A metal cage of the train acts like a Faraday's cage, which is probably why the signal loss might be significant.
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.
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.
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.Originally Posted by Astin
Last edited by firefly99; 27th September 2007 at 10:18 AM. Reason: additions
You should try it in a train that is not crowded with people.
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.
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.
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.)Understand talkies more than 4 or 5W requires IDA approval.
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.
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
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.
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.