Simple No-Tune Wi-Fi Sniffer
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 Description Here is a circuit of a very basic No-Tune Wi-Fi Sniffer. It’s about as simple as it gets, using only two transistors. It could detect my notebook at 10 feet with a tiny vertical. No doubt, a Well Tuned Dipole would increase it’s range.
Q1+Q2 are RF amplifier stages tuned to receive 2.4 – 2.5 GHz. L1+L2 are molded chokes. The critical components are L1, C3, L2 and C6.
LED1 is the signal indicator. As you approach a signal source, the LED [1.3v], will become brighter. It’s most useful in dim to dark areas, this is due to lack of current, however, there are now more efficient LED’s available, so it may be useful during full daylight. Alternatively, you could use an old VU, or MA DC meter instead of a diode.
The needle will gradually rise as you approach the signal source. 50K potentiometer should be placed across the meter and adjusted near a Wi-Fi for Full Scale. The sniffer should be built into a metal box to minimize hand capacitance and stray RF effects.
For the imaginative, a Low Current DC Buzzer could be used.
Be aware that most strong RF signals can produce a reading. Harmonics from mobiles, portables, CB's, microwave ovens, and even mobile phones, or their towers are among the most common causes. Either way, it will indicate weather it’s worth while or not to open your notebook and check out a signal.
Designer & Author: Special thanks to Laszlo Kirschner.
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