Offline wtbofnc

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Ionosphere
« on: January 17, 2016, 09:45:35 PM »
https://en.wikipedia.org/wiki/Ionosphere


Can anyone elaborate on this?  Why are Satellites needed?

« Last Edit: January 17, 2016, 10:00:16 PM by wtbofnc »

Offline CableDawg

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Re: Ionosphere
« Reply #1 on: February 06, 2016, 01:12:21 PM »
From the linked article:

"Thanks to the property of ionized atmospheric gases to refract high frequency (HF, or shortwave) radio waves, the ionosphere can be utilized to "bounce" a transmitted signal down to ground. Transcontinental HF-connections rely on up to 5 bounces, or hops."

Depending on where the signal originates and where it is received the loss (due to the number of bounces required) would be too much for consistent, mass communication as well as there not being enough bandwidth to support the shear amount of worldwide communication.

Another aspect is the physical limitations of the equipment.

HF (frequency 3-30 Megahertz) has a wavelength of 10-100 meters.  This means that an antenna of 10-100 meters would be needed to transmit and receive the information.

Satellite communication operates on a frequency of 1-40 Gigahertz.  This means that an antenna of 1-10 centimeters would be needed to transmit and receive the information making it a much more viable for mass communication.

To give a more concrete example, cell phones work on a frequency between 800 Megahertz and 1.3 Gigahertz giving an antenna length of between 20 and 40 centimeters (7-14 inches).  That antenna is packaged inside cell phones (unless you have an older phone with an external antenna).  To communicate, via cell phone, with HF each phone would have to have an antenna between 10 and 100 meters (33-330 feet)  long.

This applies equally to FE as to RE simply because, even on FE, you have to account for obstructions such as mountains and antennas work best with direct line of sight.