The spectrum of this composite voice and video signal
FreeDV plus Video is a multi-carrier mode (see the diagram below)
This mode uses 66 sub-carriers, with 49 sub-carriers for video and 17 sub-carriers for digital voice (FreeDV "1600" mode -- note that the "700D" mode can also be used). The video is in YUV format, with 36 sub-carriers for the Y component (one sub-carrier for each line in the image), 4 sub-carriers for the U chroma component and 9 sub-carriers for the V chroma component. FM modulation on the video sub-carriers provides the Y, U and V information for the image. "Chrominance subsampling" permits the transmission of fewer chroma sub-carriers (see the "Technical" page for a link providing more information on chrominance subsampling).
In the diagram below, each of the 49 video sub-carriers is assigned a "B" number. This number corresponds to the "bin" in the filter bank (transmultiplexer) used to bandpass-filter that sub-carrier in the video RX software. See the "Technical" page for a link providing more information on transmultiplexers.
The FreeDV plus Video signal requires 3.5 kHz bandwidth for transmitting and receiving. Not all HF transceivers have sufficient bandwidth for this mode (see the "Hardware" page for a link to a list of suitable HF transceivers). Also, a crowded amateur radio band (like 20 meters on a contest weekend!) may not offer a clear spot 3.5 kHz wide.
In the U.S., FCC regulations permit a "multiplexed image and phone emission" to occupy the same bandwidth as a "communications quality A3E emission." A3E is double sideband, so the FCC rules allow 4-5 kHz bandwidth for FreeDV plus Video. See Part 97 of the FCC rules, para. 97.307(f)(2), p. 2 in the PDF link below.
Part 97 Link
- 5 July 2013 -
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