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I'm hoping someone here can sanity-check me on a distinction I keep arguing about with a colleague, because I think a lot of SDR specs are misread.
A typical integrated wideband transceiver is specified with: - Tuning (LO) range: 70 MHz to 6 GHz - Maximum instantaneous bandwidth: 56 MHz - Sample rate at that bandwidth: up to 61.44 MS/s, 12-bit
These describe two unrelated things:
1. Tuning range = every carrier frequency the LO can be set to. It is a set of reachable destinations, not simultaneous coverage.
2. Instantaneous bandwidth = the width of spectrum digitized in one capture, with no retune. The "70 MHz–6 GHz" part does NOT mean the device receives 5.93 GHz of spectrum at once. At any moment you see one window up to 56 MHz wide. To cover the full range you retune the LO and capture adjacent windows.
Why it matters:
- Probability of intercept: if you are scanning by retuning, a pulse shorter than your dwell + lock + calibration-settle time can be missed entirely. The window width and the hop time together define POI, not the tuning range.
- Continuous narrow-band services (voice, a known channel) need only a small IBW; a 200 kHz–few MHz window is fine and far cheaper to process.
- "Full-band sweep" is a sequence of ≤56 MHz captures stitched in software. Each retune also restarts the tracking calibrations (DC offset, LO leakage, quadrature), so fast hopping has a real settling cost.
Worked intuition: at 56 MHz IBW, covering a 1 GHz span needs roughly 18 adjacent windows, ignoring overlap — and every window pays a retune/settle penalty. At 20 MHz it is ~50.
The load side: widening IBW raises the sample rate, the digital interface throughput, and real-time DSP. Narrowing it lowers load but raises hop count and miss probability.
When you size a radio, the decisive questions are: what is the widest continuous slice I must capture at once, and what is the shortest event I cannot miss? The tuning range tells you where; the instantaneous bandwidth tells you whether the signal actually fits through the window.
Grateful for corrections or real-world POI numbers from folks who've built scanning receivers.
(Disclosure: I work on RF/data-converter applications, including AD9361-class transceivers — posting here to discuss the engineering, not to sell anything.)
A typical integrated wideband transceiver is specified with: - Tuning (LO) range: 70 MHz to 6 GHz - Maximum instantaneous bandwidth: 56 MHz - Sample rate at that bandwidth: up to 61.44 MS/s, 12-bit
These describe two unrelated things:
1. Tuning range = every carrier frequency the LO can be set to. It is a set of reachable destinations, not simultaneous coverage.
2. Instantaneous bandwidth = the width of spectrum digitized in one capture, with no retune. The "70 MHz–6 GHz" part does NOT mean the device receives 5.93 GHz of spectrum at once. At any moment you see one window up to 56 MHz wide. To cover the full range you retune the LO and capture adjacent windows.
Why it matters:
- Probability of intercept: if you are scanning by retuning, a pulse shorter than your dwell + lock + calibration-settle time can be missed entirely. The window width and the hop time together define POI, not the tuning range.
- Continuous narrow-band services (voice, a known channel) need only a small IBW; a 200 kHz–few MHz window is fine and far cheaper to process.
- "Full-band sweep" is a sequence of ≤56 MHz captures stitched in software. Each retune also restarts the tracking calibrations (DC offset, LO leakage, quadrature), so fast hopping has a real settling cost.
Worked intuition: at 56 MHz IBW, covering a 1 GHz span needs roughly 18 adjacent windows, ignoring overlap — and every window pays a retune/settle penalty. At 20 MHz it is ~50.
The load side: widening IBW raises the sample rate, the digital interface throughput, and real-time DSP. Narrowing it lowers load but raises hop count and miss probability.
When you size a radio, the decisive questions are: what is the widest continuous slice I must capture at once, and what is the shortest event I cannot miss? The tuning range tells you where; the instantaneous bandwidth tells you whether the signal actually fits through the window.
Grateful for corrections or real-world POI numbers from folks who've built scanning receivers.
(Disclosure: I work on RF/data-converter applications, including AD9361-class transceivers — posting here to discuss the engineering, not to sell anything.)
