The relation between frequency and range of wireless device

[aryajur]

Frequency and Range

What is the relation between frequency of operation and its range of a wireless device? Is it true that the range would decrease as we increase the frequency?? Doesn't it depend on the power of the transmitter.
If using a higher frequency does utilize higher power, what kind of frequency is used in communication with satellites or even with the Mars Rover???
Another question is if using higher frequency does increase the power then as I keep hearing that FCC has just opened up frequencies in the high GHz range for commercial applications, what good would those frequencies be??? I mean where could they be used???

 

[House_Cat]

Re: Frequency and Range

You ask a lot in one breath. I'm going to leave out lots of detail to just hit the high points.

As frequency increases, the signal is absorbed more by physical objects (atmospheric moisture, trees, buildings, etc). Hence you need more power to make up for the signal loss. For constant power, the range decreases because the signal losses increase with increasing frequency. This energy transfer to physical objects is the principle behind microwave ovens which operate at 2.45Ghz. and transfer the transmitted energy to water molecules in the food.

Another factor affecting terestrial communication range is the tendency of low frequencies to follow the curvature of the earth's surface by reflecting off of atmospheric layers or refracting through atmospheric layer boundaries. This allows for very long distance communication at low frequency. As frequencies get higher, the tendency is for the signal to pass through the layer boundaries rather than reflect, and refraction angles tend to lessen. The result is shorter range, and increasing power won't help - all you're doing is blasting a signal into space.

Satellites don't require huge amounts of power because they are line of sight to the receiving antenna (no trees, mountains, buildings, etc to penetrate). The distance is great, but the only losses are in the atmosphere itself - mostly due to moisture.

The higher frequencies are useful for the same things as lower frequencies. You just need to approach the problem from a different viewpoint. For example, your cell phone is low power, high frequency. The range of the phone is worldwide because the phone only has to reach the nearest cell tower, which then relays the signal to another cell tower or to a satellite. In other words, you don't need high power, you just need to relay the low power signal from one low power transceiver to another - this can be repeated hundreds of times, if necessary, to reach the destination. Another good example is your wireless LAN connection. It only has to reach tens of feet to relay to the internet for worldwide communication.

Power is not as important as ingenuity in communicating at high frequency. Different modes of modulation, burst transmission, signal relay, etc, all get the job done without huge amounts of power.

 

[brew]

Re: Frequency and Range

You ask a lot in one breath. I'm going to leave out lots of detail to just hit the high points.

As frequency increases, the signal is absorbed more by physical objects (atmospheric moisture, trees, buildings, etc). Hence you need more power to make up for the signal loss. For constant power, the range decreases because the signal losses increase with increasing frequency. This energy transfer to physical objects is the principle behind microwave ovens which operate at 2.45Ghz. and transfer the transmitted energy to water molecules in the food.

Another factor affecting terestrial communication range is the tendency of low frequencies to follow the curvature of the earth's surface by reflecting off of atmospheric layers or refracting through atmospheric layer boundaries. This allows for very long distance communication at low frequency. As frequencies get higher, the tendency is for the signal to pass through the layer boundaries rather than reflect, and refraction angles tend to lessen. The result is shorter range, and increasing power won't help - all you're doing is blasting a signal into space.

Satellites don't require huge amounts of power because they are line of sight to the receiving antenna (no trees, mountains, buildings, etc to penetrate). The distance is great, but the only losses are in the atmosphere itself - mostly due to moisture.

The higher frequencies are useful for the same things as lower frequencies. You just need to approach the problem from a different viewpoint. For example, your cell phone is low power, high frequency. The range of the phone is worldwide because the phone only has to reach the nearest cell tower, which then relays the signal to another cell tower or to a satellite. In other words, you don't need high power, you just need to relay the low power signal from one low power transceiver to another - this can be repeated hundreds of times, if necessary, to reach the destination. Another good example is your wireless LAN connection. It only has to reach tens of feet to relay to the internet for worldwide communication.

Power is not as important as ingenuity in communicating at high frequency. Different modes of modulation, burst transmission, signal relay, etc, all get the job done without huge amounts of power.

may i just ask a few that i didn't get

based on what you said, with constant power, increase in frequency doesn't necessarily mean longer range for devices to communicate, right? if this is the case, if i use 915Mhz instead of the typical 2.4Ghz in a wireless keyboard the range will not be affected? and if the range is not affected, what other parameters would be affected given the change in frequency? thanks

 

[chuckey]

Power X antennae efficiency = ERP (effective radiated power). So for a given ERP, higher frequencies require smaller aerials. For instance a quartewave dipole at 2.4 GHz is about .12m (12 cm) at 900 MHz its .33 m So at the lower frequency the aerials needs to be bigger or its less efficient, but the power amplifier is easier to build/cheaper also the receiver. You takes yer money and yer makes yer choice
Frank

 

[saif haider]

a hypothetical radiating element will transmit equally in all direction but we can increase its radiation in our desired direction by using different techniques like phase shifting and using reflector to divert in one particular direction and increase its gain. Also, by making the power constant and also frequency using reflector like dishes or introducing elements we are able to transmit with more power deep into space and can also be able to receiver signals from deep space mission. the standing wave ratio for transmitters, which will effect in gain of antenna, could be resolved with the impedance matching techniques.