatively constitute a significant move."
It goes on to list several bullet points following the statement: "The changes in DTT coverage definitions over the years have been a matter of public record, as set out in the following statements and extracts from the relevant documentation:"
[two bullet points which I have omitted set out how the TV coverage threshold has been revised downwards]
The final two bullet points are as follows:
[Quote]
- The broadcasters were obliged to commission the construction of additional relay transmitters as part of the Digital Switchover programme to ensure the continuing availability of a terrestrial television service in parts of the country where conversion of the existing transmitter network would not provide an adequate service after switchover, i.e. the 70% location threshold was not met. The new transmitters include those at Bexhill, Clacton, Rouncefall, Skelmersdale and Budleigh Salterton.
- Some areas of the country (e.g. parts of Bridlington and the South and East coasts) fall outside of official 3PSB marginal coverage but Ofcom agreed that a relay would not be provided as part of switchover on the basis that no suitable site was available and households in these areas were already using significantly better than standard receiving installations. Protection of reception in such areas is therefore required but is not addressed in this Consultation.
[End quote]
The response also says that the JPP has since become the DTT Frequency Planning Board. I wonder whether some 10 years later it is still called this.
Source reference for this Digital UK consultation response: https://www.ofcom.org.uk/….pdf
| link to this comment |
Ed: Since digital switchover, The Wrekin, Bromsgrove and Lark Stoke have been operating as a single-frequency network (SFN). This is where they all share (and broadcast on) the same UHF channels (frequencies). They must be in sync (in time) with one another.
I wonder if your aerial picks up Bromsgrove to some degree and that the poor signal quality is as a result of the two signals being too out of time, i.e. one degrading the other turning the signal to mush. A more in-depth explanation of single-frequency networks follows.
From digital switchover (DSO), all six multiplexes of these three transmitters changed to being on the same channels (i.e. operating as a SFN). At 700MHz Clearance in 2018, Bromsgrove and Lark Stoke changed the three COM channels to 33, 36 and 48. The Wrekin did not change, and retains 41, 44 and 47 to this day. Consequently, the PSBs are the same and the COMs are different. The Wrekin is on 26*, 23*, 30*, 41, 44 and 47. Bromsgrove and Lark Stoke are on 26*, 23*, 30*, 33, 36 and 48. The asterisks denote that they are SFN. The other channels aren't SFN.
While not scientific, it may be interesting to see if any signal is available on 33, 36 and 48 as if there is then it/they must be coming from Bromsgrove 7 miles away. It might be indicative of 26, 23 and 30 being received from Bromsgrove at your aerial, those shared with The Wrekin. While Bromsgrove is vertically polarised (and your aerial is horizontally polarised for The Wrekin), it is in almost the opposite direction to The Wrekin, just 22 degrees of being so.
The Wrekin is 23 miles away. You would have line-of-sight were it not for Ridgehill and the trees on it at 1.5 miles out.
To return to the point about The Wrekin and Bromsgrove PSB muxes (26, 23 and 30) being SFN, you are in the area of overlap where both signals may be available. Those, say, in Wolverhampton and Telford are far enough away from Bromsgrove (and Lark Stoke) that they will receive only The Wrekin.
None of this is to say that your issue is down to the SFN. The SFN is one possibility to consider, another being the phone mast.
_____
- Signal Frequency Networks -
As an example, DAB radio uses SFNs. A SFN is different to the more familiar multi-frequency network such as FM radio, where each transmitter broadcasts on its own channel, one which is different to neighbouring transmitters because they would interfere with one another otherwise. I should say that in most cases that the current digital TV transmitters do operate as a multi-frequency network, not as SFN. Here we have one of a few cases of them working as a SFN.
Of course, with a SFN what is received and when varies by location. By this, I mean where more than one transmitter in the SFN can be received then usually one is received first and then the other (as with a sound echo). The one that is received the first is the closest, signals travelling at the speed of light. Were one to be exactly half way between the two, the signal from each would arrive at exactly the same time and therefore the receiver would get a larger-magnitude signal than with just one of the transmitters alone.
It follows then that the degree of echo between the two (or more) transmitters will vary by location. Digital receivers are fine with receiving two or more signals that don't arrive at exactly the same instant -- they are fine up to a point, hence why the transmitters must be in time with one another. If they are not then there will be locations where the two overlapping signals are too much out of sync, meaning the delay/echo is too long, which means the receiver can't decipher it and the signal is "mush".
Think stood in a railway station with a huge arching roof and trying to listen to the announcement over the PA system. You are close to one of the speakers and can hear the speaker were it not for the fact that the echo of previous words are bouncing off the roof and walls being so loud and drowning it out.
| link to this comment |
Ed: Having read your posting again, I see it's most channels that are the problem, not just the one BBC channel which I had incorrectly understood it to be when I wrote about the SFN. That it affects the COM channels means it cannot be anything to do with the SFN.
| link to this comment |
Roger Haworth: If you haven't already done so, the first thing to check is that the TV is in fact tuned to the desired transmitter and not another, distant one, as this is a common reason for poor reception.
ITV, C4, C5 and some others are carried on PSB2 multiplex, which is on UHF channel 36 (594MHz) from Widecombe In The Moor transmitter. If the signal strength screen gives the channel/frequency you are tuned to, it should say this.
The Widecombe In The Moor transmitter sits to the south east of the village, beaming north westerly, thus aerials are facing roughly in the direction of Beacon Hill. PSB2 from Beacon Hill is on C41(634MHz). PSB2 from Caradon Hill is on C25 (506MHz) and is thus picked up first during the scan, when performing automatic tuning. It is possible, then, that the TV could have opted for this, even if it hasn't done so in the past, being that it is a distant signal and may vary at different times.
| link to this comment |
Liam Williams: Looking at the map of transmitters, I think Blaenplwyf is really the only DAB transmitter you might possibly receive, at just over 8 miles out. The problem is that you are in a valley and it doesn't run in the direction of the transmitter, hence the terrain is casting a shadow.
Blaenplwyf transmits two of the national multiplexes, the BBC National being far more likely to be able to be received than the D1 National, this because the antenna transmitting the BBC multiplex is higher up the mast and the strength of the signal coming in your direction is much stronger.
Here are the details of the Blaenplwyf DAB transmissions. For each multiplex I have given the channel number, the height of the transmitting antenna above ground, the effective radiated power of transmitter, the number of dBs down in your direction and, in brackets, the effective radiated power in your direction:
BBC National: 12B 125m 4.67kW -2.0dB (2.94kW)
D1 National: 11D 83m 1.4kW -2.7dB (0.752kW)
From these figures, what is really of interest are the facts that the BBC antenna is higher up. As the terrain is anything but flat, it casts shadows. The shadows will be larger the lower down the antenna is. The other thing to note is the that the D1 National antenna is throwing out a much less powerful signal in your direction than the BBC one. If you're struggling to get the BBC then you aren't likely to get the D1 multiplex.
The transmitter isn't omnidirectional, meaning the full signal power isn't being thrown out around all 360 degrees. The dB figure is the amount it is down on the full signal power on a bearing of 20degrees out from the transmitter (in the direction Dol-y-Bont), hence I used this to calculate the power in the direction of Dol-y-Bont (shown in brackets).
There is a BBC National transmitter at Machynlleth, but this is blocked by very high ground and too weak in your direction to be of any use.
The next two DAB transmitters distance-wise and that are of any significant power are Arfon (39 miles) and Presely (45 miles). I mention them not because I think you might be able to receive them, because these are the "next best", hence why I say I think that your only possibility, if any, is Blaenplwyf.
Thus, your most likely chance of reception is in the direction of the Blaenplwyf transmitter. And if you're struggling to get the BBC National on 12B, you aren't likely to get the D1 National on 11D.
| link to this comment |
Martin Hamilton: You might consider Freesat in order to receive more channels. Here are the list of channels provided by Freesat:
Channels List and On-Demand Players | Freesat
For comparison, here is the full list of channels available via Freeview:
Channel listings for Industry Professionals | Freeview
The "mux" column identifies which multiplex they are on. The main six multiplexes are:
PSB1 = BBC A
PSB2 = D3&4
PSB3 = BBC B
COM4 = SDN
COM5 = Arq A
COM6 = Arq B
The Rosehearty transmitter carries PSB multiplexes only. The list contains other multiplexes than these six which are available in some particular areas.
| link to this comment |
Ed: While one plausible explanation for the symptoms described is an issue with the aerial or cabling, the phone mast could still be the cause. This is because it appears you have an amplifier, possibly sited with the aerial, this implied by the Fringe power unit, which is intended for powering an amplifier.
Ideally, filtering out of the phone signal needs to be before the amplifier because it could potentially overwhelm it. While it is the case that inserting the filter at the input of TV will filter out the mobile phone signal (which the amplifier has made bigger), the effect of the mobile signal on the amplifier could be to desensitise it to the (lower level) TV signal and distort it.
Prior to sending an engineer, the best Restore TV could do is send you some filters to put behind your TVs. If this resolved the issue, then that might be all good. If not, then a filter may need to go before the amplifier -- if the amplifier is necessary for your set-up. It sounds like this might require a waterproof filter suitable for outdoor use fitted on the roof, immediately after the aerial and before the amplifier.
The aerial input to the TV or set-top box is designed to accept signals within the range of frequencies used for TV. The top portion of those frequencies has now been given over to the mobile phone networks. Such networks can give rise to situations where the signal level of the (unwanted) phone signal(s) is/are substantially higher than those of the (wanted) TV signal. It is this marked difference in levels that is the problem.
Prior to the mobile phone networks being allowed to use the frequencies formerly used for TV, the only broadcasts in that range were from TV transmitters. Being that all signals sent out by any given TV transmitter are around the same level, they are received at the around same level at all locations. Today, there can be unwanted signals of much higher magnitude than the wanted TV signals in the range of frequencies TVs are designed to accept. This will vary by location -- it won't be the case everywhere.
The first stage of any receiver is to receive a signal on a particular designated frequency. It is only further on that the signal is interpreted, e.g. a TV receiver interprets and resolves a TV signal to the picture, sound and so on. It's at this first stage that the problem occurs. The problem is signal level, not type of interfering signal per se.
Think of walking along the pavement at the side of a busy road at night where there is very little to no light from streetlights. Car headlights desensitise your eyes to the darker pavement in front of you, thereby making it more difficult to see the way than had they not been there. The really strong mobile phone signal (from a nearby mast) is akin to the car headlights, your eyes are like the TV receiver and the pavement ahead is like the TV signal.
Adding the filter is like putting shades on that are able to reduce the brightness of the headlights while not reducing the level of the light ahead on the pavement (if such shades could actually exist). If the level of light from the headlights was around the same level as the ambient light on the pavement you would be able to see the latter. The presence of the former would not degrade visibility of the latter. Prior to mobile phone networks using what were formerly TV frequencies, there were no "lights" (signals) much brighter (stronger) than others in that range of frequencies.
| link to this comment |
barry hardwick: It may be worth looking on channel numbers 800 upwards. This is where duplicate channels are put. They may appear to be in no particular and there could be none, some or a lot, depending on what can be received.
In particular, the Oxford transmitter is the opposite direction to Sandy Heath and you might be lucky and be able to pick it up off the back of your aerial. ITV from Oxford is on UHF channel 44 and it may be worth doing a manual scan of that channel to see if it can be picked up. If your TV has already tuned it in then it will be in the 800s, as described above.
| link to this comment |
Monday 2 October 2023 6:34PM
Paul Fearn : As Chris.SE says, there is currently engineering works at Belmont. As you are on the very fringes, any reduction in output by the transmitter may be insufficient to serve you, and the most likely explanation may be that the transmitter is on low power or using the reserve antenna, which is lower down than the main one at the top.
Over the last 10 years or so, a number of new transmitters have been built to improve reception in poor areas. At digital switchover (DSO) and later at the 700MHz Clearance new transmitters came on air. The 700MHz Clearance programme occurred region by region between 2017 and 2020, reorganising TV frequencies in order to free the highest-most for use by mobile phone networks.
Prior to digital switchover in 2007, Bridlington was identified by TV-frequency planners as one of a nine places requiring its own transmitter. As detailed below, eight of these places saw the matter addressed at switchover -- only Brid was and still is outstanding. I suggest you write to your MP about this. Cite the report referred to below, pointing out that all but your location have had solutions put in place.
Also raise it with parish councils and the like, pointing out that this particularly impacts the elderly who often do not have or are not able to access TV broadcasts over the Internet. They may be isolated, relying on their TV for company and connection to the outside world.
Today, all TV transmitters are under the control of one company, Arqiva. In 2007, prior to DSO, there were two companies: Arqiva and National Grid Wireless (NGW). In preparation for switchover, these companies produced a "reference offer" report in which they provided details of their network of transmitters. Within the NGW document, Bridlington got a mention:
https://www.arqiva.com/do….pdf
See paragraph 4.6 on page 161 of the report (page 159 of the PDF). It says that the Joint Planning Project (JPP) had identified in its Spectrum Plan, nine locations, including Bridlington, in need of a new transmitter to alleviate poor reception. The JPP is chaired by Ofcom and includes Arqiva, the BBC and other broadcasters. The nine proposed transmitters were:
1. Rouncefall (South East Essex) -- Built. New at DSO. This by the River Crouch, upstream from Burnham-on-Crouch, and at 4kW is a second-most powerful relay in the country (joint second with Arfon in North Wales).
2. Broadstairs (Kent) -- No new transmitter. However, within a mile or so of Broadstairs are the transmitters of Margate and Ramsgate. At DSO, both had a considerable power increase.
3. Bridlington -- Not built.
4. Clacton (Essex) -- Built. New at DSO.
5. Lowestoft (Suffolk) -- Built. New at DSO.
6. Burnham-on-Crouch (Essex) -- Built. New at DSO.
7. Great Yarmouth (Norfolk) -- Built. New at DSO.
8. Budleigh Salterton (Devon coast) -- Built. New at DSO.
9. Bexhill (Sussex) -- Built. New at DSO.
As you can see, seven of these locations got a new transmitter, one other got increased coverage from two nearby transmitters and the other is Bridlington. Subsequently, at 700MHz Clearance, Sittingbourne, Gillingham, Ashford and Swindon saw coverage improved by way of new transmitters. In other places, there have been power increases at existing transmitting stations. This all goes to show it can be done.