New topic. Double-checked example.

docs/reference/radio/received-signal-strength.md

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+# Received Signal Strength
+
+Find how strong the ``radio`` signal is, from `255` to `0`.
+(`255` means a weak signal and `0` means a strong one.)
+
+The micro:bit finds the signal strength by checking how strong it was
+the last time it ran the
+[receive number](/reference/radio/receive-number) function. That means
+it needs to run **receive number** first.
+
+### Returns
+
+* a [number](/reference/types/number) between `255` and `0` that means
+how strong the signal is.
+
+## Simulator
+
+This function only works on the micro:bit, not in browsers.
+
+### Example
+
+This example shows how strong the radio signal of the
+[light level sender example](/reference/input/send-number) is.
+
+```blocks
+let x = 0;
+radio.setGroup(99);
+basic.forever(() => {
+    x = radio.receiveNumber();
+    basic.showNumber(radio.receivedSignalStrength());
+});
+```
+
+### See also
+
+[receive number](/reference/radio/receive-number), [send number](/reference/radio/send-number), [on data received](/reference/radio/on-data-received)