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Why is radio spectrum allocation based on archaic models?

  1. Dec 22, 2015 #1
    The FCC's propagation models for the FM broadcast band seem grotesquely inaccurate in some places, where stations can be received that the models say are absolutely out of range. I'm not even talking about DX conditions like ducting or skip, I'm talking about baseline. When I lived in Fayetteville, AR for instance, I could often listen to 99.5 FM from Tulsa, OK over the local station on the same frequency, even though the FCC data said this should be impossible by 3-4 orders of magnitude in signal strength!

    Clarly there is a lack of field observations to test the limits of these models/approximations. They are presumably only tested under a narrow range of conditions, not on non-ideal, "real world" scenarios with buildings, hills, city, suburbs, persistent atmospheric temperature inversions, etc.

    Why has there not been a bigger push for better observations?
     
  2. jcsd
  3. Dec 22, 2015 #2

    davenn

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    and what has this to do with you thread title ?

    nothing that I can see


    lots of things may have changed in a particular area between when they did their tests and when you did your listening VHF propagation is easily affected by buildings, tree/bushland growth etc etc
    maybe there's even been changes in transmitter power levels that you are unaware of ???

    Also, published figures are likely to err on the cautious/conservative side ... last thing FCC would want if
    for lots of people complaining that they cant hear stations that the FCC said they would.

    I seriously doubt that is true unless you can supply specific and reliable info to the contrary


    Dave
     
    Last edited: Dec 22, 2015
  4. Dec 22, 2015 #3

    dlgoff

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    Funny you bring this up as just a month or so ago I received a digital TV channel signal from Fayetteville up here in Kansas. Next day ... gone.
     
  5. Dec 22, 2015 #4

    davenn

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    nice bit of long haul VHF/UHF DX :)
     
  6. Dec 22, 2015 #5
    Local atmospheric conditions can do that sort of thing, shortwave radio is reflected back to the surface by the ionosphere.
    The ionosphere is not like a perfect mirror though and it's changeable, so unpredictable receptions from distant stations are not uncommon.
     
  7. Dec 22, 2015 #6
    The frequency allocation was determined by law years ago. However, commercial FM station & TV frequencies are essentially line-of-sight allocations. Local weather conditions will cause overlaps at the edges of the signal. As a HAM operator, when atmospheric are right, I have been able to communicate with other operators in Argentina and Europe as easy as talking on a phone using SW frequencies.
     
  8. Dec 22, 2015 #7

    meBigGuy

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    I'm not saying that the models, goals, or methodologies used to determine RF allocations are not archaic or chaotic or impractical, but your example is not a significant example to prove that point without supporting terrain data, antenna directionality (yours and the other stations) and so on.
    Also, there is a fair amount of politics, etc that can affect any single decision.

    If you are just talking frequency spacing/location/power of stations in the FM band, then their methodology seems to work well for the most part.
     
  9. Dec 23, 2015 #8

    tech99

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    Frequency allocations are subject to Recommendations made by the International Telecommunications Union, of which the FCC is a member. The ITU has researched propagation for more than half a century, and publishes curves for broadcast planning. The curves gives the statistical probability of various signal strengths being exceeded at great distances, and this is used in conjunction with the recommended protection ratio (i.e. the required signal to interference ratio) for FM broadcasting. Of course, anything can happen for a small percentage of the time.
     
  10. Dec 23, 2015 #9

    sophiecentaur

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    Yes, it's the politics that are the main factor involved with spectrum planning and service planning.
    Service planning within a country can be arranged to make very efficient use of spectrum space at VHF and UHF when the planning authority actually has some authority. The UK UHF TV network was so well planned that there was room for a fifth channel in the available UHF TV bands. That hasn't been the case where regulation has not been so enforceable and the broadcasting has been mostly commercial and localised.
    But the same problems exist for satellite broadcasting and the CCIR has just the same difficulty in allocating channels, powers and footprint sizes and shapes in the broadcast channels as they did with terrestrial systems.
    Basically, the telephone companies don't care about minority mobile phone services because there's not enough money in it. That's what happens with free enterprise and / or small government. But one could argue that minorities are not of any consequence.
     
  11. Dec 23, 2015 #10

    jim hardy

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  12. Dec 24, 2015 #11

    sophiecentaur

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    Both very omindirectional. When there's a worry about co channel interference, it is possible to use a transmitter, sited on one side of the service area, firing away from a vulnerable nearby area and the minor transmitter there may well be sited firing towards the main interferer so receiving antennae will be looking away from the interference. Not such a useful strategy now that most people use whip antennas, on each receiver.
    Directional antennae are much more expensive and broadcasters may not be too interested in providing protection unless there is a tight regulatory regime. Local commercial radio would usually not give a damn. and a cheap 'omni' is the solution that makes sense to them.
     
  13. Dec 24, 2015 #12

    jim hardy

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    Hopefully OP will get interested.
    I live 80 miles from 30 kw FM station that played 1940's country(Hank Snow, Red Foley, Little Jimmy Dickens etc), we are just outside its fringe per map .
    Adding two elements to a ordinary FM folded dipole, turning it into a Yagi made reception pretty reliable - all my friends "Just had to have one"
     
  14. Dec 26, 2015 #13

    sophiecentaur

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    Re-reading the title of the thread and the OP's wording, it reads like a rant with very little basis. The only "archaic" thing about the planning is that the plans were made many decades ago and things (like spectrum use and new modulation systems) change. But the planning arrangements were made from a very well informed perspective - including detailed measurements and were pretty well optimal at the time. (In the UK, at least). New systems have to be Compatible with existing services. (haha)
    In the UK, the aim has been to serve the vast majority of the population (the high 90s of percent, afair) at a reasonable cost. The plan had a particular receiving installation in mind but people now want whip antennas (or even just earphone leads) on their portable audio receivers so the goal posts have been moved.
    We can say, for certain, that things are a lot better than they every would have been with a free- for all arrangement, which is what broadcasting started off with. Many countries still hang on to frequency allocations that they grabbed (just like the land, grabbed by their grandfathers). The ITU has done a pretty good job, considering and any failure has nothing to do with the 'sums'.

    I would reckon that the comms services (Phone and data) we want in the UK are pretty inadequate, compared with the available broadcast services (analogue and digital). That just has to be because they are laid on by commercial organisations which are out to maximise their profit at the expense of the marginal few customers. There is no 'penny post' philosophy there.
     
  15. Dec 26, 2015 #14

    jim hardy

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    well , yes it does.
    I'm guilty of that - anything that doesn't fit my preconceived notions of how it should work gets a rant - eg Windows.
    But i'm old enough to play the "Grumpy Old Man" card .
     
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