If you want a receiver with 20 MHz instantaneous bandwidth, there are only a few realistic options — and one stands out as the simplest choice.
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Best simple answer
✔ HackRF One
HackRF One
Bandwidth: up to 20 MHz real-time
Frequency range: ~1 MHz to 6 GHz
RX + TX (half duplex)
Very widely used for exactly this requirement
It is the cheapest and most direct way to get a true 20 MHz-wide view of spectrum in one shot.
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Important performance note (for radio astronomy use)
While HackRF does meet the bandwidth requirement, it has limitations:
8-bit ADC → higher noise floor than scientific SDRs
No front-end filtering → more strong-signal distortion
Lower dynamic range → can struggle near strong broadcasters
So it works for bandwidth, but it is not ideal for sensitive hydrogen-line work unless carefully filtered and pre-amplified.
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Better (but more expensive) alternatives
If you want 20 MHz bandwidth with much better radio performance:
USRP class SDRs
USRP B210
20 MHz is easy for it (and much more)
12-bit ADC → much better dynamic range
Designed for scientific / engineering work
ADALM-Pluto (modified)
ADALM-Pluto SDR
Can do ~20 MHz class bandwidth
Much better linearity than HackRF
Cheaper than USRP, but still limited in dynamic range
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Practical recommendation (for your hydrogen-line / interferometry work)
If your goal is radio astronomy rather than just “seeing 20 MHz of spectrum”:
✔ Best budget 20 MHz: HackRF One
✔ Best scientific choice: USRP B210
✔ Best compromise lab SDR: PlutoSDR (modified, external clock)
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Key reality check
At 1420 MHz:
Hydrogen line only needs ~1–5 MHz of clean bandwidth
20 MHz is mainly useful for:
RFI monitoring
Doppler survey over wide velocities
Multi-source context
So in practice, bandwidth is not your limiting factor — dynamic range is.