将天线连接到计算机的 USB 端口

Question

I have some basic theoretical background in RF. These are the main questions I've been asking myself:

• Consider a WiFi adapter connected to a USB port of a computer. Does the time-varying voltage wavefront undergo de-modulation and then only the digital signal is piped into the USB port? If yes, then probably there is no simple way to pipe the GHz analog signal into the USB port because the electronic components and circuits are not designed for such high frequencies (just throwing some thoughts here!) If you are 100% positive that one cannot use a PC to receive the time-varying de-modulated analog voltage signals, please ignore the below questions.

• what component is needed to interface a (say 2.4 GHz) monopole antenna to a USB port? Should I worry about impedance matching with the usb port (does this sentence even make sense)? My goal is not just ordering the component but also gaining a robust textbook-level understanding of the basic principles of interfacing RF components with electronics and the limitations.

• what Python library should I use to store, analyse and process the time-domain analog voltage signal that is being piped into that USB port?

Thanks

Answer 1

Unfortunately there's not a USB dongle that is capable of performing the first part. You will need some serious test equipment to capture a significant chunk of 2.4 GHz signal that is found in WiFi communications.

To provide more detail, once the modulated signal is received by a WiFi device, it will go through several stages of analog and digital processing. Once the physical signal has been processed, various layers of the device's firmware will perform operations to produce data packets. These packets are used by different layers of the firmware stack. By the time any data is sent over the USB bus, it will be very different from the de-modulated voltage that it was originally encoded in.

I am more familiar with BLE than WiFi but I have found BLE a very interesting protocol to work with and study. The spec is free ( BLE 5.2 Spec ) but (as with any communication protocol) can be very dense, but it provides a lot of detail as to how the protocol is designed. My experience is that using a cheap BLE sniffer (such as nRF BLE Sniffer ) + Wireshark if you're interested in the protocol aspect of a wireless protocol.

If you're really after capturing the analog signal, your best bet is to find the best oscilloscope you can get your hands on (high bandwidth and sampling speed), attach a 2.4 GHz antenna and capture the modulated signal. I believe various oscilloscope vendors sell packages for capturing/decoding WiFi signals, etc.