All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Susab Bourchier: Without knowing where you are it's not possible to answer the question!
Midhurst broadcasts Film 4 and other Commercial channels, but their coverage is more limited than the Public Service channels of BBC, ITV1, Channel 4 and Channel 5. Thus, there are some who can only receive the Public Service channels and not the Commercial ones. In "some" cases an alternative aerial will allow reception of the Commercial channels.
If you provide your location, preferably in the form of post code or nearby post code (e.g. a shop), then a check can be made as to the likelihood of reception of the channels.
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Laura: It only six miles from the transmitter, the signal may be very strong. Consequently too much signal could be being fed to your receiver which is overwhelming it at times.
See Freeview news | ukfree.tv - independent free digital TV advice
Try fitting an attenuator inline with the aerial lead so as to reduce the level of signal. A 20dB variable one will allow adjustment. These can be obtained from online sources for £3 or £4.
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Peter: The answer depends on which transmitter you are using.
If you and your friend have your aerials directed to the Bury St Edmunds transmitter, then it doesn't carry these channels. It only carries the Public Service channels which are BBC, ITV1, ITV1+1, ITV2, Channel 4, Channel 4+1, E4, More 4, Channel 5 and the four HD services.
If you provide your location, preferably in the form of post code or nearby post code (e.g. a shop), then likelihood of reception can be checked upon.
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Colin: You should definately have your aerial vertical as the Commercial channels aren't as strong horizontally. The marked difference in strength can be an issue.
You may have too much signal, what with the transmitter being only five miles away:
Freeview news | ukfree.tv - independent free digital TV advice
The Rowridge mast can be seen in the photographs taken by Google Streetview on Chale Lane:
PO38 2LE - Google Maps
And Atherfield Road:
PO38 2LE - Google Maps
What's the reason for a high-gain aerial? Perhaps you should turn it the other way and point it at France!
If your aerial is a wideband one, which a look on the Philex site suggests that all SLx 48 models are, then it will have less gain at Group A channels, of which all of Rowridge's are.
There's no such thing as a high-gain wideband yagi aerial that has "high-gain" on Group A channels. See these curves:
Gain (curves), Again
Thus a high-gain wideband yagi aerial used on Group A channels isn't so high-gain.
As all Rowridge's channels are in Group A, where a high-gain aerial is needed, then it is best to go with a high-gain Group A aerial.
That said, why is a high-gain aerial required at only five miles with apparently good line of sight?
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Alain: To a lesser degree you vertical aerial will pick up horizontally polarised signals.
I have to say that when I made my posting, I was probably clutching at straws with regards a possible explanation.
A terrain plot shows that you are 50 miles from Midhurst with a few hills in the way, so it is probably unlikely to be the cause:
Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location
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Justin: I expect that it's just the lower power of the ITV signal. Wait until tomorrow and they will all be on full power!
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Farrah Day: I looked back at your previous postings to find that you are in Nuneaton and that The Wrekin is within a few degrees of Sutton Coldfield.
Have you confirmed that BBC One is tuned to Sutton Coldfield on C43 and not The Wrekin on C26? Likewise ITV1 should be C46 and not C23. HD services are C40 and not C30.
If you find that any of these are tuned to The Wrekin, run the automatic tuning scan with the aerial unplugged for the first 30% of the scan.
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Colin: If the problem is excessive signal, you may well have enough to distribute it to multiple rooms using an unpowered splitter:
Television Aerial Boosters / Amplifiers, Splitters, Diplexers & Triplexers
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Stuart Mcfarlane: Where is your aerial pointing and which multiplexes are missing?
If it is Sudbury, then the Commercial multiplexes are on low power until 27th June when a retune will be required in order to restore them.
If they have manual tuning, try it. Or try taking them to a different aerial outlet and see if they work then, if it is convenient.
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Tuesday 12 June 2012 1:03PM
Mike Dimmick: Thanks for the insight. I have some questions for you which I will be grateful if you can answer.
The PSB networks are different to the COM ones, coverage wise, with the latter being more restricted due to channels being re-used more often (distance wise from transmitters). I have seen that you have said that coverage is generally more often restricted by interference than propagation. Helping out on this site, I have seen a number of occasions where this has been seen to be so.
Some transmitters have COMs at the same ERP as the PSBs, but according to predictions, their will be some viewers who will only be able to pick up the PSBs. (See Freeview news | ukfree.tv - independent free digital TV advice )
Referring to the Arqiva "Reference Offer for the Provision of Network Access" (page 29), Emley Moor uses two sets of panels, one for PSBs and one for COMs. Both have an ERP of 174kW. Is it likely that the COMs antenna's beam is tilted lower than the PSB one (which might account for the difference in number of people served for each)? At my location, the COMs appear lower strength and turning the aerial off-beam, when the COMs start to break-up, the PSBs are still strong.
http://www.arqiva.com/cor….pdf
Then there are those whose COMs are at half-power to the PSBs. Midhurst is one such example and its Steyning relay currently broadcasts co-channel with two of Midhurst's COMs. This is an example which illustrates why the COMs are more restricted.
Midhurst isn't shown in that document, so take Stockland Hill as an example. It apparently uses one antenna system for all six muxes (all of which are in the 20s) and the COMs are at half the power of the PSBs.
Why do some transmitters have two antenna systems and some have one? I appreciate that where channels are far apart they are likely to have to have more than one. I presume that the tilt of the beam will be the same for Stockland's PSBs and COMs as it's the same antenna.
Is the answer to the question cost and the fact that there's little to be gained having different antenna systems with smaller transmitters and that reducing ERP is a much more effective (from a cost point of view) in restricting coverage?
Then there is Belmont. The PSBs are in the 20s at 150kW, COM4 is on C30 at 50kW and COM5 and COM6 are on C53 and C60 at 100kW each.
Obviously C53 and C60 can't have as big a footprint as the PSBs as these are re-used from Oliver's Mount, for example. Some in Filey receive from Oliver's Mount and some, including those low-lying on the sea front, receive from Belmont. So there is clear overlap.
The reason I mention Belmont is because of the apparent anomaly of COM4 being half-power to COM5 and COM6. Why is this?
According to the Arqiva document, the three PSBs and COM4 use one antenna system and COM5 and COM6 use another. This makes sense due to the channel spacings.
Is the reason that C30 is at lower power so that the signal doesn't carry as far (as it's being radiated from the PSB antenna)? And again, for cost reasons: instead of having three antenna systems; one for PSBs, one for COM4 (lower power and lower tilt that the PSBs) and another for COMs 5 and 6?
I am wondering if it is cheaper to restrict coverage by reducing ERP (for COM channels) whilst using the same antenna as the PSBs (e.g Midhurst, Stockland and Belmont COM4). But for the larger transmitters it is more financially viable to have two antenna systems, even where all channels are close to each other (e.g. Emley Moor and I presume Crystal Palace).