Gain vs Distance
This information is approximate only as there are many things that affect path loss, however it does provide a good indication of the requirements for a given distance.
- Path Loss =
| Where d = distance (km) and  |
- Receiver sensitivity can be taken as -70 dBm. This means that the receiver has a gain of +70 dB. At this level the vision should be quite acceptable.
|
| | 1W | = +30 dBm | | 2W | = +33 dBm | | 5W | = +37 dBm | | 10W | = +40 dBm | | 12.5W | = +41 dBm |
|
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| Q) How much Tx antenna gain is required to transmit 35 km at 2.5GHz? | | A) Rx sensitivity = -70 dBm, Rx Antenna Gain = 20dB & Tx power = 1W |
|
 0.12 m
| |
- Path Loss
 131.3 dB
|
Gain
| Must Equal | Loss | | Rx Gain | +70 dB
| | Path Loss
| +131 dB
| Rx Antenna Gain
| +20 dB | | Fade Margin
| +0 dB | Tx Gain
| +30 dB
| | Cable Loss
| +0 dB
| | Tx Antenna Gain | +?? dB
| | I/P Filter Loss
| +0 dB
| | | 120 dB | | | 131 dB |
|
Therefore, Tx Antenna Gain = 11dB |
| In the real world, you need to take into account: | - Fade Margin |
| - Cable Loss |
| - Input Filter Insertion Loss |
