What would be the benefit of higher frequency transmission? I was browsing through a website looking at some parts and came across two transceivers, one operated in the 434MHz band and the other the 915MHz band. From my perspective, it seems that it would consume more power transmitting at over twice the frequency.

Link to the product: https://www.sparkfun.com/products/9582


If sending data, a higher transmission frequency means a higher data rate. Consider an FM transmission - it "deviates" a carrier between two different frequencies in the spectrum (\$f_0\$ for data 0 and \$f_1\$ for data 1) and, for a given frequency deviation (measured in hertz), the receiver is able make a more robust distinction between the two frequencies when there are more cycles of the carrier wave to detect.

On the other hand, at higher frequencies, the attenuation between transmitter and receiver is greater. This is known, due to work originally done by Friis. Link loss for a radio system is:

Link Loss (dB) = 32.4 + 20log\$_{10}\$(F) + 20log\$_{10}\$(d)

Where F is in MHz and d is distance between the two antennas (kilometres). This is the standard free-space link loss equation - there are anomalies at some frequencies that make it more effective to transmit at a higher frequency but this is a massive subject.

These are two reasons that I consider significant but, there are plenty more that are important. For instance, a higher frequency means smaller antenna size generally but, lower frequencies can be received, due to ionospheric effects at points on the earth well below the horizon (higher frequencies tend to be more-of-sight).

Given that we tend to be "running out of" clean and utilizable air waves (quicker than we are depleting our fossil fuels!), any disadvantage to using higher frequency is a moot point.

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