Why Power Falls with Range
- Same transmitted power, larger spherical area:
- : area ×4, flux ÷4
- Range ×10 → area ×100 → (see useful decibel relationships)
Calculating Free-Space Path Loss
Free-Space Path Loss
- In km and GHz:
- With in m and in GHz the constant is 32.45 instead (used in Class 3); Class 4 rounds 92.45 to 92.4
- is a positive loss; subtract it in the power ledger (received-power equation)
- At one frequency, free-space loss changes only because range changes
- It also grows with frequency (for a fixed range) — but so does the gain of fixed apertures: Frequency Selection
TERPSat: The Edge Cost
- Overhead, :
- At 5° elevation, (slant range):
- Edge cost: — the price of serving the low-elevation edge of the pass
- Deep-space scale: Voyager 2 at about km gives (Homework 2)
- References: ITU-R P.525-4 (2019) and P.525-5 (2024), Calculation of Free-Space Attenuation