attenuation-distance-frequency 1

[Martintin]

Hi,

My name is Martin Aureliu and i'm quite new in the radio communications field.

I know that the propagation losses vary with distance having the frequency as a parameter but I don’t manage to find an appropriate chart for this.

Could you please tell me where may i find a chart for distance - attenuation - frequency relationship for VHF and UHF?

Thank you!

 

[JohnFortier]

Martin,

As I recall, the formula is 34.4dB + 20 log10 D + 20 log10 F. = Loss

D is in Kilometers and F is in Megahertz

This will give you a propagation loss figure in dB. To this you should add your transmit power in Dbm, your antenna gains and any co-ax or waveguide losses.

Together these will give you a figure for the received power at your receiver in dBm. If this exceeds yor receiver's minimum sensitivity, you will probably, repeat probably, have a good link.

This also assumes a clear line of sight and no reflective fades or other Freznel zone nasties.

Directional antennas improve performance markedly, with the gain of a dish antenna actually increasing as your frequency increases, offsetting somewhat the 20 log10 F term in the propagation loss equation.

Hope this helps

John

 

[RudyL54]

Question about microwave line of sight antennas. Probably easy to some.

Why do you think the shape of microwave antennas made like a drum? I know that a certain material need to enclose the feed for protection due to harsh environment but why like a shape of a drum?

Any ideas?