Amateur Television (ATV) today operates in basically 3 modes:

• Slow-Scan TV signals sent, mostly, over HF bands for transmitting still, analog images over large distances. I believe that Kenwood’s new VC-1 handheld camera is an integrated SSTV system for use with handheld transceivers.
• Fast-Scan TV signals requiring large bandwidth (6 to 9 MHz) and transmitted at UHF only.
• Still digital images (JPEG files) transmitted over packet radio networks.

A number of Amateurs have begun experimenting with digital "fast scan" or "broad bandwidth" TV. That is to say, high quality television using digital compression and modulation techniques, and especially geared to broadcast functions. Most amateur experimenters have had access to expensive commercial equipment needed (at this point) to perform broad bandwidth digital TV. Broad bandwidth Digital TV uses MPEG video compression encoders to convert video data streams into a format that can be used for transmission over the air. Even after compression, most digital video schemes require over 1 million bits per second data rates for "VHS quality" video. While this is certainly with in range of skilled Amateurs for the purposes of experimentation, this type of technology, particularly regarding cost, is going to outside the scope of most Amateur budgets for some time to come.

Many commercial entities are producing "digital TV" systems using the Digital Video Broadcast standard or DVB. In these types of schemes, multiple video channels are digitized, compressed and statistically multiplexed together into a single 38 Mbps data stream. This 38 Mbps data stream is modulated into a 6 or 8 MHz carrier bandwidth. Typically 6 to 10 video signals are transmitted simultaneously in one of these video channels. The cost and complexity of this level of performance will remain outside the scope of individual Amateurs for a long time to come.

A second approach to digital imaging is to use digital technology and data networking for image transmission but not necessarily, at least for now, going after "broadcast" quality. My comments on "Amateur Digital Video" focus on this category of routing pictures, and especially motion pictures, over data networks. This category of "Amateur Digital TV" or what I call Amateur Digital Video (ADV) is a place where Amateurs can offer significant contributions to the state-of-the-art by creating simple, low cost solutions that can be widely deployed. Existing low cost off-the-shelf solutions make all this possible.

How do we do this? The answer is to leverage the technologies of the Internet. Many products have been developed by computer companies to deliver digital imaging over the Internet. These technologies are designed to scale to the available bandwidth so that they can work on a telephone modem, an ISDN line or a fast Internet connection. Best of all, they are available now, off-the-shelf. Amateurs do not have to re-invent or invent new solutions for the Amateur radio world but can leverage existing technologies. And these existing solutions have the benefit of leveraging the Internet itself – ADV linking is automatically available through the Internet. Pictures from a disaster scene can be linked live to a web site used by emergency managers, for example.

The huge advantage of leveraging Internet video technologies is that anyone who has a personal computer – or a notebook computer – or even a handheld PC – or a WebTV-like Internet-to-TV interface – is well along to receiving "Amateur Digital Video". I’ve used QuickTime 3.0 and RealPlayer on the Macintosh – and Windows Media Player and RealPlayer on Windows – both platforms provide numerous tools for decoding video streams. Further, there are many products available for encoding video streams to match the available bandwidth. In this way, ADV can use off-the-shelf technology to generate low cost digital data streams that are optimized for use over what ever Amateur data technologies are available – ranging from 9600 bps to 56 kbps modems, and up to 1+ Mbps data networks.

The key concept is that leveraging Internet technologies enables the widespread deployment of low cost ADV that scales to the resources of Amateurs. ADV reception becomes very low cost as most Amateurs already have most of the basic technology on their personal computers. Portable reception is possible using existing handheld computer devices that support the Internet. Amateurs sometimes build exotic one-of-kind solutions that, due to low volumes, end up being made of unobtanium. The high volumes of Internet technology ensure a plentiful supply of low cost components.

Additionally, by using Internet technologies, it becomes possible to link ADV repeaters together using the Internet itself. ADV signals can be cross-linked from the Amateur radio bands, into the Internet, and relayed again out over ADV links at destination sites. In some applications, such as at emergencies and disasters, emergency managers can view incoming video feeds routed directly to a web site. Amateurs will undoubtedly invent many new applications of ADV technology, used stand alone or in conjunction with the Internet. Today, voice repeaters are linked across the Internet – imagine a digital TV link between an ATV repeater in Seattle and an ATV repeater in the San Francisco bay area – this is now possible.

video repeaters and those who would build high speed digital repeaters. I

think the mindset is there for the "data" folks" but the video folks have not yet seen the digital opportunity.

According to N8GNJ, "We now have an end point of the Vancouver 56K repeater network operating at Camano Island. We have the designer/builder of the 56K repeaters and transverters, and now a 56K modem living in Redmond. The 56K gear that he designed was with the intent to grow it to 2 Mbps relatively easily. That's a speed that's interesting enough to start re-attracting "Internet techies" into Amateur Radio for the price of getting a Tech Plus ticket."

Initially, ADV will likely work on a mix of technologies ranging from Amateur 56 kbps gear to modified Part 15 equipment in the 902-928 MHz and 2.4 to 2.45 MHz Amateur bands. As the radio technologies advance (and come down in cost), higher bit rates become possible and higher quality digital video becomes common place. But using off-the-shelf equipment, KT4OZ and KB5IHI have produced a short range, low powered ADV station for just $300.

Purest will argue, correctly, that there are significant problems in the use of TCP/IP for broadcast functionality. However, many academic and corporate researchers are working on solutions to fixing the problems in IP networks to better accommodate multi-cast and time-bounded transmissions. There are hundreds of millions of TCP/IP users – including not only Internet surfers but corporate networks and many kinds of devices that connect directly to TCP/IP networks. Many people are making enormous investment in TCP/IP technologies – these technologies are not going to go away but will be improved to meet customer requirements.

Amateurs can leverage the investment that so many others have made in Internet technologies and can create innovative, low cost, flexible, scaleable, widely deployable, Internet linkable Amateur Digital Video.

With ADSL and cable modem technology not rolling out, the concept of linking ADV and existing ATV repeaters together over the Internet is a reality. As N8GNJ notes, "I expect someone to come out with a single board PC

that runs, perhaps Linux, perhaps Windows CE, and does H.323 (an Internet standard for video conferencing) and has an input for a USB QuickCam and connects to the family's big screen TV, and boom, you start doing videoconferencing."

reprinted with permission from ham radio online