Transmit Range in a building?

Hello

I have a TX and RX module at 433.9MHZ,I want to add PA to output of TX module to increase range(it have +4dbm power output without external PA)

For 500 meter range in a building how much power output is needed? Is 50mW enough? Is other frequecies like as 315MHZ,900MHZ or 2.4GHZ better?

It depends on the building. In some cases 5w is not enough to get 500m.

There are two problems.

Multipath reception. UHF signals bounce around in buildings. This can help the range but it gives peaks and nulls in coverage. The radio waves can arrive directly and bounce off metal objects. If a direct wave and a reflected wave arrive 180degrees out of phase and are similar in strength they cancel out and reception is bad at that point but 30cm away where the waves add. This is why wifi access points have two antennas.

Path loss. Radio waves are attenuated by objects like walls and people.

My experiance of using 0.5Watt 446MHz radios in tall buildings is that the range is often much less than 500m. When someone is in the basement and someone is on the 40th floor, only 200m in a straight line, they don't work. The radio signal just dosn't go through 40 layers of concrete and steel.

Radio equipment that people carry in pockets has problems with the human body absoring some signal and detuning the antenna.

It may work better if you can have the transmitter at a suitable height on another building so that the radio signal can go in the windows instead of having to go through the floors.

One mistake I have seen is to have a high gain antenna on top of the building that is sending most of the power towards the horizon instead of down into the building.

Many big buildings have "leaky feeder" coax run up cable risers so that repeater equpipment can pick up walkie talkies throughout the building.

Sometimes putting radio equipment close to cables that run through a building helps carry the signal.

315Mhz may work better in some cases, it may be attenuated slightly less but it dosn't bounce around as much.

900Mhz might work slightly better if you put the transmitter outside the building and use and antenna with some gain to beam the signal in the windows.

You are likely to find that there are many other transmissions on 2.4GHz that will block your signal.