NEWSLETTER DECEMBER 2014 Editor Ron Everitt Contact on or

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1 NEWSLETTER DECEMBER 2014 Editor Ron Everitt Contact on or The Meeting on November 19th was attended by 31 members and guests for a talk by David Goddard and David Bradshaw on the development of Digital Radio and Television David Goddard started by summarizing his previous talk on the introduction of digital television Analogue television was started with Band 1 (VHF) 41 to 68 MHz Channels Lines for BBC1. This was supplemented with Band III 176 to 215 MHz giving Channels 6 to 13 when ITV started, again with 405 lines. The BBC used these as well in some parts of the country. Bands I and III were discontinued in 1985 with the closure of the 405 line standard. Bands IV and V (UHF) 470 to 854 MHz were used for the 625 line services on channels 21 to 34 and 39 to 68 for BBC2 from April 1964 and BBC1 and ITV from November 1969 Channel 4 started in November 1982 and Channels 35 to 38 provided Channel 5 from March 1997 Digital TV used Bands IV and V 470 to 854 MHz on Channels 21 to 69 As a preparation for 4G telephone services channels were cleared and are no longer used for television services. Unlike analogue transmissions digital Radio and TV services are carried on multiplexes providing multiple choice. Digital transmissions started on the 15th November 1998 as the OnDigital service and became Freeview from 30th October The Switch to Digital was completed in October 2012 and this resulted in the complete closure of the analogue services. Today we have Freeview, Sky (both subscription and free), Freesat and Internet services providing digital television. Currently we have 8 multiplexes providing television across much of the country (although as little as three in some parts). Currently we have 8 multiplexes providing television across the country. PSB 1(or BBC A) provides the BBC transmissions SD PSB 2 (or Digital 3 & 4) provides ITV, C4 and Five SD PSB 3 (or BBC B) provides HD television COM 4 (or SDN) Commercial services SD COM 5 (or Arqiva A) Commercial services SD COM 6 (or Arqiva B) Commercial services SD COM 7 (or Arqiva C) Commercial services HD COM 8 (or Arqiva D) Commercialservices HD The alternatives to terrestrial TV are available from satellite and Internet systems. In some areas of the country where the main transmitters are unavailable the local repeaters only provide Freeview Lite which only provides the main TV channels. In these areas

2 the only alternatives are Satellite ot Internet services. Sky Television is subscription based and the digibox and dish are provided as part of the package. Freesat from Sky is free to use but you have to supply your own digibox and dish. Freesat is provided by the BBC and ITV and is also free apart from the cost of the digibox and dish Internet connection is regarded as the future for television and allows a much wider choice of programs. It also allows the user to choose when to watch a program without the need to record. David continued by describing the future of digital Radio. Analogue radio has been operating since the early years of the last century. Starting with long (153 to 279 KHz and medium wave 531 to 1620 KHz. These are still in use but may not survive for much longer. Many throughout Europe have already closed. HF or SW (2310 to KHz are still used but have been largely superceded by satellite and local retransmission Band II (VHF/FM ) 87.5 to 108 MHz are expected to be replaced by DAB Babd III (VHF) 176 to 215 MHz was formerly used for TV in the UK and has now been allocated to DAB L-Band 1452 to 1492 is the DAB standard in some parts of the world but has a low takeup Digital radio research started in 1981 and was originally known as Eureka 147. The BBC started transmissions in 1995 using the former Band III VHF TV frequencies. Since Europe still uses Band III for television in some cases it did not follow the British example. The original DAB specification is now regarded as primitive and DAB+ was adopted by the World DMB forum but so far Britain has not decided whether to use it. As the two systems are not compatible we would need either to establish parallel systems for a period or use a sudden death switchover if we do decide to use the better DAB+ system. Apparently the current radios being marketed will operate with both systems but the earlier British DAB radios would have to be written off if we switch. 2

3 3 Radio Multiplexes TV multiplex Listing David made the comment that commercial stations were not generally in favour of running DAB+ along with DAB because of the extra cost but this might not be a problem if the sudden death approach was used. Trials of DAB+ have started in some parts of the country but the Government has not made any commitment apart from saying that FM will be replace by DAB some time. David Bradshaw the took over to talk about the future development of Digital broadcasting Possible areas for improvement were the use of Stereoscopic T 4K Ultra high definition TV Connected TV and Smart TV Much of the advertising of 3D TV is misleading since it creates an impression of depth but only behind the screen and not in front. The impression of depth is made from slightly different images being seen by each eye

4 4 Anag lyph process The two images corresponding to the view seen by each eye are combined either with a different colour or by polarised light and transmitted as a single image Seperating the images Some projection systems use red and cyan images with colour filters in the glasses or polarisation TV systems use polarisation to separate the left and right images. The 3D illusion is created in the receiver but there is more than one way to present the images on the TV Display This may be Pixel by pixel Alternate pixels corresponding to the nleft and right images are interleaved in the display.

5 5 TV line by line Alternate scan lines show the left and right eye images Polarising film filters on the screen and passive glasses separate the images Left eye image Right eye Image TV field by field Alternate fields show the images fot the left and right eyes Images can be separatet by active polarising glasses The glasses For the passive system the TV screen is coated so that light from alternate scan lines is polarised differently. The two imagesare interlaced on the screen, one for each eye. Polarisation in the lenses matches the coating on the screen ensuring that the proper image is delivered to each eye. This provides a simple and inexpensive system that relies on basic optics but effectively halves the resolution delivered to each eye. Passive 3D is currently only used on some LCD and LED TV models and is not available on plasma TV s. Because it relies on a screen coating it may never be available for projectors. The Glasses Rather than interleaving two half resolution images in space, it interleaves two full resolution images in time. The TV showa images for the right and left eyes alternately, while the glasses use electronic shutters synchronised to the TV to ensure that each eye sees a different image. The only real technological requirement for the TV is that it is able to refresh the screen quickly enough to supply images for both eyes. Active 3D is the only form available on projection and plasma TV s as well as LCDE and LED models. 3D TV can create a partial impression of depth but viewing in its present form is never particularly good. Receiver are either more expensive with lower cost eye ware or

6 cheaper sets with expensive eye ware. The depth impression also is only apparent with objects fairly close to the camera. An alternative way to improve the viewing experience is to increaser the screen definition. The recently introduced 4K system doubles the horizontal and vertical resolution This will become 4096 by It will also provide a wider range of colours and improved dynamic range. The combination of thesae factors produces a much more realistic picture. The problem is that this requires a wider bandwidth and the current system has noe to spare. This means that unless a much better compression algorithm can be devised it will probably not be practical to implement 4K on broadcast channels so the quality may onlt be used on internet channels or on enhanced disk recordings. Netflix launched a 4K service in April 2014 for integrated TV s and Youtube has a 4K test area for pro-sumer generated content and Amazon Prime were launching a service in October. The next stage is projected to be 8K video which again will double the horizontal and vertical resolutions and it is very difficult to see how this could be implemented except by internet or recorded connections. David had intended to cover connected systems but time ran out so it may well be a topic for a future meeting David finished by giving his views on the future shape of TV Linear broadcasting will continue to be the main source of viewing. Time shifting will continue to increase, TV displays will get bigger. 4K is currently available on sets of 40 inches and larger. TV displays will get smaller with more people using tablets, PC s and phones. Pressure on bandwidth will increase and even more efficient coding techniques will be developed. The TV will be the hub for home automation, security and communication as well as entertainment. OPEN LETTER TO PC GROUP MEMBERS It is with considerable regret that I am having to leave the RMG PC Group especially as I had just taken over the role of Chairman and was looking forward to making a more significant contribution to steering the Group. However, our move to East Dorset will make attending meetings very much an occasional event for me rather than the regular attendee and contributor that I have enjoyed being over the last few years. I am intending to continue with Leslie s Puzzle Page and will be able to keep in touch via the Website and the Newsletter. 6

7 I have thoroughly enjoyed being a member of the Group and would like to thank you all for accepting me in your midst, for your camaraderie and for the stimulation of technical and other discussions that we have had. I have certainly learnt a lot from you and I hope that in a small way I have helped you in understanding some of the physics and mathematics behind modern day computing. Both Carole and I have enjoyed participating in the walks which many of you have led over the years and thanks go to Don for his enthusiasm and organisation of those walks. On moving we will be losing our addresses with domain name ntlworld and our landline telephone number. For the short term, until I can get organised with an ISP, we will be using a pebble which is a cobblestone sized device which provides Wi-Fi for up to 10 devices from the 3G and 4G mobile network using an EE SIM card. Today we have constructed a veritable mountain of boxes in the lounge which we will have to live with for a week. Clearing out and packing up is a bit like digging a hole in the garden; the hole is quite small but the pile of earth taken therefrom is huge. Best Regards Chris Rosenberg Outgoing Chairman 20th November MEETINGS ARE ON THE THIRD WEDNESDAY OF EACH MONTH THE MEETINGS WILL BE IN THE VILLAGE HALL AT NEWDIGATE (grid ref TQ ) A map and directions are available on the club website. The hall is available from 9.00 a.m until 1.00 p.m. The meeting commences at a.m for a.m. and will normally be the third Wednesday of the month. The next meeting is on Wednesday December 17th For the latest information on the program please see CURRENT AND PAST NEWSLETTERS CAN NOW BE DOWNLOADED FROM We are always looking for contributions to either the program or the Newsletter so if any member would like to give a talk or know anyone else capable please talk to the committee. A short note on your experiences might also make a useful addition to the newsletter and could provide a solution to someone else s problem. Please do not be shy and remember that what may seem obvious to you may help someone else to solve a difficult problem

8 LESLIE S PUZZLE PAGE contributed by Chris Rosenberg Clock hands The minute hand of a clock is twice as long as the hour hand. At what time after midnight does the tip of the minute hand move away from the tip of the hour hand at the fastest rate? Solution It is of course possible to solve this problem by deriving the magnitude of the vector connecting the two tips, differentiating w.r.t. time, equating to zero and solving for theta (the time dependent angle between the hands). However, if the problem is viewed from a frame of reference in which the minute hand is stationary then the hour hand rotates anticlockwise. The tip of that hand will be moving away from the tip of the minute hand at the greatest rate when the back projection of its velocity vector passes through the tip of the minute hand. In this situation the two hands and the velocity vector form a right angled triangle 2 1 ɵ Thus the angle theta = cos -1 (1/2) which is π/3. It is now only necessary to determine how much time has elapsed since midnight for the hands to have the relationship as shown. The angle between the hands after midnight is 12φ φ where φ is the angle moved through by the hour hand from 12. Thus 12φ φ = ɵ = π/3 Hence φ = π/33 and the elapsed time is (12/2π)(π/33) which is hours or 10.9 minutes. This month s puzzle: The charged projectile oooooooooooooooooo A particle of mass m and electric charge q is subject to the combined effects of gravity and a uniform horizontal electric field of strength E. It is projected with speed v in the vertical plane parallel with the field and at an angle ɵ to the horizontal. What is the maximum distance the particle can travel horizontally before its level has fallen to that of its starting point?