Early Satellite communications use frequencies below to 1 MHZ due to the state of art of technology. However, with the advance of new technologies, it was possible to use higher bands. The use of ten of MHZ is due to the next considerations:
- Today communications are hungry of higher bandwidths, so the use of higher bands of frequencies.
- The higher frecuencies the lower power to reach the satellite.
- The lower power the smaller satellite dish antenna you will use, so the cost is lower.
- But, the higher frequencies, the higher attenuation due to the space free losses. However, the power is still lower compared with lower frequencies.
These are some considerations in this field, if you need further information contact me to omargtg@yahoo.com and I'll give you public literature where you will get more informated.
Other reason is the size of wavelength with respect to frequency.
Wavelength is inversely proportional to frequency, therefore low frequency possess longer wavelengths than high frequencies.
What is the significance of this?
Between satellite and earth station, we have this ionosphere. Frequencies from VLF to HF are affected by this ionosphere. The layers of the ionosphere refract these frequencies back to earth. Frequencies in the bands of VHF, uhf and higher bands tends to pass thru' the ionosphere, therefore it can scape to the space to reach the satellite in its orbit.
The ionosphere is affected by the solar activity of the sun. The displacement of one ion to the other in the ionosphere is enough for wavelength of the VHF and higher frequencies to pass thru, unlike the wavelengths of HF down to VLF.
