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Carter Ward
Carter Ward

WiFi Radar Pro 3.4.1 EXCLUSIVE



Have you ever wondered why certain channels in the 5 GHz band, more specifically in the 5.25-5.35 GHz (UNII-2) and 5.47-5.725 GHz (UNII-2e) frequency bands are (almost) never in use by Wi-Fi devices? Well, it happens that, worldwide, these unlicensed frequency bands are also used by radar systems. So, for a Wi-fi device to operate in one of these bands, it must support Dynamic Frequency Selection (DFS). DFS is a mechanism (not limited to Wi-Fi) that allows a device to dynamically select or change the operating frequency to avoid interfering with other systems. In other words, regulatory bodies require Wi-Fi devices to use DFS to make sure devices will not interfere with your local weather radar system, for example.




WiFi Radar Pro 3.4.1



In the context of Wi-Fi, an access point (AP) that supports DFS must be able to detect radar signals during the channel start-up and in-service phases. If radar signals are detected, the AP will stop transmitting and then select a new channel. Once the new channel is selected, the AP informs nearby clients to clear the channel and move to a different frequency by including the Channel Switch Announcement IE in the beacon frame. DFS-compatible Wi-Fi clients, on the other hand, cannot start transmitting until authorized by the AP and cannot perform active scanning (i.e. transmit probe requests) until Wi-Fi activity from nearby APs is detected. They also must be able to clear a channel when commanded by the AP.


We can illustrate how DFS works with Wi-Fi devices by emulating radar signals using a HackRF and GNU Radio. A HackRF is a Software Defined Radio (SDR) peripheral capable of transmission or reception of radio signals from 1 MHz to 6 GHz. Why a HackRF? Because I got one during the last #WLPC and I thought I could give it some use after stumbling upon this blog post by Bastian Bloessl, where he uses GNU Radio and a USRP to emulate radar signals.


First, we need to know how radar signals look like so we can emulate them. Each country and regulatory domain defines its own DFS requirements and test radar signatures. These test waveforms are developed based on the technical characteristics of existing and future radar systems operating in the 5 GHz frequency range. In the case of the US, the FCC (Part 15 Subpart E Rules) defines 5 different short pulse radar test waveforms, 1 long pulse radar test waveform, and 1 frequency hopping radar test waveform.


Second, we need to build a GNU Radio flow graph to generate the radar signal pattern over a given DFS frequency. In this example, we will use a type 4 pattern with a pulse width of 15 µs and a pulse repetition interval of 250 µs. The radar signal pattern looks like this:


21 July 2005 Updates from the helmA couple of things have happened since the last update.First, another alpha version of the next major release of Meteo, Meteo 2.0a2, was released on June 5th. See the release notes and give it a try - but only if you're feeling adventurous - the version is still littered with numerous bugs.In addition, it appears that weather.com recently broke the search function for many European cities. The Meteo team will look into this soon to try to resolve the issue.Lastly, the FAQ has just been updated to include a question about adding radar to your list of weather items. Note that while radar it turned off by default, you can still add it! Just go over to the FAQ and see for yourself. [ Discuss... ] 041b061a72


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