New Rooftop Aerial Needed

yorkie98

Again, it's horses for courses. In this area, most will have a group A aerial pointed at the Divis transmitter. All of the muxes are in band with the exception of mux C which is on UHF CH48 which is well outside of the range of a group A aerial. Mux D on CH34 is on the edge and can also suffer a little.

That said, this mux (Mux C) transmits at 3.0KW whereas most of the other muxes are at 2.3KW. This goes some way to compensate for the inefficency of the group A aerial at this frequency. Many have found that although this is noticably their weakest mux, the reception is still adequate and does not warrant an upgrade at this time. This is certainly the way it has worked out in my case.
Ideally I would change to a digitally benchmarked wideband aerial but for the time being, I see little or no need.

After DSO the power of these muxes is likely to increase to 10-20KW and mux C will be moved to UHF CH26 and mux D will be moved from CH34 to CH29, therefore, existing group A aerials will work fine for years to come. This scenario is likely to be true across most of the UK but in the run up to DSO there will be a lot of people having their aerials upgraded for the "here and now" which would be fine after DSO.

As I mentioned before, my advice to anyone is to try the box first and see if it works. If the reception is not satisfactory, then arrange an aerial upgrade but expect to pay upwards of £150 for a top to bottom install.
If you can live with the reception (even it occasionally plays up) ride the storm til 2012 and the reception will improve massively once switchover is complete.

If you do want an aerial upgrade, get it done sooner rather than later as the closer we get to switchover date, the harder it will be to get an appointment, cowboys will set up and prices will be inflated due to demand.
Once switchover has happened tho, the sunshine will stop very quickly for installers once either everyone has upgraded or everyone who has not upgraded realises that their old aerial works fine.

yorkie98

cajef wrote: »

Thank you for a well written post that just goes to prove that there is no such thing as a digital aerial, there maybe digital approved aerials which may be made of slightly better materials.

As you have correctly pointed out, reception does depend on choosing the correct group and array for the location, alignment which is far more critical for digital reception, and quality of the materials used, quite often if the correct aerial has been installed originally than re-alignment and replacing co-axial cable can improve digital reception without the need to replace the complete installation, though aerial fitters would have you believe otherwise.

The question over what is and what is not a "digital" aerial could go on forever, especially as a digital benchmarked aerial should also in therory improve analog reception as well. These type of aerial were generally designed to meet the stringent requirements of digital reception and thus to call them a "digital" aerial, in my opinion, is neither unfair nor misleading.

If you were to offer someone a "Sky" dish, are you misleading them as it can pick up services other than Sky? It's much easier than offerning a "generic parabolic antenna with dual KU band, dual polarity LNB".

I certainly don't think it's fair to state that if an installer offers a "digital" aerial then he is trying to rip you off, as you said further up the thread.
You certainly wouldnt be pleased if you asked to have your digital reception improved and the installer bunged up a standard contractor aerial (even if it was a wideband).
If he were to offer as a "digital aerial", an aerial which has not been benchmarked as a digital aerial then he is ripping you off for sure but the benchmarking scheme is in place to assure the public that they are getting an aerial which is fit for purpose and to prevent an installer branding any product he fancies as "digital".
On the strength of this I think it is quite reasonable to use the term "digital aerial" without being accused of trying to scam the public.

maveli

I bought this from Maplin. http://www.maplin.co.uk/Module.aspx?ModuleNo=22523&C=Maplin&U=SearchTop&T=ariel&doy=24m7

Went to to loft and placed it there, cut the existing wire from the roof top antena, connected it to the new one in loft. that's all you need to do. there is no need this to be on roof top. I am around 10 miles away from the nearset digital transmitter

yorkie98

maveli wrote: »

I bought this from Maplin. http://www.maplin.co.uk/Module.aspx?ModuleNo=22523&C=Maplin&U=SearchTop&T=ariel&doy=24m7

Went to to loft and placed it there, cut the existing wire from the roof top antena, connected it to the new one in loft. that's all you need to do. there is no need this to be on roof top. I am around 10 miles away from the nearset digital transmitter

If you are only 10 miles from your transmitter and you are not in a significant dip, then you should have good line of site to the transmitter and loft reception should be good.
If your signal strenth is good enough then the loft is fine although you can sometimes leave yourself a little more vulnerable to impulse interference from the house electrics. You are however a lot less vulneralble to lightning.

This solution is a valid one for yourself but would not be suitable for those in moderate or fringe reception areas. For the vast majority, a roof aerial will be needed. Transmitter planning is worked out assuming roof mounted aerials.

Also some lofts are not suitable for tv reception due to the insulation materials used. Most modern dwellings are built with double foiled foam block between the roof rafters and this kills most signals dead.

cajef

yorkie98 wrote: »

If you were to offer someone a "Sky" dish, are you misleading them as it can pick up services other than Sky?

You certainly wouldnt be pleased if you asked to have your digital reception improved and the installer bunged up a standard contractor aerial (even if it was a wideband).

I would not offer someone a SKY dish, another incorrect term, it is a satellite dish.

I happen to live in a fringe area and had poor digital reception, I was informed by three reputable aerial installers that the only way I could improve it was by fitting a so called digital aerial.

Funny how with a standard contractor aerial that is ten years old, after fitting new coax and re-aligning the aerial I now manage to have perfect digital reception on all channels, but hey what do I know I was only an electronics engineer for thirty years, so what is the technical difference between a standard contractor aerial and a so called digital aerial, give me some facts and specification, not just aerial installers waffle that digital aerials are digital approved or digital suitable.

yorkie98

If you could tell me which transmitter you are on, I could probably give more specific reasons why your contractor aerial works. I see you are in East Anglia, I used to live in Suffolk. If you are on Sandy Heath or Tacloneston then a contractor aerial will be OK as all muxes are in or close to band. I'm guessing you aren't on Sudbury as that has several out of band muxes and the ITV mux is an absolute pain at the best of times. A normal group B aerial is simply not good enough in most cases for Sudbury.
Replacing your cable could have also made a significant difference, especially if it had degraded or was suffering from water ingress. Even changing 10 meters of old "low loss" cable for CT100 could have gained you over 3dB which is equivalent the transmitters' power being doubled.
If I had been called to your house I would have identified possible problems before replacing your aerial unless you specificly asked me to just junk the old system and fit new from top to bottom.

The most significant difference between a benchmarked aerial and a contractors aerial is the presence of a 300 to 75 Ohm balun to correctly match the aerial and cable impedences, as opposed to the coax being simply screwed into either side of the dipole. The connection is usually made via a Type F connector instead of bare cable into terminals. This Balun also isolates the feeder from the aerial metalwork and significantly reduces the pickup of impulse noise (car/motorcycle ignition etc). There are also requirements for the response curve across the UHF band to be within certain limits and for the forward gain to attain certain figures.

For full information look here: http://www.dtg.org.uk/publications/books/cai_dtg_bmrk_aerials.pdf

As I have stated before, not everyone will need a new aerial (or indeed a "digital" aerial. For many, their current aerial will suffice, mine does in spite of one of the muxes being on CH48 and my aerial being a group A. For those that do need or require an improved performance, there is a system in place to test aerials and certify them as fit for the specific purpose of improving digital reception.
There will be a minority of people who need to make every tweak going to get good digital reception at present low transmission levels. They will need the best digitally benchmarked aerial and highest quality downlead and possibly screened amplifiers to get a reception and prevent impulse noise. Impulse noise is the biggest threat to digital reception as it causes huge chunks of data to be lost and often results in a few seconds of picture breakup or loss.

As for credentials, I haven't been an electronics engineer for 30 years as i'm not old enough but I had a total of 8 years experience (2 seperate occasions) in the aerial and communal system instalation trade and have first hand experience of the many problems and pitfalls accociated with TV reception, both digital and analogue. I worked for Agilent Technologies as an electronics engineer for 7 years. I'm now a Broadcast engineer so I have experience of both trying to receive signals and getting them out to people, and the electronics involved inbetween so I'm not just a roof monkey, I'm an over-qualified ex-roof monkey.

Being an electronics engineer does not give much insight into the practicalties of signal reception unless you have had extensive experience in this specific field. If you had, you would know the difference between balanced and unbalanced aerial systems and the benefits of a balanced system. You wouldn't need to question the merits of them as you would already know what they are.
If only I had a pound for every "electronics engineer" who has stated that trees don't cause bad TV reception, and other such myths, I could have retired years ago.

Don't get me wrong, i'm not saying there aren't rogue aerial installers out there, I've come across plenty in my time some who'd love to rob your granny for all she's worth and sleep perfectly well.
I on the other hand, was a good installer, in fact I was a very good installer as I always gave the best advice and made my clients aware of all the options before going ahead and never ripped people off. I'd always try my hardest to get the best reception possible, always used the correct test equipment and never had a "that will do" mentality.
That's why I'm on a forum like this giving my advice for free as an ex-installer. I hate people geting ripped off but I dislike bad advice almost as much because this can end up costing people money.

cajef

yorkie98 wrote: »

Being an electronics engineer does not give much insight into the practicalties of signal reception unless you have had extensive experience in this specific field. If you had, you would know the difference between balanced and unbalanced aerial systems and the benefits of a balanced system.

If only I had a pound for every "electronics engineer" who has stated that trees don't cause bad TV reception, and other such myths, I could have retired years ago.

Interesting debate, and I agree with you entirely that the materials and quality of installation are the main factors for good reception, but I have still to remain convinced as to what defines such a thing as a digital aerial, if most people were to purchase a 'digital aerial' expecting it to cure their reception problems without the necessary installation knowhow they would be disappointed, I think we will have to agree to differ on this point.

As a matter of interest, I worked for an international communications company and was involved in the development of slotted waveguide for radar, transmission and reception at all frequencies, from LF arrays to microwave and satellite antenna, so I do have a little knowledge of aerial theory, though I will admit to it being a little rusty now.:D

yorkie98

cajef wrote: »

Interesting debate, and I agree with you entirely that the materials and quality of installation are the main factors for good reception, but I have still to remain convinced as to what defines such a thing as a digital aerial, if most people were to purchase a 'digital aerial' expecting it to cure their reception problems without the necessary installation knowhow they would be disappointed, I think we will have to agree to differ on this point.

As a matter of interest, I worked for an international communications company and was involved in the development of slotted waveguide for radar, transmission and reception at all frequencies, from LF arrays to microwave and satellite antenna, so I do have a little knowledge of aerial theory, though I will admit to it being a little rusty now.:D

What defines a "digital" (benchmarked) aerial is set out in explicit technical terms in the pdf I linked to in a previous post.

It's absolutely right that simply purchasing a "digital" aerial will not neccesarily cure problems for people, often poor digital reception is due to a number of factors which all need to be addressed. Ideally all installation work would be carried out by professionals to obtain the best possible results but those who wish to try DIY need to be able to obtain the correct materials also (i.e, a benchmarked aerial).

Over the years, I would very often be called out to a misguided DIYer who takes you into the loft and says, "I bought this aerial from B&Q/Argos but it doesn't work", only to find that its pointing the wrong way or the coax was twisted together or other such similar DIY disasters.

It remains a fact though that for optimum digital reception, whether, you are DIYing or having the work done professionaly, a benchmarked aerial should be used as a matter of course but as you rightly state, this only part of the puzzle. Correct sighting/alignment, quality of downlead, local interference, impulse noise, screening and many more are also factors and an individual could suffer as a result of any one, or a number of these factors. There is no one-for-all solution but using a benchmarked aerial is a big step in the right direction.

As I stated before, this is all only relevant in the current pre-DSO landscape.
When DSO is completed, this will all change and most of the reception difficulties experienced currently by many people will disappear almost overnight when the TX powers go up. Those currently close to or under the good reception threshold will suddenly be getting excellent reception on 30 year old rusty systems, or set-top aerials which wouldn't have stood a chance in the current environment.