# Use of high frequency in communication

1. Oct 25, 2012

### amaresh92

can anyone tell me why do we use high frequency in communication? why we cant just use low frequency signal for these ?

2. Oct 25, 2012

### Averagesupernova

You need to be more specific. How high do you consider high frequency and how low do you consider low frequency? We DO use low frequencies (baseband audio for instance) for communications. An intercom connected with wires would use this type of scheme. Are you concerned with wireless?

3. Oct 25, 2012

### Jay_

My guess is that they require less antenna height and are not as easily attenuated. And I guess that is because they have higher energy ( E = hf ). But I would like an expert to comment.

4. Oct 25, 2012

### vk6kro

This is mostly a result of the properties of the ionosphere.

This varies from time to time (and sometimes from minute to minute), but frequencies between about 2 MHz and 30 MHz can be reflected from the ionosphere and travel around the curvature of the earth.

So, quite large distances can be covered.

Above 30 MHz (again this varies), signals tend to go straight through the ionosphere into space. So, they are mostly lost unless they hit the moon or something else and get returned to earth.

This is not a bad thing if you want to have TV stations in different cities and not have them interfering with each other.
If you want to have police or ambulance or taxi signals that stay in one area, you would use frequencies above 30 MHz, and usually above 100 MHz.
This means the same frequencies can be used in different areas without them interfering with each other.

On the frequencies between 2 and 30 MHz, some frequencies perform better than others at different times of the day, for different distances, so this is used to optimize communication.
This is the "short wave" band which is probably less important now than it used to be. Transmissions here are strictly controlled (as they are on all frequencies) so that the high powered signals do not interfere with each other.

The frequencies below 2 MHz are used for local AM radio broadcasts and other transmissions where the lack of long distance transmission is an advantage.

5. Oct 25, 2012

### Floid

There are a lot of different reasons.

The biggest reason is that a higher frequency have a potential for higher bandwidth.

Other reasons are that as more and more thing use wireless communications we are naturally forced to higher frequency to find unused space.

Also, higher frequencies allow for smaller antennas.