FDMDV A New Digital Voice Mode for HF Marc C. Tarplee, Ph.D. N4UFP SC Section Technical Coordinator.
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Transcript of FDMDV A New Digital Voice Mode for HF Marc C. Tarplee, Ph.D. N4UFP SC Section Technical Coordinator.
![Page 1: FDMDV A New Digital Voice Mode for HF Marc C. Tarplee, Ph.D. N4UFP SC Section Technical Coordinator.](https://reader030.fdocuments.us/reader030/viewer/2022032709/56649ebc5503460f94bc47e3/html5/thumbnails/1.jpg)
FDMDV
A New Digital Voice Mode for HF Marc C. Tarplee, Ph.D. N4UFP
SC Section Technical Coordinator
![Page 2: FDMDV A New Digital Voice Mode for HF Marc C. Tarplee, Ph.D. N4UFP SC Section Technical Coordinator.](https://reader030.fdocuments.us/reader030/viewer/2022032709/56649ebc5503460f94bc47e3/html5/thumbnails/2.jpg)
What is FDMDV?
• FDMDV is a new digital voice mode developed by Peter Martinez, G3PLX, and HB9TLX
• Advantages of FDMDV – Narrower bandwidth than SSB (1.1 KHz)– Should provide good copy at SNR of 3 dB
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How does FDMDV work?
• Voice data is sent over 15 carriers– 75 Hz carrier separation gives 1125 Hz BW
– 50 baud QPSK is used on 14 carriers for an overall data rate of 1400 bit/sec
– Center carrier is used for synchronization
• There is no Forward Error Correction (FEC)• Analog voice signals are not directly converted to a digital
signal, but are encoded by a vocoder
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Vocoders
• A vocoder is a device that – Creates a mathematical approximation to a human voice and
outputs the key parameters of that approximation as data
– Creates voice sounds based on its internal mathematical model and numerical data that it receives
• Vocoding is not simple A/D conversion– The output is not digitized signal amplitude
– The sampling rate does not have to be twice the highest audio frequency present
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Vocoder Model
• Broadband “buzzing” sound source (vocal cords)• Tube with multiple resonances (formants)• Additional “basis sounds”
– Plosives (puffs of air – b, d, p sounds)
– Fricatives
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Vocoder Operation
• Vocoder analyzes the incoming voice signal to determine:– Number of formants– Quality of formants– Amplitude of basis sounds
• Numerical parameters describing the items above are the data output
• Data output rate is much less than the Nyquist sampling rate required by traditional A/D conversion
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Vocoder Limitations • The choice of basis sounds in somewhat language-
dependent.– FDMDV vocoder is optimized for Germanic languages
(English, German, Dutch, etc.)– The received quality of non-Germanic languages is poorer
• The vocoder must fit incoming audio to its internal human voice model– Non-voice sounds such as music are not faithfully reproduced
![Page 8: FDMDV A New Digital Voice Mode for HF Marc C. Tarplee, Ph.D. N4UFP SC Section Technical Coordinator.](https://reader030.fdocuments.us/reader030/viewer/2022032709/56649ebc5503460f94bc47e3/html5/thumbnails/8.jpg)
FDMDV Signal
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FDMDV Station Requirements• Amateur transceiver that has low frequency drift
– Any modern solid state rig is OK (IC-706, IC-746, TS-940, TS2000, FT-1000, Omni VI, etc.)
– Vacuum tube rigs can be problematic, unless ample warm-up time is allowed (15 – 30 minutes)
• PC and Soundcards – Operating System - Windows 98, ME, 2000, XP– Sound Card(s)
• 1 Sound card with USB mic/headset or 2 Sound cards• Sound cards should be able to sample at 12Khz rate
• An interface that connects the PC and the transceiver• Software
– FDMDV– MELP1400.dll
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Audio Interface Circuits
1. Acoustic Coupling (Tayloe Interface)
– Rig’s speaker is placed near the PC’s microphone
– Rig’s microphone is placed next to the PC’s speaker
– VOX is used for T/R switching
– Advantages• Absolutely no extra equipment required.
• Good electrical isolation between PC and rig
– Disadvantages• Transmit levels can be tricky to adjust
• Ambient noise degrades signal
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Where to hear FDMDV
• FDMDV activity is concentrated around 14.236 MHz
• There are regular nets that begin at 2000Z on Saturday and Sunday afternoons on 14.236 MHz
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Tuning in a PSK-31 signal• Turn on the
equipment• Run the PSK
software• Select the waterfall
display mode• Use the mouse to
place the cursor on a signal
• Adjust the squelch until text appears in receive window
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Where to Find More Information
•www.arrl.org (members only, search for PSK31)
•www.ssiserver.com\info\psk31 (copy of thispresentation as an Adobe PDF document)
•www.psk31.com (“official home page”)
•www.aintel.bi.ehu.es/psk31.html (“official home page”)
•www.arrl.org/tis/info/HTML/psk31 (Steve Ford’s original QST article)
•Email reflector: send email to [email protected]. Put “subscribe” in the subject line.
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Where to Find Software and Information
• Hamscope may be downloaded from the following website– http://www.qsl.net/hamscope/
• W1SQLPSK may be downloaded from the following website:– http://www.faria.net/w1sql/
• Digipan may be downloaded from the following website:– http://mywebpages.comcast.net/hteller/digipan/
• “PSK31 Official Homepage”an excellent source for background information
– http://aintel.bi.ehu.es/psk31.html
• Good reference material and links– http://www.arrl.org/tis/info/psk31.html