How Does an NLJD Work?
The operation of a Non-Linear Junction Detector (NLJD) is based on illuminating a specific object with high-power RF energy (either continuous wave or pulsed). The NLJD then receives the re-emitted response from the object at multiples of the probing signal's frequency, known as the second and third harmonics.
Key Points:
1. Detection of Hidden Electronics:
- The NLJD detects hidden electronics using the non-linear properties of semiconductors.
- Electronic devices contain components like printed circuit boards (PCBs) with conductors and semiconductor elements (diodes, transistors, microchips).
- These elements act as non-linear reflectors for the high-frequency probing signal.
2. Probing Signal Interaction:
- The high-frequency signal induces an alternating electromotive force (emf) in the conductors, which is converted by the non-linear elements into RF signals at multiples of the probing frequency (harmonics).
- These harmonics are re-emitted into space and detected by the NLJD's receivers, which are tuned to these frequencies.
3. Identifying Electronics:
- Detection of second and third harmonics indicates the presence of a hidden electronic device, regardless of whether it is powered on or off.
- Generally, if the second harmonic's level is higher than the third, the detected object is assumed to be artificial (electronic).
- If the third harmonic is higher, the object is considered a natural non-linear junction, like a metal-oxide-metal (MOM) element.
4. Spectrum Analysis for Clarity:
- This identification isn't always accurate, for instance, a rusty metal object may also show a higher second harmonic level.
- Additional methods like harmonics spectrum analysis can help. Applying physical impacts (e.g., knocking) on the object while observing the spectrum can provide more clarity.
- Natural objects will show spectrum widening under physical impact, while artificial objects remain largely unchanged. During demodulation, this manifests as a rustling noise in the headphones when the spectrum widens.
By simplifying the NLJD operation principles, we aim to make it easier for you to understand how this sophisticated tool can detect hidden electronic devices effectively.
