Freeview reception - all about aerials
Brian Butterworth published on UK Free TV Updated 8th January 2014.
Your ability of receive all the Freeview transmissions depends on the suitability of aerial
- the design style,
- the "group", and
- its physical location.
Standard type - Yagi aerial
The standard type of TV aerial is known as the Yagi aerial. It is mounted on a pole, and consists of a rod with a reflector (shown green) at the back and many spiky elements (in grey) at the front. The connecting cable connects to the element nearest the reflector, known as the driver (shown in blue).
These Yagi aerials are directional and so pick up signals best from a transmitter that the rod points towards. The more elements the aerial has, the better it picks up a signal and becomes more directional.
A standard-type aerial is all that is required for digital TV reception in most places. These antennae have between 10 and 18 elements and a single reflector. These are recommended for new installations for good digital television reception, but will more often than not function perfectly in good reception areas.
Typically these aerials are designed to receive only some transmission frequencies - see "groups" below.
High Gain aerials
These aerials are designed for poor digital reception areas, and have two reflectors. For maximum signal strength, some digital high gain aerials have up to 100 elements. Since the switchover to digital-only transmissions back in October 2012, most UK households now have good quality digital TV signals.
A more expensive aerial is only required where the signal strength is low, but can often provide the whole Freeview reception where it might otherwise be impossible.
The CAI (that represents aerial installers) has four standards for digital TV aerials. The highest standard "1" is for homes on the fringes of coverage areas, intermediate standard "2" is suitable for use within the coverage area; minimum standard "3" is for good coverage conditions.
These aerials can be either wideband, or receive only selected frequencies - see "groups" below.
Grid
You may haved used a 'Grid aerial' for analogue reception, but as they are generally unsuitable for Freeview reception, they have now generally been replaced by the Yagi type. However in some places a Grid aerial installation may work for Freeview: otherwise replace with a standard Yagi aerial.
Indoor
Indoor aerials are generally not suitable for Freeview reception. In areas of good signal strength it is often possible to receive some transmissions. Even where an aerial works, people often find that may get interruptions to their viewing (or recording).Loft mounted
Loft mounted arrivals are not generally recommended for Freeview reception, as the roof tiles and plumbing will degrade the signal. Some compensation for this loss of signal can be made by using satellite-grade cable to connect the set top box to the aerial.Positioning
The best position for a TV aerial is mounted outdoors, as high from the ground as possible, pointing directly at the transmitter. The signal can be blocked by hills and tall buildings. It should be positioned away from any other aerials.Horizontal or vertical?
The transmitter will either use vertical mode which requires the elements of your aerial to be up-down, or horizontal mode which requires them to be level with the ground.Groups
Both analogue and digital television is transmitted the same group of transmission frequencies (known as channel 21 through to 60). A coloured marking on the aerial shows the group.
To create the best possible analogue picture, TV transmissions from adjacent transmitters have been designated to several different groups of frequencies. By using an aerial that receives only the channels in the correct group, the analogue picture can be kept free from interference.
To receive Freeview transmissions from the same transmitter it has been sometimes necessary to use frequencies that are not part of the transmitter's normal group. When this has occurred, the aerial will need to be replaced with a "wideband" aerial (also known as group W) - one that covers every group.
As Ofcom is planning to move the TV frequencies again - perhaps as soon as 2018 - it may be wise to use a wideband aerial if you can to ensure you can keep viewing Freeview for many years to come.
Help with Television sets?
Sunday, 20 January 2013
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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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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Monday, 21 January 2013
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)."
Contact Us
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Gordon Elliott: Or, of course, you could have two aerials, keep the feeds separate and feed them each into a different receiver.
For example, feed the full complement of channels from Waltham or Belmont into your PVR and TV. Have a set-top box receiver for KL which you use when regional programming is being broadcast which these days is the local news and one or two regional programmes.
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Gordon Elliott11:45 AM
King's Lynn
Dear Dave Lindsay
Many thanks for your replies.
It will take me some time to get my head around that lot, so it may be a day or so before I reply.
Again, many thanks for pointing out all the pitfalls. It is obviously not straight forward and I need to give it some deep thought.
Best regards
Gordon Elliott
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Gordon's: mapG's Freeview map terrainG's terrain plot wavesG's frequency data G's Freeview Detailed Coverage
Gordon Elliott: No problem.
Here is another explanation to summarise what you're trying to do:
If you combine the two aerials (using a splitter in reverse) you will get the sum of the two signals. That is, when you are receiving from Belmont on C30, the KL aerial will also be picking up that channel. You will get the sum do your aerial lead.
Therefore the objective is to prevent (by filtering out) the channels of one transmitter being picked up by the other's aerial. So you are trying to stop the KL aerial picking up 30, 53 and 60; and you wish to stop the Belmont aerial picking up 43, 46 and 49 (to change to 40). If you can achieve this using filters, then you can combine the result.
The "future-proof" thing means that Belmont "might" be broadcasting on 33 and 35. There was talk of using 36 at one time, but that doesn't appear on the cards of these proposed HD muxes.
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Gordon Elliott4:13 PM
King's Lynn
Dear Dave Langley.
OK, I have managed to get my head around that lot by mapping out on a spreadsheet the Waltham and KL Channels and their corresponding broadcast frequencies.
It would appear that it is a question of whether just using a splitter acting as a combiner would give just the discrete sum of the 2 aerials or whether there would be some interference injected due to reflections and carrier interactions.
As far as I can make out, the two transmitters in question do not broadcast and channels which use duplicate frequencies, therefore in theory one should just be able to combine them. If that does not work then there is always the option to insert passband diplexers as you suggested, which I am fairly certain would have the desired effect.
As to the future proofing, I am now 73 years old (male ) and I will probably not be around to worry about any of it for much longer, but I like to keep my brain active.
I used be an electronics service engineer, but in a totally different subject field and my TV transmitter knowledge is somewhat limited. If I can get someone to point me in the right direction however, such as you have, then I can usually get to the end product.
Once again, many many thanks for your detailed assistance. I will let you know sometime in the future what the outcome was.
Best regards
Gordon Elliott
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Gordon's: mapG's Freeview map terrainG's terrain plot wavesG's frequency data G's Freeview Detailed Coverage
Tuesday, 22 January 2013
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Gordon Elliott9:15 AM
King's Lynn
Dear Dave Lindsay
Further to my post of yesterday and after further thought, I see now what you meant about perhaps the KL signal being able to drown out the Belmont/Waltham transmitter(s) because in theory two aerials would be receiving the signals from all three transmitters to some extent.
However, with the KL Tx being vertically polarised I would hope that the pickup on that aerial from Waltham/Belmont Txs would be absolutely minimal.
Therefore I think that just using as combiner would probably stand a good chance of working.
Best regards
Gordon Elliott
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Gordon's: mapG's Freeview map terrainG's terrain plot wavesG's frequency data G's Freeview Detailed Coverage
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David10:18 AM
Coleford
Hello, I have just moved to GL16 8LJ. I want to fit a loft aerial for the Mendip West transmitter. I believe I need an aerial for Group E/W but am confused what these letters mean. Does the W bit mean wideband and if so do I need it because it seems that wideband can "let in" lots of interference from other channels. I have an ordinary Tesco flat screen digital tv. The existing external yagi aerial is horizontal, seven elements and six element reflector.
Your advice would be most welcome. Thanks a lot.
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David's: mapD's Freeview map terrainD's terrain plot wavesD's frequency data D's Freeview Detailed Coverage
David: See:
Mendip Transmitter
If this is a second TV can you run it off the roof-top aerial as well?
According to the Megalithia terrain plotter, you would appear to have line-of-sight to the top of the Mendip mast which is 36 miles away.
There is always the possiblity that channels from Mendip might change in future (due to the 4G clearance) and the ned HD services that are likely to use channels 31 to 37. As such, I suggest that you look at a Group E or wideband aerial.
How effective it will be in the loft obviously depends on how much or how little the roof blocks the signal.
Having an aerial that is sensitive across more of the band (e.g. wideband) doesn't have any effect on what you're receiving. Your receiver is tuned to one particular channel at any one time so other signals don't affect it.
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