All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Peter berry: Which transmitter is your aerial directed to?
If it is the Saltdean relay then you will not receive ITV3 or any other Commercial channels from it because it doesn't broadcast them.
If it is Whitehawk Hill, then perhaps you are marginal. Do you get the other Commercial channels?
See this page and identify which of the COM multiplexes (if any) you get:
http://www.dmol.co.uk/mux….php
ITV3 is carried on COM4. So do you get COM5 (Pick TV) and COM6 (Yesterday)?
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Alex: Alex: It is unfortunate that, come switchover at Bilsdale, its COM multiplexes are interleaved with the PSBs of Emley Moor, else you may have been able to combine two aerials. I assume that you prefer to watch Yorkshire regional programming over that of North East/Tyne Tees if possible.
Emley's PSBs being 47, 44, 41 and Bilsdale's post-DSO will be 43, 46 and 40.
See this plot of the terrain between you and Emley Moor:
Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location
Looking at that plot, the reason that your area is marginal for Emley's signals is due to the high ground around Beckwithshaw and Rigton High Moor.
The problem you've got is that you don't have direct line of sight. Therefore, you are trying to "collect" what signal comes over the brow.
I'm not an aerial installer myself, but I have read that in situations such as yours that it might be better to use a lower gain aerial with amplifier. This makes sense.
The higher the gain of the aerial, the narrower the acceptance angle. This is because "gain" of an aerial (in one direction) comes about as a result of "loss" in other directions.
Digital reception requires a good quality signal. If you have a poor quality small signal and you amplify it, then you get a large poor quality signal. Whilst you can make a signal bigger with an amplifier, you can't make a poor quality signal a good quality one.
Where you have line of sight, clearly you can focus on the "beam". If you think of the signal as being a light, then where there is no direct line of sight, then you may get a "ball" of light shining over the brow. Any objects on the brow will therefore impact what you see. For example, if there are trees, then they will cause a shadow and probably moving shadow at that.
By using a high gain aerial, you are relying on a narrower portion of the "ball" of signal coming over the hill. A wider angle "may" give you a better quality signal.
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Alex: It is worth checking with Virgin Media which regional output is carried on the cable in your area.
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Nick A: The signal strength jumping up and down as you describe sounds like it could be signal overload, particularly bearing in mind your close proximity to the transmitter.
See this page for an explanation and remedy:
Freeview signals: too much of a good thing is bad for you | ukfree.tv - 10 years of independent, free digital TV advice
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Nick A: There are two factors with digital signals:
- strength: this is the level of the signal (level of voltage if you like)
- quality: digital pictures are resolved to digits (numberical values)
A poor quality signal means that the digits are not being received correctly and hence the picture breaks up or cannot be resolved at all.
Receivers have upper thresholds of signal strength that they can operate at.
A hifi system has a similar maximum level above which the signal starts to distort and therefore the quality reduces.
I imagine that when the strength of a digital signal gets to a level that is excessive (or bordering on excessive), then the effect is analogous to distortion of a hifi system's sound output.
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Jonathan: See
Satellite, Television, FM, DAB, Aerial, Coaxial Cable, Plugs, Sockets, Connectors & Leads
If you already have a cable from the aerial to the TV, then it is probably worth trying it as it is.
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Nick A: 1. Signal level meters vary between devices. So the levels indicated by different devices connected to the same aerial may show different levels. If they were more accurate then receivers would be more expensive as they would have to have more accurate components in!
An attenuator will reduce the level of the signals and will rectify the issue if it is caused by too high a signal level.
2. The level of the signal coming out of the aerial cable is relative to the strength of the signal in the air where your aerial is as well as the sensitivity of the aerial.
You have said that the problem seems to have arisen since the power increase of the three Commercial multiplexes from Sudbury last month. Each multiplex is a single signal which carries multiple services. For example, one carries all BBC standard definition services (BBC One, BBC Two, BBC Three etc).
It is not necessarily just the signal in question that is tuned to that can overwhelm a receiver. High power signals on nearby frequencies can do so as well. Since June you have more higher power signals on nearby frequencies.
A solution to a technical problem isn't necessarily clear cut. It is a case of making observations of what is happening and making a change which may seem the most likely. In this case, trying reducing the signal level would seem the most likely possible solution based on what we know. It is also the case that its cost is low.
You may be able to crudely attenuate the signal (reduce its level) by removing the aerial plug and holding it close to the socket (either at the wall socket or the back of the receiver).
Or at your location you may be able to use a set-top aerial. These being to test the theory that it may be too high a signal level.
If it is too high a signal level, then the fact that it works without difficulty sometimes could be explained by signal levels varying a little bit at different times. At certain times they become too high.
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Nick A: It may be worth checking that your receiver is tuned to the signals from Sudbury and that you are, unknowingly, watching the output from a neighbouring transmitter.
Signal strength screens usually give the UHF channel (frequency) that it is tuned to. There are six signals (multiplexes) from Sudbury:
PSB1 | BBC One | C44
PSB2 | ITV1 | C41
PSB3 | BBC One HD | C47 (if applicable)
COM4 | ITV3 | C58
COM5 | Pick TV | C60
COM6 | Yesterday | C56
The "C" numbers are UHF channel numbers.
I have listed one service carried on each multiplex. To identify which multiplex a particular service is carried on, see this page:
http://www.dmol.co.uk/mux….php
Looking at the predictor for your location, Sandy Heath and Crystal Palace are perhaps possibilities. If you find any of the PSBs tuned (incorrectly) to channels in the 20s, then a simple way around this is to run the automatic tuning scan with the aerial unplugged for the first 30% of the scan (or until it gets past C30).
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Tuesday 10 July 2012 6:16PM
Brian Norris: It might be worth discounting the LoftBox as being the cause, possibly through over-amplification. If there is a variable control, then try turning it down.
See Freeview signals: too much of a good thing is bad for you | ukfree.tv - 10 years of independent, free digital TV advice
The PSBs are at higher power than the COMs from Belmont.
The "DM Log" and "Log 40" are different aerials.