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X11 (X Window System)

  What Is X11 (X Window System)? X11, often called the X Window System, is a networking and display protocol that provides a basic framework for graphical user interface (GUI) environments. Developed by the Massachusetts Institute of Technology (MIT) in 1984, X11 is fundamental to UNIX and UNIX-like operating systems, including Linux, FreeBSD, and Solaris, though it can also be used with other operating systems. A Short Historical Overview of X11 X was conceived at MIT's Project Athena in 1984. The project aimed to create a robust, vendor-neutral, network-transparent window system. In 1987, X Version 11 (X11) was released, significantly enhancing its predecessors. X11 introduced a stable protocol that guaranteed backward compatibility in future releases, which was a key factor in its broader adoption. During the 1990s, the X Consortium was formed to manage the development of X. This non-profit was responsible for standardizing and promoting X. In the mid-90...
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Digital Down Conversion (DDC) Theory

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  The Digital Down Converter or DDC A fundamental part of many communications systems is Digital Down Conversion (DDC). Digital radio receivers often have fast ADC converters delivering vast amounts of data; but in many cases, the signal of interest represents a small proportion of that bandwidth. A DDC allows the rest of that data to be discarded, allowing more intensive processing to be performed on the signal of interest. As an example, consider a radio signal lying in the range 39-40MHz. The signal bandwidth is 1MHz. However, it is often digitised with a sampling rate over 100MHZ, representing in the region of 200Mbyte/second. The DDC allows us to select the 39-40MHz band, and to shift its frequency down to baseband. Once this is complete, the sampling rate can be reduced – with a 1MHz bandwidth, a sampling rate of 2.5MHz would be fine - giving a data rate of only 5Mbyte/second. This is shown in Figure 1. How It Works A DDC works by first shifting the bandwidth of interes...
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Simple VoIP setup in Ubuntu 22.04 using Asterisk

  TABLE OF CONTENT 1. Prerequisites 2. Configuration Steps 3. Create New Configuration Files 4. Restart and Reload Asterisk 5. Configure Zoiper 5 Clients 6. Test the Setup 7. Verify Setup 8. Conclusion   1.  Prerequisites 1. Ubuntu 22.04 installed and updated:         sudo apt update && sudo apt upgrade -y     2. Asterisk installed:         sudo apt install asterisk -y     3.  Zoiper 5 softphone installed on client systems.   4. All client devices must be in the `192.168.0.0/255.255.255.0` subnet. 2.  Configuration Steps   1. Backup Existing Asterisk Configuration Files Navigate to the Asterisk configuration directory and rename the default files: cd /etc/asterisk sudo mv sip.conf sip.conf.old sudo mv extensions.conf extensions.conf.old sudo mv voicemail.conf voicemail.conf.old   3.  Create New Configuration Files   Create ne...
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