All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Gordon Elliott: Waltham broadcasts ITV Central (East) and BBC East Midlands so I am a little puzzled. If you are watching ITV Anglia with your aerial directed to Waltham then you must be receiving it off-beam which explains the poor signal.
Go to ITV and bring up the signal strength screen. It should tell you which UHF channel it is tuned to, which will allow you to identify whether you are tuned to Waltham or not.
Waltham is C54, King's Lynn is C46 and Tacolneston is C59.
Due to the terrain the north of Norfolk, along The Wash, does not get good reception of Tacolneston which is why there are dotted relays. However, there is quite good reception of Belmont, probably due to the flat Lincolnshire terrain.
In the days of four-channel analogue, King's Lynn relayed BBC One and ITV1 only. This was, so the powers that be said, the "correct" region for Belmont viewers. What it meant in practice is that two aerials were required: Belmont for BBC Two and Channel 4 and King's Lynn for BBC One and ITV1.
Following the switchover, King's Lynn carries all PSB (Public Service Broadcaster) channels. However, like over 1,000 similar small relays, it doesn't carry the COMs. So viewers may still wish to use the multiple aerial approach.
However, and here comes the but, it isn't as simple as in the days of analogue.
For a two-aerial diplexer you need to decide which channel to "split" at:
Online TV Splitters, Amps & Diplexers sales
ITV and C4 from Belmont were 28 and 32 and King's Lynn was 39 and 52 hence a diplexer that split and 36 would work.
Unfortunately the COM channels from Belmont or 30, 53 and 60 which is why I said in an earlier posting that two Belmont aerials would be needed and two diplexers, unless you do without C30.
Today, King's Lynn uses 43, 46 and 49. Use two aerials and a C38 diplexer and a C51 diplexer.
Feed the Belmont (53 and 60) aerial into the C51 diplexer (>C51 input) and the King's Lynn aerial into the other input. Then feed the output of that diplexer into the >38 input of the other diplexer and the other Belmont aerial into the other input of that diplexer.
I'm not a professional - I do wonder if it might be OK to use a single Belmont aerial with a splitter to give you two Belmont feeds.
There is a warning: if, or maybe when, the powers that be decide the channels are to change again, such as if they decide to sell off more spectrum for 4G mobile, then you "may" have to change it again.
If you're thinking that you can use Waltham's COMs instead, then you will have the same issue as they are 29, 56 and 57. And Sandy Heath's are 48, 51 and 52, so a C51 diplexer will be no good.
One other thing, the EPG data for all services is carried on all channels. This can sometimes cause difficulty for recorders when receiving from two different transmitter groups (presumably where the EPG data isn't shared). However, Digital UK says of King's Lynn "The Kings Lynn transmitter provides additional regional services to viewers of Belmont." which suggests that this might not be an issue.
For that reason, the Belmont/King's Lynn approach would probably be preferred, if the full service from Tacolneston isn't possible. Tacolneston got a taller mast for switchover so its coverage has increased.
For information on aerials, see ATV's site:
Aerials, TV Aerial and Digital Aerial
If you have an amplifier, I would certainly see if turning it down helps.
A higher gain aerial isn't necessarily a solution. There is a trade-off where the greater gain reduces the acceptance angle (narrow "beam"). This is because gain is simply at the expense of greater "loss" in other directions.
With digital reception you need good quality (digits intact). You can make a weak good quality signal bigger with an amplifier. You can't make a poor quality strong signal better.
Thus, if quality of the signal across the narrower angle isn't as good as the average quality of the signal over the wider angle, you will end up with a poorer signal. That is the theory as I understand it - I hope that it helps picture what's going on.
Another question: How well could you receive digital prior to switchover?
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Rob Armstrong: No, the PSB-only transmitters are likely to say like that. See:
Londonderry (Northern Ireland) digital TV transmitter | ukfree.tv - 10 years of independent, free digital TV advice
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Tea: Which channels are you missing? Is it the COMs (it usually is the case).
See here and identify which multiplex(es) you are missing (PSB1, PSB2, PSB3, COM4, COM5, COM6):
DTG :: DTT Services by Multiplex
For the COM channels from Lark Stone you may have to replace your aerial with a wideband (or Group K) one, if you haven't already done so.
Or, instead of Lark Stone, you might be able to use Sutton Coldfield for all channels.
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Mike: See:
mb21 - The Transmission Gallery
It's at the back of the garages on Southmead Crescent.
OS Grid Ref: ST44460922
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Gordon Elliott: Some receivers give you a choice of "network" (region) where signals from more than one are found during the scan.
In the UK, the networks identify themselves by their principal service areas, rather than transmitter names. This is because if they broadcast their names, relays would carry the same names as their parents. For example, King's Lynn would say "Tacolneston".
So, as you have gathered, the ITV1 Anglia you have been receiving is poor because your aerial is perpendicular and opposite polarisation to what it should be for the signal in question.
As King's Lynn only broadcasts PSBs then your Panasonic has to go with what it can get for other channels (COMs); Waltham being the best because that's what the aerial faces, I assume, and this is why they are identified as "East Midlands".
The fact that you are receiving King's Lynn with the aerial pointed as it is could be an indication that you are in an excellent signal area for it. If you are indeed in a good signal area for KL, then use a log periodic aerial (DM Log or Log 40). As you have realised, KL, like most small relays in this country, radiates vertically-polarised signals so aerials need to be vertical. Aerials can be fitted either horizontally and vertically.
I am not so sure that reception of Belmont might be as easy as you might be thinking. The bearings for Waltham and Belmont are almost west and north west respectively. For both there is high-ground obstructing line-of-sight on which there is vegetation to which you only live a few hundred metres away. The drop after the high-ground down which you reside is, I believe having consulted a terrain-plotter, greater for Belmont than for Waltham.
I used Megalithia to plot the terrain:
Terrain - shows radio profile between two UK sites to optimise you DTT, Freeview, DAB or analogue TV reception
The "base" station is your location which is TF678337. To use it, select the region and then the transmitter. Belmont is under "Borders, Northern England" and Waltham is under "Midlands, Eastern England". Having given a plot of the terrain you can click the link to see a line between you and the transmitter. This allows you to view satellite images to see what's on the ground.
Think about what it is that you are trying to achieve. Ideally there should be line-of-sight to the transmitting station because signals travel in straight lines. However, it is often the case that there is no direct path from the transmitter and so reception often relies on refraction to some degree or another.
Consider driving towards the brow of an upwards slope at night with headlights come towards you. As the approaching car gets closer, the "mass" of light above the brow becomes greater, although there no direct line-of-sight. Now imagine if on the brow there was something such as vegetation. This would then affect (cause shadows) the light that is coming over the brow.
The effect of the trees on the brow could be likened to that of the vegetation on approaching car headlights. The signal can be corrupted due to effects of the refraction, and so on, of the trees. The effect of trees can vary by time such as when they are wet, when there is wind blowing them about and when they have leaves on.
With digital reception there are two factors: quality (digits intact and not corrupted) and magnitude (strength). Providing that the strength is above the threshold which your receiver needs to resolve a picture (and quality is at its optimum) then you will have a picture that is as good as it gets.
A signal that is of good quality but isn't of sufficient strength to resolve a picture can be made bigger using an amplifier. A signal which is of sufficient strength but not of sufficient quality (digits damaged) cannot be improved (re-built) using an amplifier or any other device.
See here for more of an explanation:
A.T.V (Aerials And Television) TV Aerial, DAB Aerial, FM Aerial. ampsandsplitters.html#ampbasics">Television Aerial Boosters / Amplifiers, Splitters, Diplexers & Triplexers
An aerial with a narrower acceptance angle therefore has a narrower field of view. If the average *quality* of the signal across that narrower field is less than the average quality of the signal across a wider field then it stands to reason that the wider angle will give you the better quality signal, even though the gain of the aerial is probably less, but you can amplify it to make it bigger (if needs be).
This isn't to say that one will work and the other won't; it is more to give you an idea that going for greater gain isn't always the better choice.
Also, a wideband yagi aerial has less gain on lower channels, of which you will be using to pick up COM4 from Belmont on C30 or COM4 from Waltham on C29. See here for examples:
A.T.V (Aerials And Television) TV Aerial, DAB Aerial, FM Aerial. gaincurves.html#WidebandCurves">Gain (curves), Again
The less gain you have the less directional the aerial is. So a Standard 1 wideband aerial (you need a wideband for Belmont or Waltham) would have less gain on C29 and C30 than those in the 50s and 60s. This begs a question: if it is sufficient to pick up C29/C30, then why the need for higher gain on the higher channels? Or to look at it another way, it may work for 50s and 60s but not 29/30.
Again, obviously, we can't say either way whether it will or will not work - it's a case that higher gain isn't always better.
You asked about combining the feeds from aerials. Diplexers contain filters so that on any one UHF channel only one aerial is being "used". For example, if you use a C51 diplexer, one aerial will be used if you tune to C39 whereas the other aerial will be used when you tune to C53.
There is no saying that using a splitter in reverse to combine the two feeds won't work. But it may not be as effective or may give unpredictable results.
The difficulty you have, as I outlined in my previous posting, is that diplexers have a "split" point where one aerial is used for channels above and the other for channels below. The COM4s from Waltham and Belmont are below KL's but COM5 and COM6 of both are above it.
Presumably you have established that you get good reception of Waltham's COMs. You could re-orientate your current aerial to Belmont and see what you get. With digital reception it is best to give it time (days maybe) because, as I said, it could be affected at different times. If you get good reception from Belmont then install a log aerial on KL.
You will obviously need to decide whether you are going to chance it and see if a splitter in reverse will combine the two aerials. If it doesn't work then you may wish to have a Plan B. This might be proper diplexers with either a second Belmont aerial or splitter on the Belmont aerial to feed the lower and upper diplexer inputs. Of course, there will be losses associated with feeding the signals through the splitter and diplexers which might require mitigation with an amplifier.
If Belmont isn't good enough then you could always move your horizontal aerial back to Waltham. Any diplexers/splitters installed will be the same for Waltham as Belmont so these hopefully won't require adjustment.
Or you may find that a log is better for Belmont (possibly with some degree of amplification) and use the current aerial on KL. Of course you would have to swap the feeds if you are using diplexers.
Logs are native wideband with flat gain curves, unlike yagis whose curves go down on lower channels (see gain curves link above for examples).
As I say, see ATV's site for more information: A.T.V (Aerials And Television) TV Aerial, DAB Aerial, FM Aerial. They may be able to give you guidance on the best way forward. The spanner in the works being that COM4 is below KL's channels irrespective of which transmitter you use. The DM Log and Log 40 are the names that ATV gives to the aerials it stocks. These are the Blake DML26WB and Vision 40 respectively.
I'm not a professional and am just giving you the theory as I understand it.
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Lynn Steenson: The Digital UK predictor essentially provides a statistic on the likelihood of success. COM6 is "good" but the other two are considered "variable". I imagine that this is more down to the way in which it calculates the likelihood of interference from other transmitters that use the same channel. I wouldn't be too concerned about that.
The Fringe P1290 is a power supply for an amplifier and not an amplifier. The amplifier is probably on the roof or near to the aerial. Turning the power of to the amplifier will likely result in no signal coming out.
You appear not to have many more options left without getting into it deeper. Removing the amplifier, or turning it down (if possible), is probably the next thing that needs trying.
The lower power COMs will affect some fringe viewers - that is those who can "only just" pick up the PSBs. This would appear not to be an issue for you. You may have line-of-sight or not far off which is why I'm thinking that the amplifier isn't necessary, or at least at the current magnitude.
An attenuator on the aerial lead may reduce the signal strength sufficiently if you can't get to remove the amp or reduce its level. An attenuator reduces the signal level which is the opposite of an amplifier. Therefore an attenuator would be acting to cancel out some of the amplification of the amp.
Various ones are available. Here is one such example that is variable:
TV Aerial Attenuator Variable 0-20Db Freeview Digital | eBay
Try to reduce the signal strength (to say 75 or 80%) and see if the quality of the COMs increases and they become available to you.
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Gordon Elliott: Some of those links have gone awry.
Gain curves:
Gain (curves), Again
Diplexers:
Online TV Splitters, Amps & Diplexers sales
And an explanation of why high-gain wideband aerials aren't good on Group A channels:
Rowridge Transmitter
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chris: It all depends on whether you can receive the COM channels from another transmitter and that they are of sufficient quality as those from Strabane are now.
The only possible transmitter, if any, that is likely to give you all channels is Limavady.
Let's suppose that you can receive all channels from Limavady, with the appropriate aerial. Therefore, it may have been the case that you could receive analogue from Limavady before but your installer decided that Strabane was the better signal and easier to receive. At that time both transmitters provided equal service to your location.
Today, "if" Limavady is available to you, it might provide you with the full complement of channels rather than the limited choice of Strabane.
Only an aerial installer can tell you if you have any chance of picking up all channels from Limavady. If not, then you will have to stick with Strabane.
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Gordon Elliott: By connecting two aerials together using a splitter in reverse (and without any filtering) you are, in effect, creating another aerial. You KL aerial will be acting to pick up the Belmont channels and vice versa. When you combine them you will get the sum coming down your aerial lead.
If they are out of phase which is one is on its "up" and the other is on its "down" then they will cancel out and you will be left with nothing. Adjusting the distance between the aerials may help with this. This is because the signals are an alternating waveform as they travel and moving one aerial will adjust whereabouts in the waveform it picks up *relative* to the other.
As I said previously, connecting two aerials using a splitter in reverse might create an unpredictable mess.
So this got me thinking. How else might you achieve your goal?
Filters are available that pass channel groups and these are known as "band-pass" filters. If you fit a Group B one to your KL aerial this will give you 34 to 53. This will prevent 30 and 60 although 53 will go through. As such, maybe this might work better with Waltham's COMs as they are 29, 56 and 57.
You could they either combine (with a splitter in reverse) the output of your filtered KL aerial with that of the unfiltered Waltham one. This would mean that for 29, 56 and 57 you would be using only your Waltham aerial although for KL channels both aerials would be picking up. You may be lucky in that the KL signal is so strong that the Heath Robinson of two aerials might get you by - albeit that you might have to experiment with distance between the two.
Failing that, you would have to see how you might be able to filter 43, 46 and 49 from your Waltham aerial (before it is fed into the reverse splitter). Oh, and on 1st May this year 49 from KL will move to 40.
A three-channel notch filter would allow you to do this. You will need to change one of the notches at the beginning of May. Notch filters are few and far between and their price might mean that another method might be cheaper.
The only possible fly in the ointment with this is that the powers that be might allow new services to start in the range 34 to 37; these probably being from main stations only:
Ten more HD channels on two new Freeview HD multiplexes on air from 2014-18 | Freeview news | ukfree.tv - 10 years of independent, free digital TV advice
You would then need to filter out relevant channels from your KL aerial....
As I say, I'm not a professional and this is just my understanding combined with thoughts of what you might do.
If you speak to the guys at ATV in Sheffield they may be able to offer you some suggestions. Making it as future-proof as possible will help reduce the likelihood of having to change it, maybe at cost, later.
As they say:
"We are more than willing to give advice to those actually purchasing from us.
Could those only seeking information please just use the information on this website, or ring an aerial installer local to them, or try calling reception advice, remember, they`re paid to advise you (unlike us)."
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Saturday 19 January 2013 5:46PM
Gordon Elliott: Your postings are on another page:
Freeview reception - all about aerials | Installing | ukfree.tv - 10 years of independent, free digital TV advice
In some cases you may find that you have to click on the "Page #" tab near the bottom of the page, because since you made your posting a new page has been started.