Re: How did they communicat ?

mowhoong wrote:
During my school days about 35 years ago, we were taught in our
physics lessons, the radio wave only travels or reflect in our
atmosphere when we listen to FM/AM ,CV band, Air band boardcast. But
I am curious to know how the radio wave communicate to the satellite
as air
do not even exist in space, this is just like vacuum space. Can any
kind soul out there explain? Thank you very much.
Regards

All frequencies of radio waves travel, without loss, through the vacuum of space. But the atmosphere traps some bands of frequency in a waveguide effect, near the surface of Earth. Those frequencies allow long distance communication around the curvature of Earth, but are poor choices for communication between surface and space. But even these frequencies leak out into space, to some extent, especially when launched near the vertical. Here is a paper that goes into more detail:
http://www.ips.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Intro%20to%20HF%20Radio.pdf

But there are lots of frequency choices that are not reflected much by the atmosphere, but travel essentially in a straight path through it into space, and back from space.
.

Relevant Pages

  • Re: radio mics
    ... - UHF 8channel F Band ... A licence is not required for wireless microphones on UHF frequencies ...
    (rec.music.makers.saxophone)
  • Re: Voice of Russia
    ... your radio indicate to me that you may be new to the hobby. ... frequencies in the 31-meter band and the 22-meter band. ... that there are no world band transmissions at all between 14900 kHz ... Some frequencies come in better than others. ...
    (rec.radio.shortwave)
  • Re: What Spectrum is Available from 30 MHz to 120 MHz?
    ... My guess is that the militairy needs all kinds of frequeny-ranges as they have all kinds of very different applications: ranging from telecommunication, over radar and satellite to jamming; and both a short-range to very long distance. ... Another element is that the militairy use spread-spectrum and frequency-hopping systems for "stealthing"-applications and the more frequencies you can hop to, ... The only other application in that region is EPIRBs between 121.45 and 121.55 Mhz (beacons used for maritime safety, which start broadcasting a signal when dropped in the water which then can be picked up by the SARSAT satellites). ... My guess is that there will be a discussion first in the CEPT/ERO on what to do with band I after the shutdown of the PAL-services overthere. ...
    (alt.radio.digital)
  • Re: Expert tears DAB to pieces in Norwegian newspaper
    ... squeeze as much capacity as possible out of the band. ... This NSFN are clearly using different frequencies. ... heavily with 7 MHz channels subdivided into the famous four sub ... the result is a lack of DAB allocations in 2006. ...
    (alt.radio.digital)
  • Re: low pass filter between vfo and mixer
    ... So, VFO frequencies should be: ... i do not see why you would want to put a low pass filter ... but a ham band only receiver, IMHO, it is a much better idea to put ...
    (rec.radio.amateur.homebrew)