FAST Radio Telescope: Collecting Area & Signal Detection

Target signal

Source strength 10

Source distance 5.0

Dish diameters

Reference dish

25 m

FAST

500 m

Collecting area

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Collecting area

–

FAST area advantage

–

Detection readouts

SNR · reference

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SNR · FAST

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Why area wins

A dish's collecting area grows with the square of its diameter, and the received signal power scales directly with that area:

A = π(D/2)²
SNR ∝ A · S / d²

S is the source's intrinsic strength and d its distance — signal flux falls off as 1/d². FAST's 500 m dish has 400× the collecting area of a 25 m dish, so it can confidently detect signals 400× fainter, or from roughly 20× farther away, than the small dish can pull out of the noise.

SNR below ~3: signal is indistinguishable from noise
SNR 3–7: marginal, needs more integration time to confirm
SNR above ~7: confident detection

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Reference dish (25 m) FAST (500 m) Distant radio source

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Reference dish · 25 m

Ambiguous

SNR –Noise floor 1.0σ

FAST · 500 m

Confirmed

SNR –Noise floor 1.0σ