[SOLVED] Need Help with Radio Frequency

[bugsbunnyboss]

Hi Everyone,

Can you send a signal(voice) that can be received across the world (i mean everywhere in earth)? if so, how? Please give a detailed answer.

Please forgive me for being naive if this is a very simple task.

 

[sky_123]

The question is too vague (since it is possible to make a phone call across the world, then it means the answer to your question is "yes").
If you want to do it with radio, then again it is too deep a topic, but this doc may help to understand how some things are possible.

 

[bugsbunnyboss]

The question is too vague (since it is possible to make a phone call across the world, then it means the answer to your question is "yes").
If you want to do it with radio, then again it is too deep a topic, but this doc may help to understand how some things are possible.

Thanks sky_123 for your reply and the document. I would read the material now.

The reason I asked this question is because I was watching die hard 4; where in a scene a guy would tune in to 666 MHz(which in the film is a hacker's freq) and then speak to him from quite a distance. So I was wondering if it was possible to hear to a channel (e.g.666MHz) from any part of the world and join in that conversation? If yes how and what are the frequency and power requirements? I browsed through certain materials and am assuming that lower the frequency; greater the distance. If this is the case then why people use HF,VHF and UHF for transmissions like FM,TV or govt services.

I hope now i made my question clear!

 

[sky_123]

I've not seen the 4th Die Hard yet : )
The different layers of the ionosphere have a lot to do with long-range comms, you'll
find lots of info on this on amateur radio websites such as **broken link removed**. It explains things like why you can hear so many radio stations at night sometimes on SW (HF) frequencies. It doesn't need a lot of power, a few watts would be sufficient. Even Voyager only transmits on low power apparently.
However, 666MHz is unlikely to be used for long-range comms, but you can transmit a lot using the bandwidth available at these higher freq allocations.

 

[enjunear]

For a basic answer, no. And certainly not at 666 MHz. The attenuation of a medium is given (in general) as:
\[Attenuation (dB) = \alpha * distance * frequency\] (see also, here)

As frequency goes up, the attenuation over a fixed distance also increases. So you can get EM waves to travel further at lower frequencies (like HF), than at higher frequencies (like S-band, 2.4 GHz)... all else being equal.

Additionally, when you talk to folks that deal with amateur radio (www.arrl.org), at low frequencies, you can get long distance transmission and reception, but you'll wind up with areas that the signal hits and other areas that it skips. Think of it like skipping a stone across water... where the stone touches the water, you'd be able to pickup the signal, where its in the air, you wouldn't get signal. Now envision the the radio waves bouncing off of the earth's surface and the ionosphere, which is reflective at low frequencies (and transparent at higher frequencies). One guy I knew in college used the HAM radio station to call a friend in Australia about once a month. From the math, the signals traversed up and down several times to get from North America, over the Pacific, and to Australia.