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FM and DAB Broadcast infrastructure

[Deleted User][Deleted User] Posts: 4
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in Technical #1
Hi there, I am a 4th year computer networking student currently writing a report on the modulation techniques used in FM and DAB radio in the UK.

I want to start the report with discussing the UK boradcast infrastructure, but this is an area somewhat different to my expertise. My report is going to focus on national radio such as Radio 1 and 2 for the examples.

I have searched around the internet for information on the FM and DAB Broadcast infrastructure, but I am struggling to find any good information (especially for FM radio).

What am looking for is the locations of the transmitters, the types of antennae used and any other technical information you may think is relevant.

As I say this is outwith my expertise. I know there are many amature and professional experts on this forum, I would be extremaly greatful for if you could share your expertise and provide me with some advice or links with relevant and useful information.

Thanks in advance. :)

Comments

  • fmradiotuner1fmradiotuner1 Posts: 20,496
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    #2
    Have a look at
    http://tx.mb21.co.uk/
    And
    http://www.thebigtower.com/live/INDEX/Index.htm
    Quite a few pictures and info here on these sites.
  • [Deleted User][Deleted User] Posts: 4
    Forum Member
    #3
    Thanks for links fmradiotuner1, some useful information in them. One thing they appear to missing in information on the types of antennae used. Really the key information I am looking for is if they are omnidirectional, directional or a mix of them both? I assume they are omnidirectional, but as I am righting a report, I want to be sure of my facts before I hand it in.
  • Nigel GoodwinNigel Goodwin Posts: 58,465
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    #4
    F1Senna wrote: »
    Thanks for links fmradiotuner1, some useful information in them. One thing they appear to missing in information on the types of antennae used. Really the key information I am looking for is if they are omnidirectional, directional or a mix of them both? I assume they are omnidirectional, but as I am righting a report, I want to be sure of my facts before I hand it in.

    Certainly many TV transmitters aren't omnidirectional, so FM and DAB might not be as well?
  • chrisjrchrisjr Posts: 33,282
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    #5
    F1Senna wrote: »
    Thanks for links fmradiotuner1, some useful information in them. One thing they appear to missing in information on the types of antennae used. Really the key information I am looking for is if they are omnidirectional, directional or a mix of them both? I assume they are omnidirectional, but as I am righting a report, I want to be sure of my facts before I hand it in.

    Some sites will be entirely omni, some will be entirely directional and some sites may have a mix of both. And you may not know simply by looking at the antenna system either.

    A transmitter may have several individual antennas pointing in different directions forming a complex array system. If they are all fed equal power then the radiation pattern will be pretty much omni directional.

    However certain antennas may be fed at a lower power than others so restricting the transmission range in certain directions. This is often used to protect other transmitters on similar frequencies from interference or to tailor the radiation pattern to the licensed service area of the radio station being broadcast.

    The only way to tell would be to look at the Ofcom transmission area maps. There are some available to the public but they don't give the same level of detail as those the broadcasters get to see. And a lot of them are somewhat out of date, see

    http://www.ofcom.org.uk/static/radiolicensing/mcamaps/MCAs.htm
  • [Deleted User][Deleted User] Posts: 4
    Forum Member
    #6
    Nigel Goodwin wrote: »
    Certainly many TV transmitters aren't omnidirectional, so FM and DAB might not be as well?

    I thought this may be the case Nigel, trying to find out detailed information is proving difficult. My report is only 2000 words, the part about transmitters is only about 200 words to provide a bit of context.
  • [Deleted User][Deleted User] Posts: 4
    Forum Member
    #7
    chrisjr wrote: »
    Some sites will be entirely omni, some will be entirely directional and some sites may have a mix of both. And you may not know simply by looking at the antenna system either.

    A transmitter may have several individual antennas pointing in different directions forming a complex array system. If they are all fed equal power then the radiation pattern will be pretty much omni directional.

    However certain antennas may be fed at a lower power than others so restricting the transmission range in certain directions. This is often used to protect other transmitters on similar frequencies from interference or to tailor the radiation pattern to the licensed service area of the radio station being broadcast.

    The only way to tell would be to look at the Ofcom transmission area maps. There are some available to the public but they don't give the same level of detail as those the broadcasters get to see. And a lot of them are somewhat out of date, see

    http://www.ofcom.org.uk/static/radiolicensing/mcamaps/MCAs.htm

    Thanks for this I will have a look.
  • spiney2spiney2 Posts: 27,058
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    #8
    http://stakeholders.ofcom.org.uk/binaries/consultations/dab-coverage-planning/annexes/annex-g.pdf

    http://stakeholders.ofcom.org.uk/binaries/consultations/dab-coverage-planning/annexes/annex-f.pdf

    http://www.mds975.co.uk/txmaps/txmaps.html
  • JamesEJamesE Posts: 6,456
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    #9
    Before you submit your report, you must check your spelling and grammar:

    extremaly – extremely: amature – amateur: different to – different from.
  • Mark CMark C Posts: 20,894
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    #10
    chrisjr wrote: »
    Some sites will be entirely omni, some will be entirely directional and some sites may have a mix of both. And you may not know simply by looking at the antenna system either.

    A transmitter may have several individual antennas pointing in different directions forming a complex array system. If they are all fed equal power then the radiation pattern will be pretty much omni directional.

    However certain antennas may be fed at a lower power than others so restricting the transmission range in certain directions. This is often used to protect other transmitters on similar frequencies from interference or to tailor the radiation pattern to the licensed service area of the radio station being broadcast.

    The only way to tell would be to look at the Ofcom transmission area maps. There are some available to the public but they don't give the same level of detail as those the broadcasters get to see. And a lot of them are somewhat out of date, see

    http://www.ofcom.org.uk/static/radiolicensing/mcamaps/MCAs.htm

    Take a look at the FM/DAB/AM spreetsheet here

    http://stakeholders.ofcom.org.uk/broadcasting/guidance/tech-guidance/tech_parameters/

    It gives directional characteristics for all UK FM and DAB transmitters in H and V planes, in 10 degree increments. Stations that are omni directional have no data in those fields. The figures are attenuation relative to unity. i.e 0 is full power, 15 would be the rated ERP 15dB down.
  • spiney2spiney2 Posts: 27,058
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    #11
    the thing about cofdm is, its great for 2 way links, where you can "closely approach the shannon data rate limit". wi fi for example. but not anything like as good in broadcasting, where the transmitter cannot "optimise the send channel". so the powerr rolloff in urban areas is effectively an inverse fourth power law (just like mobile phones) and many more transmmitters are needed than first thought, for dab and dtt. basically, because the planners were complete gits and used a stupidly simple model to predict likely coverage ......
  • spiney2spiney2 Posts: 27,058
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    #12
    ..... the other problem specifically with dab ...... typically - everything else being equal which it isnt - then you need around one fifth the transmitter power for same area coverage (before viterbi decoding is defeated by receiver input noise). but,the power needed in a typical dab receiver is MUCH greater ! since there are now several consecutive stages of signal processing requiring large dsp chips instead of just a diode or simple analogue ic ........ hence the battery consumption issue .....
  • kjhskj75kjhskj75 Posts: 2,995
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    #13
    A couple of years ago I made this:

    http://www.kjhskj75z.talktalk.net/radio/

    which may be of some help to you.
  • barbelerbarbeler Posts: 23,827
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    #14
    JamesE wrote: »
    Before you submit your report, you must check your spelling and grammar:

    extremaly – extremely: amature – amateur: different to – different from.
    "with discussing" - by discussing; "is the locations of the transmitters" - are the locations of the transmitters; "greatful" - grateful. Is "outwith" a Scottish thing?

    Just trying to be helpful :D
  • MartinPickeringMartinPickering Posts: 3,711
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    #15
    F1Senna wrote: »
    but as I am righting a report, I want to be sure of my facts before I hand it in.

    I'm going to agree with the grammar patrol and suggest you get help in copy-editing your report.

    I'm not clear on whether you are asking about receiving aerials or transmitting aerials.

    Coverage maps:-
    http://www.mds975.co.uk/txmaps/txmaps.html
  • TonyCurrieTonyCurrie Posts: 835
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    #16
    barbeler wrote: »
    "with discussing" - by discussing; "is the locations of the transmitters" - are the locations of the transmitters; "greatful" - grateful. Is "outwith" a Scottish thing?

    Just trying to be helpful :D

    "Outwith" is a widely used word meaning 'beyond' or 'outside'. Its use outwith Scotland is limited to parts of Northern England.
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