What changed
Receiver performance — edited Aug 31, 2026 by Unknown editor
This is the first recorded version, so every line is shown as added. Note: Imported from content/wiki
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Transmitters are easy: almost any modern radio puts out a clean 100 watts. Receivers are where
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radios differ, and where the specifications are written to be flattering. These are the numbers that
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predict how a radio behaves on a crowded band.
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## Sensitivity is rarely the problem
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**MDS** (minimum discernible signal), often quoted as noise floor in dBm, says how faint a signal the
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receiver can hear. Any current radio hears far below the atmospheric and man-made noise arriving at
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your antenna on HF, so sensitivity almost never limits you below 30 MHz — your noise environment
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does. See [RFI and noise](/wiki/station/rfi-and-noise).
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Above 50 MHz, where the sky is quiet, sensitivity and preamplifier noise figure start to matter, and
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a mast-mounted preamp ahead of the feedline loss can be worth several dB.
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## Dynamic range is the problem
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Dynamic range describes what happens when a strong signal is near a weak one:
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- **Blocking / gain compression** — a nearby strong signal desensitizes the receiver so the weak one
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fades.
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- **Third-order intermodulation (IMD3)** — two strong signals mix inside the receiver and produce a
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false signal where neither exists. The figure of merit is **IP3** (third-order intercept, in dBm);
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higher is better, and the useful test is at 2 kHz spacing, not the flattering 20 kHz.
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- **Reciprocal mixing dynamic range (RMDR)** — how much the receiver's own local-oscillator phase
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noise smears a strong nearby signal across your passband. On a contest weekend this dominates, and
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it is the number that separates good radios from great ones.
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The ARRL Lab and the Sherwood receiver tables publish these consistently measured; a manufacturer's
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brochure often does not.
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## Filters and the front end
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- **Roofing filters** sit early in the signal path in a superheterodyne receiver and limit how much
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energy reaches the later stages. A narrow (300–600 Hz) roofing filter is the single biggest
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contest-band improvement in a traditional radio.
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- **Direct-sampling SDRs** convert the antenna signal to digital immediately. Their limits come from
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the analog-to-digital converter's bit depth and the front-end preselector rather than crystal
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filters, which is why a good SDR can be superb but overloads abruptly rather than gracefully. See
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[software-defined radio](/wiki/station/sdr).
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- **DSP bandwidth, notch and noise reduction** operate after the damage is done. They make listening
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more comfortable; they cannot recover a signal that overload has already buried.
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- **Preselectors and band-pass filters** ahead of the receiver help enormously at a multi-station
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club site or Field Day setup where another transmitter is 100 feet away.
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## AGC, attenuators and using what you have
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The two most underused controls on any radio are the **attenuator** and **RF gain**. On a loud band,
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20 dB of attenuation costs you nothing you could hear anyway and moves the whole receiver back into
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its linear range. Setting AGC decay short for CW and long for SSB, and turning off noise blankers
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that are pumping on a strong signal, will improve reception more than most hardware purchases.