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Thread: using walkie talkie on SMRT trains

  1. #41

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by LittleWolf View Post
    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.
    hi LittleWolf, Yes the question is "if the 4W doesn't suffice for the length of an MRT car" what else could be the cause ?

    Quote Originally Posted by lsisaxon View Post
    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.
    hi lsisaxon, Yes I am aware of the differences between PMR446/FRS/GMRS and a max power of 500mW for Singapore approved, license free models.

    A question slightly OT: If a GP328 is programmed with PMR446/FRS/GMRS frequencies. This would enable me to use the correct license free frequencies at different countries and prevent any interferences. As in locally, I use the GP328 with 446 frequencies at 500mW and overseas as in US, I use FRS/GMRS frequencies at 2W or 4W. Would I run foul of any law ? Please advise. Thanks.
    Last edited by firefly99; 28th September 2007 at 02:10 PM. Reason: additions

  2. #42

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by Majest1c View Post
    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
    hmm can't they trigger it with handphones too? hp works just fine on trains..

  3. #43
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by firefly99 View Post
    hi LittleWolf, Yes the question is "if the 4W doesn't suffice for the length of an MRT car" what else could be the cause ?
    Interference & absorption? To get the definite, non-speculative answer, one would have to resort to measurements. But you'll probably get in trouble if you unpack any sophisticated measurement equipment in a train ...

    If a GP328 is programmed with PMR446/FRS/GMRS frequencies. This would enable me to use the correct license free frequencies at different countries and prevent any interferences. As in locally, I use the GP328 with 446 frequencies at 500mW and overseas as in US, I use FRS/GMRS frequencies at 2W or 4W. Would I run foul of any law ?
    It's illegal in most (possibly all) countries. Equipment needs to be type approved for the specific radio service, and the standard requirement for approval is that the equipment can not be used on unauthorized frequencies. (There are some very limited exceptions in the European Union, though.) Singapore is extremely restrictive in every respect; usually, the only service that is allowed to use non-type approved equipment is the amateur radio service (but Singapore apparently doesn't even allow this). I.e., a licensed ham (in the US) can modify a FRS radio for use on the amateur bands, but it is illegal to use a ham transceiver modified to work on the FRS bands, even if the technical specifications were fulfilled.

    Also note that GMRS in the US is not "free for all", but requires a license (paperwork and $$$).

  4. #44

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by LittleWolf View Post
    Interference & absorption? To get the definite, non-speculative answer, one would have to resort to measurements. But you'll probably get in trouble if you unpack any sophisticated measurement equipment in a train ...

    It's illegal in most (possibly all) countries. Equipment needs to be type approved for the specific radio service, and the standard requirement for approval is that the equipment can not be used on unauthorized frequencies. (There are some very limited exceptions in the European Union, though.) Singapore is extremely restrictive in every respect; usually, the only service that is allowed to use non-type approved equipment is the amateur radio service (but Singapore apparently doesn't even allow this). I.e., a licensed ham (in the US) can modify a FRS radio for use on the amateur bands, but it is illegal to use a ham transceiver modified to work on the FRS bands, even if the technical specifications were fulfilled.

    Also note that GMRS in the US is not "free for all", but requires a license (paperwork and $$$).
    LittleWolf, Thank you very much for your advice.

  5. #45
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    Default Re: using walkie talkie on SMRT trains

    Might doppler affect also be causing attenuation of the signal?

    I read in a bike forum that they tried to use walkies for bike to bike comms when on the move and they had problems, even when there is not much traffic and they are not too far apart, possibly cause of this doppler effect, where the rf signal is transmitted and received from a moving object.

  6. #46
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by blueayz View Post
    Might doppler affect also be causing attenuation of the signal?

    I read in a bike forum that they tried to use walkies for bike to bike comms when on the move and they had problems, even when there is not much traffic and they are not too far apart, possibly cause of this doppler effect, where the rf signal is transmitted and received from a moving object.
    The Doppler effect is of concern when communicating with satellites that move at kilometres per second speeds. Bikes don't move fast enough to give significant frequency shifts. Also, in an MRT, both parties don't move relative to each other (they go at the same speed in the same direction), so this is a non-issue.

    One thing that affects the performance of cheap consumer radios is of course that the receivers are usually crap - they may go pretty deaf in the presence of signals on other frequencies. Plus, a lot of cheap electrical appliances sold here are effective radio jammers (IDA is probably too busy preventing responsible people from using radios than taking enforcement action against trashy electronics importers/manufacturers).

    Also, if the radios use squelch (and preset squelch levels are generally fairly high to mask the receiver flaws), the radios will not unmute even if there still is a usable signal. Some radios may have a "monitor" or "unsquelch" button, one could try that to see whether there's a signal.

    I'm not sure if tone-coded squelch (often advertised as "privacy codes") is legal in Singapore, but a lot of such radios are advertised as having more "channels", which is an outright lie (like so much what you read in marketing & advertising). Tone-coded squelch helps to separate different parties using the same frequency, but only one party can use the frequency at any one time. If two or more parties transmit on the same channel (in the erronous belief that the channel is free, because they didn't hear anything though their tone squelch), they unknowingly jam each other. This problem can also be recognized if the radio has a "monitor" button, which lets you hear whether there are other parties before transmitting.

  7. #47

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by blueayz View Post
    Might doppler affect also be causing attenuation of the signal?

    I read in a bike forum that they tried to use walkies for bike to bike comms when on the move and they had problems, even when there is not much traffic and they are not too far apart, possibly cause of this doppler effect, where the rf signal is transmitted and received from a moving object.
    The velocity in the front of the train and the back of the train should be the same if the train is travelling in a straight line..

  8. #48

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by LittleWolf View Post
    The Doppler effect is of concern when communicating with satellites that move at kilometres per second speeds. Bikes don't move fast enough to give significant frequency shifts. Also, in an MRT, both parties don't move relative to each other (they go at the same speed in the same direction), so this is a non-issue.

    One thing that affects the performance of cheap consumer radios is of course that the receivers are usually crap - they may go pretty deaf in the presence of signals on other frequencies. Plus, a lot of cheap electrical appliances sold here are effective radio jammers (IDA is probably too busy preventing responsible people from using radios than taking enforcement action against trashy electronics importers/manufacturers).

    Also, if the radios use squelch (and preset squelch levels are generally fairly high to mask the receiver flaws), the radios will not unmute even if there still is a usable signal. Some radios may have a "monitor" or "unsquelch" button, one could try that to see whether there's a signal.

    I'm not sure if tone-coded squelch (often advertised as "privacy codes") is legal in Singapore, but a lot of such radios are advertised as having more "channels", which is an outright lie (like so much what you read in marketing & advertising). Tone-coded squelch helps to separate different parties using the same frequency, but only one party can use the frequency at any one time. If two or more parties transmit on the same channel (in the erronous belief that the channel is free, because they didn't hear anything though their tone squelch), they unknowingly jam each other. This problem can also be recognized if the radio has a "monitor" button, which lets you hear whether there are other parties before transmitting.
    It's more likely to be multipath fading. There is still Doppler effect otherwise the speed radar would not work.

    Tone squelch (CTCSS) is legal because it is still within the voice channel, so it has nothing to do with the RF signal. That is also why the power of such devices has to be low and used for short range only because you don't want to jam another network.
    Last edited by lsisaxon; 29th September 2007 at 11:12 PM.

  9. #49
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by lsisaxon View Post
    It's more likely to be multipath fading. There is still Doppler effect otherwise the speed radar would not work.
    Speed radar uses higher frequencies, so the Doppler shift is also increased. Also, while the Doppler effect is certainly measurable, the frequency can be off by a kHz or more for a FM radio without affecting communication. In fact, the frequency may be off on the order of a few hundred Hz anyway as it is not so easy to get better frequency stability/accuracy.

    Tone squelch (CTCSS) is legal because it is still within the voice channel, so it has nothing to do with the RF signal.
    It's quite possible that it's legal, but not for this reason. Regulations are usually not based on what makes sense from an engineering/technology standpoint, but what authorities do not want people to do. E.g., you're not allowed to build repeaters for personal radio services, although this wouldn't do anything that is otherwise not in compliance with the technical specifications.

  10. #50

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by LittleWolf View Post
    Speed radar uses higher frequencies, so the Doppler shift is also increased. Also, while the Doppler effect is certainly measurable, the frequency can be off by a kHz or more for a FM radio without affecting communication. In fact, the frequency may be off on the order of a few hundred Hz anyway as it is not so easy to get better frequency stability/accuracy.

    It's quite possible that it's legal, but not for this reason. Regulations are usually not based on what makes sense from an engineering/technology standpoint, but what authorities do not want people to do. E.g., you're not allowed to build repeaters for personal radio services, although this wouldn't do anything that is otherwise not in compliance with the technical specifications.
    Well yeah.. Doppler effect is still there but it's certainly negligble for communications purposes.

    Well. If you want to build a repeater, then it's probably got to use 2 channels. Anyway, not easy to build a repeater because you'll need to use a notch trap on the receiver to prevent the transmitter from overloading your receiver.

    Alternatively, get a ham licence.

  11. #51
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    Default Re: using walkie talkie on SMRT trains

    dunno about mrt or doppler effect. *peng*
    my 8km motorola sets can typically receive only up to 400m. lol.
    Canon EF prime, macro & L lenses on EOS30D

  12. #52
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by lsisaxon View Post
    Alternatively, get a ham licence.
    I have one, but not in Singapore. Still wondering if it's worth the hassle, given all the ludicrous restrictions.

  13. #53

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by LittleWolf View Post
    I have one, but not in Singapore. Still wondering if it's worth the hassle, given all the ludicrous restrictions.
    No, it's not quite worth it.. Although, I'm no longer operating, I'm still paying $50 a year to keep my callsign. Now with internet chat and moobile phones, it doesn't really make sense to try to establish a SW call unless you're into DXing and collecting QSL cards. Plus I don't think HDB will allow setting up of a long wire antenna on the roof.

    There is no longer the need for Morse Code exam anymore. Just take the theory exam and you get a full license. I got my restricted license automatically upgraded to full license but I don't have SW equipment, only a Kenwood 5W VHF handset, a Diamond antenna and not many people to talk to.
    Last edited by lsisaxon; 2nd October 2007 at 10:34 AM.

  14. #54

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by Antzzz View Post
    dunno about mrt or doppler effect. *peng*
    my 8km motorola sets can typically receive only up to 400m. lol.
    You'll probably need a wide open space with no interference to push the range to 8km.

  15. #55
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    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by lsisaxon View Post
    Now with internet chat and moobile phones, it doesn't really make sense to try to establish a SW call unless you're into DXing and collecting QSL cards.
    QRPing. Preferrably QRP portable. I had lots of fun in the US talking to Europe with a few watts and a wire up the tree. That isn't much fun though if you have to tell IDA a week in advance when & where you're going to play radio - I want to operate spontaneously when conditions are good. And foxhunting - no fun if you have to declare your hideout ...

    Morse code isn't a problem (ok, I'll have to brush up, but 5wpm still can). More the requirements on antenna setups which pretty much mean you must have landed property to do anything using a fixed station. And the strict regulations that effectively prevent homebrewing and experimenting (apparently there's no exemption for homebuilt/modified equipment from type acceptance, which means $$$$ for getting them certified/tested).

    It's sad. Our neighbours to the south and north appear to be much more active and have a lot of fun playing radio.

    Just curious, what equipment do you have to check for spurious emissions of your VHF/UHF equipment? Good UHF wavemeters aren't that easy to build/come by, spectrum analysers beyond the financial reach of most, and wideband receivers probably not allowed ...

  16. #56

    Default Re: using walkie talkie on SMRT trains

    Quote Originally Posted by LittleWolf View Post
    QRPing. Preferrably QRP portable. I had lots of fun in the US talking to Europe with a few watts and a wire up the tree. That isn't much fun though if you have to tell IDA a week in advance when & where you're going to play radio - I want to operate spontaneously when conditions are good. And foxhunting - no fun if you have to declare your hideout ...

    Morse code isn't a problem (ok, I'll have to brush up, but 5wpm still can). More the requirements on antenna setups which pretty much mean you must have landed property to do anything using a fixed station. And the strict regulations that effectively prevent homebrewing and experimenting (apparently there's no exemption for homebuilt/modified equipment from type acceptance, which means $$$$ for getting them certified/tested).

    It's sad. Our neighbours to the south and north appear to be much more active and have a lot of fun playing radio.

    Just curious, what equipment do you have to check for spurious emissions of your VHF/UHF equipment? Good UHF wavemeters aren't that easy to build/come by, spectrum analysers beyond the financial reach of most, and wideband receivers probably not allowed ...
    I cannot morse at all, can't be bothered to learn because no one to practise with also.. That's why I got stuck with restricted license until they deregulate that.

    I didn't bother to check my equipment for spurious because they need to be inspected by IDA anyway. If I need to, I could always access my company's equipment. Just need to find a big attenuator. I do have a VHF VSWR meter though I prefer to use a VNA any time to measure the impedance of my antennas. I think my handheld is probably dead by now (haven't used it for many years) so I can safely say I don't have an equipment anymore. I did think of getting a HF set but thought it might be better to put the money into photography.

    The SARTS VHF repeater here is always plagued with QRM from the south.. many of them just operate without a license and use the VHF sets like a telephone.
    Last edited by lsisaxon; 3rd October 2007 at 01:19 AM.

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