Sunday, November 20, 2011

70cm DATV and the future

Here is an interesting excerpt from an articled titled "Earth-shaking ATV, Plus.." by N5EM in CQ-VHF Magazine, March 1999 that I recently ran into.

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 .

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 . It's a very enlightening concept.

Ten years or so later, and we sadly aren't much further.

TAPR recently created a DigtalATV yahoo group. From what I gather DATV is pretty popular in Europe. The problem is it will cost nearly $2,000 to do 1 watt QAM Digital or DVB-S.

Not to practical for a one way transmitter in my book. It has been said that Image communications were never intended to be a mode independent of phone.

With that said, and the early experiments using less expensive 802.11 gear to achieve the same, I'd like to re-introduce that idea.

For those not up to speed, a normal 802.11 signal is 20 MHz wide. This is not a problem on 900 MHz or above, since there is plenty of space and little crowding.

For those not aware, if you use Atheros chip based 802.11 gear, half rate (10 MHz wide), and quarter rate (5 MHz wide) options are available using open source drivers.

And even more interesting is that that within the Atheros chip it is possible for licensed developers to enable a local oscillator generation for a direct conversion radio transceiver. This is not an open function, but irregardless, this is how 802.11 products on 900 MHz (Ubiquiti XR9), and 3 GHz (XR3).

And now 420-450 MHz with a module designed by Doodle Labs.

This is perfect for this type of application, as well as a multitude of other amateur infrastructure applications.

You can read more on the history of ATV and HSMM here:

And what other hams are doing with (muti-mode) 802.11 here:


James said...

Your post reminded me of another blog post I've read lately:
W0FMS talks of a board called the digilite.
It seems to be a hardware device that can be built to transmit a low bitrate DVB-S of 1 or 2mbit. I guess it's heavily computer bound, you need a Windows machine and a Hauppauge tv tuner card with the hardware mpeg-2 encoder.

While searching for that, I found these links to other resources:

Never really thought about using video sending programs over wifi as DATV. I guess that could be a use for HSMM networks that doesn't just make them a watered down Internet. (which, sadly, seems to be the impression to a fair number of people who would dismiss the idea.)

I'd like to see a radio much like the mobiles and HTs that worked over wifi as well. That'd be another interesting application. Can't get on the repeater on 2m? If there's a HSMM node near you, switch to wifi. It'd probably take a lot of work to build something like that though. I have seen homemade internet radios that connect over wifi before.

Kyle said...

I was thinking about picking up a pair of doodle labs 70cm units to play with but then I remembered that for data modes on 70cm you are only allowed to use 100khz and nothing faster than 56kbit? am I remembering this right?


Kyle said...

Well, I just ordered two of the 70cm units. As long as I transmit video it should be legal. I'll do a write up of my tests. Perhaps that would get others interested in this as well.


Dan MD1CLV said...


I just wanted to say I've only just discovered your blog and it's great to see other people interested in pushing the hobby forward!