All posts by Steve Donaldson
Below are all of Steve Donaldson's postings, with the most recent are at the bottom of the page.
Adam Jackson: I should add that in the above two postings the numbers are bearings in degrees. I typed them with a degree-symbol but the website has removed this character!
The MoU figures are "from 102degrees to 128degrees (for Carmel), and -3dB from 129degrees to 135degrees (for Stockland Hill)." The St Davids transmitter is about 7 degrees clockwise of Trefin, is what it is meant to say.
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Adam Jackson: In addition to that said by Chris.SE (see comments from him and me on the previous page), it appears you almost have line-of-sight to Divis at 186 miles on a bearing of 350 degrees. The only obstruction is Garn Fawr. Line-of-sight leaves Northern Ireland between Newcastle and Dundrum.
The bearing of Mt. Leinster is 300 degrees, give or take a degree. So Divis is 50 degrees clockwise. Thus, another possible suspect cause is Divis, and if it is then perhaps turning the horizontally polarised Mt. Leinster aerial a little anti-clockwise might help null it. That said, the signal may be weak and so it's possible you can't afford to turn the aerial off-beam (unlike I imagine the one for the Trefin relay).
If your difficulty is interference from Divis then this is all the more reason to check aerial manufacturers' polar diagrams, as Chris.SE says. Also, consider whether there is anywhere the aerial could be mounted which allows sight in the direction of Mt. Leinster but where there is something in the way of Divis.
Divis' PSBs are 27, 21 and 24 @ 100kW, and COMs 23, 26 and 30 @ 50kW. If you are so inclined to swing the horizontal aerial round to try it out, then be aware that Blaenplwyf's PSBs are co-channel on 27, 24 and 21, on a bearing of 59 degrees, with only the moors around Rhos-y-Caerau blocking line-of-sight. Blaenplwyf's COMs aren't co-channel with those of Divis.
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Darren Brown: As I think you know, you aren't in a good reception area at all. The fact that aerials along the street are pointing to the three different transmitters is testament to this being the case.
Pontop Pike is the closest transmitter, and also the most powerful. While it is 16.6km / 10.3 miles away. In the direction from the transmitter to your location, the terrain rises up at Wrekenton, in the area of St. Oswald's Church and Lidl on Old Durham Road. This is a little less than 2 miles out. The ground rises to Black Hill and drops from Hill Top School. That line-of-sight (or what would have been LoS) is close to the ground between the school and your location means that buildings and trees on the ground are in the way, potentially hampering reception for you. So, in short, you have LoS obstruction from 2 miles out.
See this terrain plot for Pontop Pike:
Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location
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Darren Brown: As per Chris.SE's comment, I would wait until engineering works have finished then reassess the situation.
The distance from you to Bilsdale is only about 300 metres more than from you to Chatton. Bilsdale is more powerful though.
I can see potential causes of difficulty with reception from Bilsdale being the trees behind the houses on Sheraton (in the direction of Leam Lane), the fact that the ground rises upwards to George Washington Golf Club and possibly traffic passing on the A194(M). It is also the case that there is high ground east of Durham, which while not necessarily blocking line-of-sight, is within the Fresnel zone. This includes Haswell Moor, on which there are wind turbines.
See the terrain plot for Bilsdale:
Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location
So all in all, there is no one transmitter that stands out as likely to be better than the other two. They all have their challenges.
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Adam Jackson: With respect to reception from Preseli, this is made difficult due to several obstructions. Several of the Preseli Hills at 12 miles out are in the way. At about a mile out there is the quarry at Clegyrn. Immediately to the east of St. Nicholas is high ground and there is a gap where it drops down.
You can see these here:
United Kingdom topographic map, elevation, terrain
You can use this tool to draw a line between you and the transmitter:
Solwise - Surface Elevation Tool | Solwise Ltd
The height of Preseli transmitter is 235m, and you can enter this on the tool once a pin has been dropped.
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patrick: Heathfield doesn't broadcast the BBC FM nationals. The high-power transmitter which covers much of the south east is Wrotham. The Hastings TV transmitter also relays the BBC FM nationals.
Wrotham:
BBC Radio 2 = 89.1
BBC Radio 4 = 93.5
Hastings:
BBC Radio 2 = 89.6
BBC Radio 4 = 94.2
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paul : The above posting of 7th August from "Transmitter engineering" is that taken from the Freeview page "Planned engineering works":
Planned engineering works | Freeview
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David Nicholls: I suggest it "might" be engineering works at the Sandy Heath transmitter.
Judging by their location and transmission powers, Daventry and Sandy Heath are the transmitters much responsible for Digital One in your area. Thus, if one is off, you may have only the other.
This is speculative because there is no information as to engineering works on DAB. Freeview reports engineering works at Sandy Heath, with "Pixelation or flickering on some or all channels". This therefore points to works of some description going on at the transmitter site and possibly on the mast itself.
Unlike other broadcast systems, with DAB all the transmitters broadcast on the same frequency for the same multiplex (which carries an ensemble of radio stations). The transmitters send out the signal in time with one another meaning any one receiver could be getting some level of signal from more than one transmitter, varying by location. In such a situation, the signals from each transmitter add up to provide a better signal than had just one or fewer transmitters been available.
The radio stations you mention are carried on the Digital One national multiplex. Assuming you are in Northampton, having consulted a map of the transmitters around the area, Daventry and Sandy Heath are mainly responsible for Digital One in your area.
The Northampton DAB transmitter carries the BBC National multiplex only, hence it won't help you with Digital One in the event of any reduction or outage of the Sandy Heath transmitter.
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David Nicholls: Further to the above, here is some more information.
Taking the Kingsthorpe Golf Course as the sample location (don't ask me which hole) I have come up with the following transmitters. For each there is distance in kilometres, distance in miles, bearing in degrees, total effective radiated power and attenuation in direction of the sample location. They are ordered in what I think are the level of signal contributed to the sample location:
Daventry 17.4km 10.8mls 267deg 9.7kW -3dB
Sandy Heath 46.4km 28.8mls 108deg 4.7kW -2dB
Bow Brickhill 32.8km 20.4mls 153deg 2.6kW -2dB
Peterborough 45.9km 28.5mls 53deg 5kW 0.5dB
With respect to Waltham, it is 60.3km or 37.4mls away on a bearing of 5degrees (so 185deg out from the transmitter). The ERP is 8.8kW, and at 180deg it is 6.2dB down and at 190deg is 2.6dB down. At 170deg it is 11.9db down and at 200deg it is 6.5dB down.
Line-of-sight is badly blocked to Peterborough, so the conclusion to my findings reaffirms what I said previously, which is that Daventry and Sandy Heath are mainly responsible for the Digital One signal in Northampton.
If it's Sandy Heath that's off air then siting the radio somewhere where there is a clearer path to Daventry might help reception. If Daventry is off then siting the radio where there is a clearer path to Sandy Heath might help reception.
"Clearer path" is to mean, for example, at the side of the house facing the transmitter, and even better at an upstairs window. Daventry and Sandy Heath are in opposite directions. With all this information, if you go to a window that faces westwards to Daventry and get a better signal than one that faces eastwards to Sandy Heath then this may indicate the latter is off air or on reduced power, if indeed a DAB transmitter is ever put on "reduced power".
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Sunday 23 July 2023 7:09PM
Adam Jackson: The St. Davids relay transmitter uses C23 and C26, vertically-polarised. It is about 7 clockwise of Trefin from St. Nicholas. Prior to 700MHz clearance both St. Davids and Mt. Leinster were co-channel on C23 and C26, so nothing has changed there.
That the Trefin relay uses C22, C25 and C28 means it's not possible to filter the Trefin aerial. However, it may be worth considering that the difficulty isn't the fading of or interference to the Mt. Leinster signal from the Mt. Leinster aerial, but increasing signal from St. Davids on the Trefin aerial.
At such times, it would be worth removing the Trefin aerial and reverse-splitter from the equation. If this cures things, and the signal directly from the Mt. Leinster aerial is good, then perhaps turning the Trefin aerial a bit anti-clockwise off-beam might help nullify the unwanted St Davids signal.