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The HP 423A (also referred to as Agilent / Keysight 423A) is a coaxial crystal detector. – Detector has been tested and is in working condition.
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It’s a 50 Ω device, designed for measurement in coaxial RF systems.
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“NEG” in the model name means negative output polarity. i.e. the detector’s diode is oriented so the output voltage is negative with respect to ground when receiving RF power.
Key Specifications
Here are some of the main specs of the 423A:
| Parameter | Value |
|---|---|
| Frequency range | 10 MHz to 12.4 GHz |
| Maximum input power | About 100 mW (≈ 20 dBm) continuous for the A version. |
| Input impedance | 50 Ω for RF input |
| Output impedance (load) | The output is shunted by a capacitor (~10 pF) and has a load resistor; output impedance is specified <15 kΩ |
| Sensitivity / square-law region | The detector behaves in the square-law region (output voltage ∝ input power) for relatively low RF power, depending on load, etc. The threshold for leaving square-law behavior depends on output load impedance. |



