# Why an antenna cannot receive analogue baseband signal of 0-4000Hz?

1. Sep 5, 2009

### dandeliondrea

Modulation is the process of impressing an information bearing signal to a carrier for effective transmission over a long distance. example Am and FM used in radio transmission

Analogue baseband signals of 0-4000Hz are shifted to 60-64Khz range.

Communication systems often do not carry signals in baseband (with the exception of local loop)

Wavelength of a radio wave in free space is the speed of light/the frequency.

That means a 4KHz voice signal has a wave length of 75000m (300000/4). We cant possibly make an antenna to receive such signals

Why an antenna cannot receive analogue baseband signal of 0-4000Hz?
I heard we need a very large antenna to receive analogue baseband signal of 0-4000Hz? why?

2. Sep 6, 2009

### Born2bwire

If you want to send out a signal a 4 KHz, then yes, for the most part we can't make a resonant antenna due to the size constraints (but take a look at the naval ELF submarine antennas). However, by modulating the frequency at a much higher carrier frequency, then we only need to receive at the carrier frequency. So if the carrier frequency is say 62 KHz, then we can design an antenna, but it will still be friggin huge. I think MHz would be a better starting band for carrier frequencies as we have seen with radio and television standards.

3. Sep 6, 2009

### Katze

You have to have an antenna to detect or receive electromagnetic radiation and information carried by it. A receiving antenna can be a piece of wire, or even your own finger.

Pull out your Sound Blaster plug and rub the tip with a finger. You should be able to hear mains noise in your loudspeakers.

An other way of demonstrating this is touching an oscilloscope probe tip with your finger. You should be able to see mains frequency and much more.

How much voltage your antenna generates, depends on the field strength and the size and shape of the antenna.

4. Sep 6, 2009

### dandeliondrea

Thanks for the explanation.

5. Sep 7, 2009

### Andy Resnick

Another way may be to note that in antenna design, making the frequency spread $$\Delta\omega/\omega$$ small makes the design easier to implement.

6. Sep 8, 2009

### dandeliondrea

i see, thanks for the information.