Build a complete link budget in the sandbox, and predict — before you read it off the screen — the received power Prx that arrives, the link margin over the receiver's sensitivity, and whether the link closes.
A link budget is one line of addition in decibels: the received power is Prx = Ptx + Gtx - Ltx - PL + Grx - Lrx — everything the transmitter puts out, plus the antenna gains, minus every loss and the path loss. The link closes when that Prx exceeds the receiver's sensitivity, and the headroom between them is the margin = Prx - sensitivity. Reading the received power, the margin and the verdict off a real budget is how an engineer knows a link will work before a single antenna is raised.
Open the sandbox and pick the Office WiFi 2.4 GHz preset from the scenario dropdown — it reproduces the worked WiFi example of M9-L4 exactly. Each step names the one thing to read or the one preset to switch to; leave everything else alone.
Scenario preset -> Office WiFi 2.4 GHz Ptx -> 20 dBm
Distance d -> 15 m (switch to the Cellular downlink preset only in Step 3)
Watch the received-power readout Prx in dBm, the margin readout in dB, and the verdict tag — every number you predict is printed there.
With the Office WiFi 2.4 GHz preset, the budget adds Ptx = 20 dBm and the antenna gains, then subtracts the feeder loss, the path loss and the receiver losses. Predict the received power Prx = Ptx + Gtx - Ltx - PL + Grx - Lrx, then read the received-power readout.
The received-power readout is Prx = -56.83 dBm — the 21.5 dBm of EIRP, minus the 75.33 dB of path loss, plus the receiver gain and minus its losses. This is exactly the sum the demo's budget accumulates, term by term.
The receiver's sensitivity for this preset is S = -74.96 dBm. The link margin is margin = Prx - S, and the link closes only when the received power exceeds sensitivity. Predict the margin, then read the margin readout.
The margin readout is margin = Prx - S = -56.83 - (-74.96) = 18.13 dB — the received power sits 18.13 dB above sensitivity, so this WiFi link closes with healthy headroom.
Switch to the 900 MHz cellular downlink preset — a base station reaching a handset over Hata path loss. Predict the margin Prx - S for this link, then read the margin readout and the verdict tag.
The margin is Prx - S = -82.42 - (-106.64) = 24.22 dB — the received power exceeds sensitivity by a healthy 24.22 dB, so the downlink closes and the verdict tag reads LINK CLOSES. The link closes exactly when received power exceeds sensitivity.
Everything above is waiting in the sandbox. Drag the distance and watch the margin fall until the verdict flips from LINK CLOSES to NO LINK, add transmit power or antenna gain and watch it flip back, and switch between the WiFi, cellular, LTE, LoRa and mmWave presets to see which links close and which fall just short.
- Added up a WiFi link budget to a received power of Prx = -56.83 dBm
- Found the margin over sensitivity, Prx - S = -56.83 - (-74.96) = 18.13 dB
- Switched to the cellular downlink and read a 24.22 dB margin — the verdict LINK CLOSES is exactly received power exceeding sensitivity
- Every value you predicted is the demo's own link-budget arithmetic, not a picture