Created Plugins for special devices (markdown)

Plugins-for-special-devices.md

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+These plugins do not use any hardware device connected to your system.
+
+<h2>File input</h2>
+
+The [File input plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/samplesource/fileinput) allows the playback of a recorded IQ file. Such a file is obtained using the recording feature. Click on the record button on the left of the main frequency dial to toggle recording. The file has a fixed name `test_<n>.sdriq` created in the current directory where `<n>` is the device tab index.
+
+Note that this plugin does not require any of the hardware support libraries nor the libusb library. It is always available in the list of devices as `FileInput[0]` even if no physical device is connected.
+
+The `.sdriq` format produced are the 2x2 bytes I/Q samples with a header containing the center frequency of the baseband, the sample rate and the timestamp of the recording start. Note that this header length is a multiple of the sample size so the file can be read with a simple 2x2 bytes I/Q reader such as a GNU Radio file source block. It will just produce a short glitch at the beginning corresponding to the header data.
+
+<h2>File output</h2>
+
+The [File sink plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/samplesink/filesink) allows the recording of the I/Q baseband signal produced by a transmission chain to a file in the `.sdriq` format thus readable by the file source plugin described just above.
+
+Note that this plugin does not require any of the hardware support libraries nor the libusb library. It is always available in the list of devices as `FileSink[0]` even if no physical device is connected.
+
+<h2>KiwiSDR</h2>
+
+The [KiwiSDR plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/samplesource/kiwisdr) is designed to enable connection to publicly available [KiwiSDR](http://kiwisdr.com/) receivers.
+
+<h2>Test source</h2>
+
+The [Test source plugin](https://github.com/f4exb/sdrangel/tree/master/plugins/samplesource/testsource) is an internal continuous wave generator that can be used to carry out test of software internals.
+
+<h2>Remote input</h2>
+
+Linux only.
+
+The [Remote input plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/samplesource/remoteinput) is the client side of an instance of SDRangel running the Remote Sink channel plugin. On the "Data" line you must specify the local address and UDP port to which the remote server connects and samples will flow into the SDRangel application (default is `127.0.0.1`port `9090`). It uses the meta data to retrieve the sample flow characteristics such as sample rate and receiving center frequency. The remote is entirely controlled by the REST API. On the "API" line you can specify the address and port at which the remote REST API listens. However it is used just to display basic information about the remote.
+
+The data blocks transmitted via UDP are protected against loss with a Cauchy MDS block erasure codec. This makes the transmission more robust in particular with WiFi links.
+
+There is an automated skew rate compensation in place. During rate readjustment streaming can be suspended or signal glitches can occur for about one second.
+
+This plugin will be built only if the [CM256cc library](https://github.com/f4exb/cm256cc) is installed in your system.
+
+Note that this plugin does not require any of the hardware support libraries nor the libusb library. It is always available in the list of devices as `RemoteInput` even if no physical device is connected.
+
+<h2>Remote output</h2>
+
+Linux only.
+
+The [Remote output plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/samplesink/remoteoutput) is the client side of and instance of SDRangel running the Remote Source channel plugin. On the "Data" line you must specify the distant address and UDP port to which the plugin connects and samples from the SDRangel application will flow into the transmitter server (default is `127.0.0.1`port `9090`). The remote is entirely controlled by the REST API. On the "API" line you can specify the address and port at which the remote REST API listens. The API is pinged regularly to retrieve the status of the data blocks queue and allow rate control to stabilize the queue length. Therefore it is important to connect to the API properly (The status line must return "API OK" and the API label should be lit in green).
+
+The data blocks sent via UDP are protected against loss with a Cauchy MDS block erasure codec. This makes the transmission more robust in particular with WiFi links.
+
+This plugin will be built only if the [CM256cc library](https://github.com/f4exb/cm256cc) IS installed in your system.
+
+Note that this plugin does not require any of the hardware support libraries nor the libusb library. It is always available in the list of devices as `RemoteOutput` even if no physical device is connected.
+
+<h2>Local input</h2>
+
+The [Local input plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/samplesource/localinput) is similar to the Remote input discussed above but is the output of an internal pipe of samples instead of the local end of a remote sender over the network. It receives its samples flow from a [Local sink channel plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/channelrx/localsink) present in another source device set.
+
+It can be used to use a narrow part of a receiver pass band to use it at a lower sample rate and thus "see" it in more detail.
+
+<h2>Local output</h2>
+
+The [Local output plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/samplesink/localoutput) is similar to the Remote output discussed above but is the input of an internal pipe of samples instead of sending samples over the network to a distant SDRangel remote source. It sends its samples flow to a [Local source channel plugin](https://github.com/f4exb/sdrangel/tree/dev/plugins/channeltx/localsource) present in another source device set.
+
+It can be used to build a complex narrowband signal with multiple modulators and send it as part of a broader band transmission.