Excerpt from an articled titled "Earth-shaking ATV, Plus.." by N5EM in CQ-VHF Magazine, March 1999
Digital ATV Is Heating Up!
Since I last wrote about some possibilities in Digital Ham TV (DHTV), several reports of experimentation have been received. As long as there are efforts to make digital ATV a reality , I'll report on the work and keep you informed. One of the best developments is the previously mentioned e-mail re-mailer for DHTV. Check out the Web address for information about reading and posting messages to this list.
For those of you who may not have yet experienced an e-mail list, it is the method of sharing information in the information age . By "subscribing" to the list, you become a recipient of any e-mail message that is sent to the list. Anytime a message is e-mailed to the list, it is re-mailed to every subscriber, all in a matter of minutes. It lets people share ideas and information on a near real-time basis with like-minded experimenters any where in the world.
There are e-mail re-mailers (also called "reflectors ") for virtually any subject the mind can conceive of. Some have only a handful of subscribers while others have literally hundreds of thousands . There are several good e-mail re-mailers for the ATV community. One place to find out about them is at the Houston Amateur Television Society's Web site located at <http://www.stevens.com/HATS/>.
Some work with DHTV this month comes from Les Rayburn , KT4OZ, and Tom Askew, KB5IHI. They've been experimenting with video transmission using IBM Wireless LAN PCMCIA cards operating on 2.4 GHz. In their tests, Les and Tom used two laptop computers and wireless LAN (local area network) cards, transmitting Real Media data streams approximately 800 feet and resulting in actual ATV QSOs. Quoting from their test report,
"At 28.8 kbps encoding, it was...possible to have two-way (full duplex) QSOs, but at 56 kbps encoding the stream broke often. The Wireless LAN cards have a rated bandwidth of 512kbps but much of this is taken up by the protocol functions .One-way QSOs were possible at virtually any encoding speed, and high quality video (P5) was exchanged out to our maximum distance."
Not bad for a couple of laptops and a pair of $30 LAN cards. These LAN cards use spread spec trum and are Part 15 devices (they don 't require a license when used without modification). Since Les and Tom plan to modify these cards with the addition of amplifiers and external antennas , they've decided to participate under the Special Temporary Authorization (STA) of the Tuscon Amateur Packet Radio organization (TAPR) that allows the use of the frequency- hopping method employed by the wireless LAN cards in the amateur band s. After having initial success using the Real Media streams, Les and Tom have transmitted MPEG1 streams at distances of up to three miles using the unmodified Part 15 devices. These streams have included pictures, callsigns, and voice in each test.
So, DHTV experimentation is alive and well in the U.S. Other amateurs are participating in the experimentation and discussion, including Clint Turner, KA7OEI, in Salt Lake City, Utah , and Woody Winstead , KJ4SO, in Raleigh, North Carolina. If this interests you, subscribe to the DHTV re-mailer and start learning about the future of ATV.
I don 't want to leave you with the impression that DHTV is something going on only in the U.S. Quite the contrary- digital ATV experimentation in Europe is several years ahead of us. As early as 1996, the Austrian ATV organization had proposed MPEG 1-based digital ATV as the new standard for the 70centimeter band. This was to try to reduce the constant pressure on spectrum-intensive modes like ATV in countries where the total 70-centimeter band is considerably smaller than what we enjoy in most of the U.S. If you would like to read this proposal, you can find it on the Internet at <http://www.amrad.org/DigitalTV.html >. It's a very enlightening concept.