Do different frequencies have different capabilities?

Question

I read that google was planning on purchasing a spectrum from the Fcc and they were going to use it to transfer data. I was wondering if the value of the frequency affects the data that is being transfered (ex. Higher the frequency the more data you can send)?

Answer 1

The amount of data which you can transmit is generally determined more by the bandwidth which you are allocated than by the actual frequencies of the band. However, allocations at higher frequencies tend to be larger than allocations at lower ones. An allocation up in the GHz range might be 50 MHz wide; while the comparably sized range from 50-100 MHz is definitely not going to be licensed to a single use or company.

However, the amount of data which can be transferred in a given bandwidth also depends on the signal to noise ratio, and that can have some frequency dependence, either on power of the signal or on the power of the interfering noise.

• Some frequencies are more attenuated than others - for example, if there's a resonance with water molecules in the air

• Some frequencies propagate further into structures than others

• Generally it is easier to make high gain antennas at smaller frequencies, since the antennas can be a of significant size in relation to a wavelength (however, at extremely high frequencies geometric imperfections in the antenna become an issue)

• It's hard to make an antenna work optimally over more than a small fraction of its center frequency, hence it's easier to make an antenna that covers a wide absolute bandwidth at high frequencies than it is to make one which covers the same bandwidth at lower frequencies

• Noise sources (natural, distant transmitters, unintentionally radiating electronics, etc) are more prevalent at some frequencies than others due to physics, propagation, usage traditions, etc.

• Frequencies below a certain limit are reflected off the ionsphere back to the ground, with the limit depending on the actual degree of ionization at any given time/altitude/location as influenced by the sun and occasionally other sources (objects re-entering from space, etc). As a positive, this can enable intercontinental communication with tiny amounts of power; as a negative it can cause interference between distant uses.