What is a SDR?

Software Defined Radio.

From wp2ahg:
Software Defined Radios (SDRs) are radios in which many of the functions of a transceiver are implemented in software rather than hardware.

The software may be embedded in the radio itself, or may be implemented in a personal computer connected to the transceiver.

For more info, please see Wikipedia's article Software-defined radio

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What does the DSP not do in a modern DSP radio?

Control SWR.

From wp2ahg:

A digital signal processing radio can control the frequency, modulation and detection, but has no control over SWR.

SWR (Standing Wave Ratio) is found in the feed line and antenna system, not in the radio.

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For more info illustrating the role of SWR, please see Wireless Communication site for the article on Software Radios

For info on SWR, please see Wikipedia's article on SWR Standing wave ratio and the article on Software-defined radio

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Which statement best describes the code used for GMDSS-DSC transmissions?

A 10 bit error correcting code starting with bits of data followed by a 3 bit error correcting code.

For more info, please see ITU site, for pdf of ITU-R M.493-10 DIGITAL SELECTIVE-CALLING SYSTEM FOR USE IN THE MARITIME MOBILE SERVICE, especially page 2 and the table on page 3.

For info on GMDSS, please see FCC site article Global Maritime Distress and Safety System (GMDSS)

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Which is the code used for SITOR-A and -B transmissions?

Each character consists of 7 bits with 4 “zeros” and 3 “ones”.

Best just to memorize 7 4 3.

For more info, please see Wikipedia's article on SITOR.

For very extensive details, see pdf from Apps Dtic Mil site on Report No. CG-D17-86 Coast Guard High Frequency SITOR and Digital Selective Calling Operational Review and Implementation Plan, Sept 1986, from US Dept of Transportation, US Coast Guard.

For reference source and more info, please see Crypto museum site for document Manual of Transmission Methods Reference Document. The answer is on page 324.

As this document is a comprehensive listing, it may be useful to download a copy for all transmission type info. To find info fast, use CTRL F, and search for the term.

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Which of the following statements is TRUE?

The Idle Signal (a) (0000111) is used for FEC Phasing Signal 1.

Best to just remember the Idle Signal (a) (0000111)

For reference source and more info, please see Crypto museum site for document Manual of Transmission Methods Reference Document. The answer is on page 324.

As this document is a comprehensive listing, it may be useful to download a copy for all transmission type info. To find info fast, use CTRL F, and search for the term.

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What principle allows multiple conversations to be able to share one radio channel on a GSM channel?

Time Division Multiplex.

That's when you use a single communication channel and you very quickly switch between parties, so each feels like they are the only ones using the channel.

For application in radio communication, please see Wikipedia's article on Time-division multiplexing

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