The “Bosun's Pipe - Navy-Marine Corps MARS

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MT-63Ref (A): FL BCST 10.08(B): FL NewslettersOn 30 July 2008, Ref (A) was promulgated stating that effective 15 August 2008MT-63 would become the primary mode for SCD traffic distribution on the FLNAVMARCORMARS nets. This BCST makes the process of connecting your stationcomputer through a sound card interface to your station transceiver for copyingand sending SCD traffic in this mode a priority for all members.MT-63 Technical DescriptionMT63 is intended for conversational use between one of more Amateur Radiostations, providing good performance under poor conditions, and consequently utilizesFEC rather than ARQ error correction processes. The MT63 modem, constructedaround a high speed DSP processor, either in a dedicated external DSP unitlike the Motorola EVM, or in PC software using the PC sound card, transmits 64tones spaced 15.625 Hz apart, in the 1 kHz bandwidth. The base-band signal occupiesfrom 500 Hz to 1500 Hz. All 64 tones are differential bipolar phase shift keyedat 10 baud. Since the Walsh FEC code is 64 bit, the character rate is the same as thesymbol rate, so the throughput with FEC is ten 7-bit ASCII characters/sec (about100 WPM). The following diagram (courtesy of Eduardo EA2BAJ) illustrates the 1kHz wide MT63 spectrum:MT63 Power SpectrumThere are two other bandwidths that can be used, 500 Hz, and 2 kHz, where thetone spacing and baud rate are halved or doubled, and the throughput halves or doublesrespectively. Unless otherwise indicated, this description is of the default 1 kHzversion.In addition, an optional doubling of the interleave period improves the temporal
esistance (e.g. to burst noise) at the expense of increased time delay through the encoder andBandwidth Audio Range Symbol Rate Character Rate Interleave500 Hz 500—1000 Hz 5 baud 5 char/sec 6.4 o4 12.8 sec1000 Hz 500 – 1500 Hz 10 baud 10 char/sec 3.2 0r 6.4 sec2000 Hz 500 - 2500 Hz 20 baud 20 char/sec 1.6 or 3.2 secThe user data from keyboard or file, (the data code is 7-bit ASCII), is further encoded into 64bits using a Walsh/Hadamard function to provide a highly robust FEC technique with highredundancy. The Walsh function ensures that up to 16 of the 64 bits can be corrupted, yet decodingwill still produce an unambiguous result.The MT63 signal is spread both in the time domain (temporally) and the frequency domain(spectrally). To ensure that noise bursts and other time domain interference artifactshave minimal effect, each encoded character is spread over 32 sequential symbols (3.2 sec).To ensure that frequency domain effects, such as selective fading and carrier interference haveminimal effect, the character is also spread spectrally by using all the tones across the width ofthe transmission.Why use MT-63 on FL NETS?1. “Reliability, Accuracy, Speed” are the three bywords when handling traffic on MARSnets. The first two are not to be sacrificed in achieving the third. The forward error correctionof AMTOR-FEC or PACTOR-FEC are not as robust as the error correction found in the MT-63 application providing a greater probability for accuracy using the MT-63.2. MT-63 does not require an expensive TNC to assure both good reception and transmissionof long SCD messages. It makes use of the sound card technology already in your stationcomputer.3. There are three readily available software applications for the member to use at no costor a nominal cost to the member.4. More of the states in Region FOUR are using or are moving to this mode for generaltraffic distribution.What do you need to have to use MT-63?1. Computer w/sound card, computer speakers, computer microphone and transceiver arethe absolute minimum hardware for receiving and transmitting MT-63. The quality and easeof using MT-63 is enhanced by the addition of an interface placed between the computer andthe transceiver requiring available COM port(s) for keying and rig control. You will also needa software application selected from the three mentioned in the previous section.2. The selected software will have to be installed on your computer and configured foruse on the nets (Note: any one of the three may be used with the minimum setup or with anenhanced setup using a hardware interface}
Page 1 and 2: The “Bosun’s PipeFL NAVMARCORMA
Page 3 and 4: and control instructions coming fro
Page 5: (closely related to PCALE) which is
Page 9 and 10: several steps in the RX/TX process.
Page 11: 210 / 3.750 (band center) = 56 (unk

The “Bosun's Pipe - Navy-Marine Corps MARS

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