Simple DiSEqC monitor and signal analyzer

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DiSEqC™ is a protocol developed by Eutelsat. It is widely used in satellite receiving equipment to control devices over the same coaxial cable that carries RF signal. DiSEqC can be used to select a local oscillator of the LNB, to operate a LNB switch or to point a motorized dish.

But when a device communication fault arises, the source of the problem may be difficult to find. The coaxial cable that goes from receiver to accessories and finally to LNB carries multiple signals: the radio frequency signal from LNB to receiver, the power voltage from receiver to connected devices and LNB and the DiSEqC signal. Faults can be caused by receiver, cable, accessories (switch, positioner, motor) or LNB.

The simple computer adapter that will be described allows you to view and analyze DiSEqC waveform using the soundcard input and Audacity software. This is possible because the protocol is modulated over a 22 kHz carrier. The same carrier (when sent continuously, at a smaller amplitude) tells the LNB to switch on the high local oscillator.

Simple DiSEqC monitor and signal analyzer

6 PDF page cropping tools for Linux

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If you ever needed to crop pages of a PDF document and you are using a Linux computer here are six tools that can help you. All are native Linux applications, some are opensource, but most important all are free.

I looked for the following features at these applications: the ability to select only a subset of pages from the document to crop, different crop boxes for each page and the way of selecting crop box (automatically, WYSIWYG or by measurement units).

Here are the six Linux applications that will help you when you need to crop a PDF. This is just a list, not a ranking.

6 PDF page cropping tools for Linux