Interactive link budget — Friis with live margin

The Link Budgets tab is an interactive Friis-equation calculator. It tells you whether a planned link will close, at what margin, and what data rate is achievable.

Inputs (live recompute on every change):
- **Tx side** — power (dBW), antenna gain (dBi), feed loss
- **Path** — distance (km), frequency (GHz) — these set free-space path loss
- **Atmosphere** — rain/clouds/ionosphere attenuation (band-dependent presets)
- **Rx side** — antenna gain (dBi), system noise temperature (K), feed loss
- **Modulation/coding** — BPSK / QPSK / 8PSK / 16APSK with FEC rate; sets required Eb/No
- **Required data rate** — bps you need to push through

Live outputs:
- Received carrier power (dBW)
- C/No
- Eb/No achieved vs required
- **Margin (dB)** — green ≥3 dB, yellow 0–3, red <0 ("link does NOT close")
- Achievable rate at your minimum margin

Save the budget as a named record so you can re-open it during ops planning. Wally tool `comms_linkBudget` accepts the same inputs in chat for quick "will this work?" questions.