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Thread: using walkie talkie on SMRT trains

  1. #21

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by Canew View Post
    Bro Astin, I am no expert, but what I've read, there is a line of sight consideration even for radio frequency.

    Here is an explanation from Wikipedia: http://en.wikipedia.org/wiki/Line_of_sight
    "Radio signals, like all electromagnetic radiation, travel in straight lines."

    Another statement: http://en.wikipedia.org/wiki/Non-lin...ht_propagation
    "Many types of radio transmissions depend, to varying degrees, on line of sight between the transmitter and receiver. Obstacles that commonly cause Non Line Of Sight conditions include buildings, trees, hills, mountains, and, in some cases, high voltage electric power lines. Some of these obstructions reflect certain radio frequencies, while some simply absorb or garble the signals; but, in either case, they limit the use of many types of radio transmissions."
    Walkie-talkie, cell phones uses UHF signals, and are not restricted by line-of-sight. LF to HF radio signals needs LOS.

    BC

  2. #22
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by firefly99 View Post
    I have been using Motorola T4503 walkie talkie (3km range) when out shopping with my buddies. In general, they work well in most part of Singapore. Even on the SMRT train platform, as in from one end to the other end of the platform.
    Think about using a flashlight that can be seen from 3km away in a clear night in muddy water.

  3. #23
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by Scaglietti View Post
    Walkie-talkie, cell phones uses UHF signals, and are not restricted by line-of-sight. LF to HF radio signals needs LOS.

    BC
    It is exactly the other way round. Otherwise people wouldn't be able to enjoy international broadcasts on shortwave (HF) radio.

  4. #24
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by Astin View Post
    Maybe we can ask those security officers in shopping centres, they should know better...
    I'm sure those security officers dont use cheapo 3KM range walkie talkie. Those walkie talkies used by security, building management and police officer are of a different range.

  5. #25
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by ortega View Post
    you and your friend don't like each other?
    sit together lor
    Maybe got BO huh!

  6. #26
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by Scaglietti View Post
    Walkie-talkie, cell phones uses UHF signals, and are not restricted by line-of-sight. LF to HF radio signals needs LOS.

    BC
    not true.

  7. #27

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by zekai View Post
    not true.
    Yup, realised that I was wrong...

    BC

  8. #28

    Default Re: using walkie talkie on SMRT trains

    A metal cage of the train acts like a Faraday's cage, which is probably why the signal loss might be significant.

  9. #29
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by waipeng View Post
    A metal cage of the train acts like a Faraday's cage, which is probably why the signal loss might be significant.
    Nope. A conducting hull would actually act as a waveguide and reduce signal loss.

    What happens in a crowded trains are mainly two things: 1) receiver performance is likely affected by electrical interference, and 2) the vast majority of transmitted radio energy is not spent on communicating, but microwaving your fellow passengers.

  10. #30
    vince123123
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    Default Re: using walkie talkie on SMRT trains

    There is a big difference between line of SIGHT, and the waves travelling in straight lines. Line of sight imples no impediment at all (save for air), ie you can SEE one end to the other.


  11. #31

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by jtb View Post
    This set of talkies has a low transmission range at lower power and agreed it will never work. Try another high power version maybe more than 1Watts, you will receive the transmission. Nothing to do with interference but the quality of the set itself.
    Agreed the T4503 is a low end set rated at 3Km and 0.5W. The length of a SMRT train is less than 1KM more likely 500m.
    I had tried other high power pair of talkies such as GP328, GP2000 transmitting at 4W with same results in train carriage.

    Suspect it is due to electrical interference. Need someone to verify and confirm.

    Quote Originally Posted by Astin
    Maybe we can ask those security officers in shopping centres, they should know better....
    Don't bother to ask those security officers, they do not know.
    Last edited by firefly99; 27th September 2007 at 10:18 AM. Reason: additions

  12. #32

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by firefly99 View Post
    I have been using Motorola T4503 walkie talkie (3km range) when out shopping with my buddies. In general, they work well in most part of Singapore. Even on the SMRT train platform, as in from one end to the other end of the platform.

    However, when we board the same train, first and last carriage, the walkie talkie set would not be able to establish the radio link. Do not think it is an issue with the range, since the moment both of us step out of the train carriage, radio link is reestablished.

    We had tried using other more powerful walkie talkie sets with the same results.

    Anyone had this experience or know what is the cause ?

    Please advise. Thanks.
    The train is like a lossy waveguide and thus, the wave would not propagate down the direction of the train. Very much the same why you cannot receive radio in MRT tunnels.
    Last edited by lsisaxon; 27th September 2007 at 10:28 AM.

  13. #33

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by firefly99 View Post
    Agreed the T4503 is a low end set rated at 3Km and 0.5W. The length of a SMRT train is less than 1KM more likely 500m.
    I had tried other high power pair of talkies such as GP328, GP2000 transmitting at 4W with same results in train carriage.

    Suspect it is due to electrical interference. Need someone to verify and confirm.

    Don't bother to ask those security officers, they do not know.
    Anything with higher power will require IDA approval.

  14. #34

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by lsisaxon View Post
    The train is like a lossy waveguide and thus, the wave would not propagate down the direction of the train. Very much the same why you cannot receive radio in MRT tunnels.
    Sorry, could you explain what is a "lossy waveguide". Thanks.

    Understand talkies more than 4 or 5W requires IDA approval.

  15. #35
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    Default Re: using walkie talkie on SMRT trains

    You should try it in a train that is not crowded with people.

  16. #36
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    Default Re: using walkie talkie on SMRT trains

    Electronics interference by strong magnetic waves within the train system (and carriage) may have resulted in the loss or weak transmission signals.

    One major source of Electromagnetic waves that is quite stong in the train is from the DC motors that the trains runs on.

    While in my undergrad days....as i was studying some EMC and motor realated stuff, we used to carry those small "wristwatch compass" and observe the magnetic flux change during train acceleration, braking etc...

    All these may adds up to the actual radio signal of the walkies i guess.

    The walkies signal may be attenuated due to the large amount of metallic caging of the train coaches.
    Last edited by sulhan; 27th September 2007 at 12:26 PM.

  17. #37
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by firefly99 View Post
    Sorry, could you explain what is a "lossy waveguide". Thanks.
    A waveguide is any structure that guides waves, i.e. limits their uncontrolled spread, or directs them into specific directions.

    A cable is a waveguide. A glass fibre is a waveguide. A hollow tube (such as an MRT car) can be a waveguide. A sewage drain is a waveguide (for water waves). The earth's surface and the ionosphere form a waveguide. Etc.

    A "lossy" waveguide is a waveguide that causes signal/power loss, i.e. it absorbs part of the energy while guiding the wave, and the wave gets attenuated as it travels along.

    Understand talkies more than 4 or 5W requires IDA approval.
    ALL radio communication equipment in Singapore requires IDA approval. Many of the walkie talkies sold in Singapore are illegal. The power limit for walkie talkies approved for general use is almost certainly much less than what you think, probably around 500mW. Some radios on sale also use frequencies that are illegal in Singapore (note that there are several different standards for "personal radio" style walkie-talkies - i.e. the US uses 465/467 MHz, while Europe uses the 446 MHz region; there are also some low power devices in the 433 MHz band.)

    Technically, mere possession of an unlicensed radio could land you in jail. Singapore is paranoid and extremely restrictive about any kind of uncensored/uncontrolled communication (to the point where even some licensed users of handy-talkies have to declare one week in advance when and where they are going to use them). But as always, laws are only enforced when it is convenient to the authorities.
    Last edited by LittleWolf; 27th September 2007 at 12:49 PM.

  18. #38

    Default Re: using walkie talkie on SMRT trains

    Maybe because... MRT pple want to disable ladio control device or B.O.M.B in the train..
    so they have install jamming devices on the train itself..

    my 2 cents worth of conspiracy theroy
    40D 50mmF1.8 17-85mm 24-70L

  19. #39
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by lsisaxon View Post
    Anything with higher power will require IDA approval.
    Higher power in this case is a classic "brute force" (as opposed to intelligent) solution. 4 watts of RF power is frequently sufficient for intercontinental voice radio communications; if the same power doesn't suffice for the length of an MRT car, this is an indication that something else is wrong.

  20. #40

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by firefly99 View Post
    Sorry, could you explain what is a "lossy waveguide". Thanks.

    Understand talkies more than 4 or 5W requires IDA approval.
    Someone already explained "lossy waveguide".

    Depends on the band. For example, GSM phones are able to pump out 2W but they have to be approved for sale.

    For walkie-talkies using the 446MHz bands (it's not compatible with US FRS band), IDA licensed the 446.0MHz to 446.1MHz for shared public use and with a max power of 500mW.
    http://www.ida.gov.sg/doc/Policies%20and%20Regulation/Policies_and_Regulation_Level2/IDA_TS_LMR_i1r1_(Aug_06).pdf

    Other walkie talkies have to have a site license, otherwise you'll have to have a HAM (Amateur Radio) Licence to own one. The reason is because you have to be responsible enough not to cause interference to other devices operating in the frequency range.
    Last edited by lsisaxon; 27th September 2007 at 06:36 PM.

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