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FM Broadcast Range

  1. Aug 1, 2017 #1
    Hello, I am from Lahore, Pakistan,
    I have obtained a FM transmission License in Lahore.
    and i am about to set my radio station here in few days. i have ordered the equipment which will reach here in 5-7 days more.....
    here i am going to give you my broadcasting equipment details:
    now i am curious to know about the range or the area of coverage with this equipment (in Miles or Km's)

    Tranmitter:
    ArmStrong 2.5kW Solid State FM Amplifier
    Features:


    [Adjustable Power : 50 – 2500 Watts
    (I have to set it on 2.3kW)
    Frequency Range : 87.5/88 – 108 MHz
    Proven in the world’s worst environments by the US Military
    Automatic Power Factor Correction
    VSWR Foldback and Protection
    Automatic Power Output Control
    (Made in USA)]

    Antenna:
    ArmStrong FMA-707 8 – Bay Circularly Polarized FM Antennas

    Features:

    [True Circular Polarization
    Heavy Duty Brass Construction
    Type N Input, doesn’t not require pressurization
    Extremely Low Loss Power Divider
    Balance Feed Straps
    Factory Tuned to 95.0 MHz for Exceptional Performance
    (Made in USA)]

    200feet Tower will be used for antenna on a 58 feet roof top (Total height will be 258 feet) from ground level.

    now i am curious to know about the range or the area of coverage with this equipment (in Miles or Km's)

    Please give answer....... asap
     
    Last edited: Aug 1, 2017
  2. jcsd
  3. Aug 1, 2017 #2
    There are honestly a lot of factors which could affect the range such as the weather, the terrain around you, and how much radio noise is in the area. I would estimate that under good weather conditions, across flat terrain, and in a rural area, the range will extend to the horizon which is about 20 miles.
     
  4. Aug 1, 2017 #3

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    That antenna appears to be rated for 500W each. How are you planning on driving your 2500W into it/them?

    http://www.armstrongtx.com/pdf/fma-707.pdf
     
  5. Aug 1, 2017 #4
    Hello,
    This is 8 bay antenna
    Each bay carry 500W
     
  6. Aug 1, 2017 #5

    sophiecentaur

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    Science Advisor
    Gold Member

    Mostly, when people spend a load of money on a Broadcast radio transmitter, they have planned for a certain coverage and for protection of distant services from outgoing interference - i.e. you plan, then you buy. Doesn't your licensing authority have any idea about the effect of your presence on the existing network? Amazing; they just issued you with a licence for kiloWatts of transmissions.
    Doesn't the ITU have anything to say about that?
     
  7. Aug 1, 2017 #6

    davenn

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    Science Advisor
    Gold Member


    agreed

    there's a program called Radio Mobile designed specifically for mapping coverage area that may help you out
     
  8. Aug 2, 2017 #7
    I would expect the Licensing Authority to have worked out the coverage area, as mentioned by Sophie Centaur.
    The problem is that the range is likely to be dictated by interference from other stations, which makes it impossible to predict.
    A paper on the topic of required field strength for FM planning, based on UK conditions, is at the following URL:
    https://www.ofcom.org.uk/__data/assets/pdf_file/0013/54310/annex-f.pdf
    This suggests a minimum field strength for a portable receiver of 40 dBuV/m, whereas the primary service area would require 60 dBuV/m, giving Hi Fi reception.
    It is interesting how the situation has changed over the half century since FM started in the UK (USA is different). First of all it was expected that roof mounted Yagis would be used, although the receivers were rather poor. Ignition interference was the main problem. Then stereo was introduced, which created a severe performance penalty, and car and portable receivers for FM became more common. Receivers improved with the use of low noise transistors, and finally, local broadcasting started, creating an interference limited situation. So we are now roughly where we were in 1955!
    The ITU published the following document giving curves of field strength versus distance for various situations:-
    http://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.370-7-199510-W!!PDF-E.pdf
    Your transmitter ERP can be worked out as follows:-
    TX power 2.3kW = +33.6 dBW
    Antenna gain +4 dBd circular polarisation
    Antenna gain +1 dB for linear pol. RX antenna
    ERP = 33.6 + 1 = 34.6 dBW
    Therefore the ITU curves, which are based on 1kW ERP, should be adjusted by 4.6dB.
    Assuming an interference-free environment and using the ITU curves, I obtain a range of 40km for the primary service area, giving Hi Fi reception, and 80km for a portable receiver where quality is unimportant.
    Finally, the terrain in Lahore is unknown to me and may alter the coverage considerable where there are hills, valleys and high buildings.
     
  9. Aug 2, 2017 #8

    sophiecentaur

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    Science Advisor
    Gold Member

    That's only half of the equation, though. If the station is Independent, it will be funded by advertising and the income will be related to the audience size (and demographic). Running and capital costs are affected by service area size and it is easy to find that costly Watts are finding they way to areas with no population or adverse terrain. Advertising revenue is never over-lavish so is the station going to sustain itself?
    The whole project seems odd to me, as an Engineer. The BBC and other serious broadcasters wouldn't consider putting up a transmitter until they were sure that it was matched to the requirement. Perhaps that's why a number of would-be broadcasting companies fail - poor planning.
     
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