56 kbit/s on 2 meters?
- To: TCP-Group@ucsd.edu
- Subject: 56 kbit/s on 2 meters?
- From: Klarsen <firstname.lastname@example.org>
- Date: Sat, 8 Apr 1995 07:11:53 -0600 (MDT)
Hello Ham Packet Radio users. I was today shown what in 17
years will be "standard television". It is very high definition
television pictures with 4 audio channels so you can have the best
possible sound. These television stations will send all this stuff
to our home using radio frequencies and from mountain tops send
the signal to millions of receivers.
The real shocking thing is that the "new" method of getting
all this data to the tv viewer has been in common use by Hams for
many years! We just didn't do it all together towards the same
goal. The new television standard is still a 6 MHZ channel like
right now, but the transmission method will be the same old one
used now for the video signal, which is single sideband suppressed
carrier, and do away with the current FM audio channel. The single
sideband suppressed carrier (ssb) in the new system will use the
entire 6 MHz bandwidth and will have a "pilot carrier" that allows
the receiver to add the "carrier" back in with accuracy.
And the picture and sound is pure digital! They are both sent
to the receivers as digital information. And guess what? All this
data is sent in PACKETS. Each packet has 8 bytes of "information"
and the rest of the packet, about 200 bytes, sound familiar? is
data. The packets are sent fast to your TV.
To increase the data transfer the digital data will have 8
amplitude levels. In this way, much like our high speed telephone
modems, we get 4 times the data transfer you get if every pulse
has the same amplitude.
So what does this have to do with Ham Radio? Well it should
cause us to look at what we now do and consider changing to a
packet transmission method that is receiving millions of dollars
of research as I write this. I think we should look at Amplitude
Modulation again. We should look at Trellis methods of increasing
bit rate over baud.
This means new radios. Off with the old HT or Motorola Police
radios that we use now. The new radios, say for 2 meters will be a
digital low band transmitter on say 30 MHz. This then is moved to
145.01 MHz with a "transverter" that is linear and after this is
the "linear amplifier" to say 10 watts. The reciever will have a
simple AM type of demodulator and then some digital processing and
the received digital data comes out directly to your computer! No
more "TNC" types of equipment.
How fast can we go? Well on 2 meters we can have 20 KHz of
bandwidth and, if we use the new TV system we should get about
56,000 bits/second in that bandwidth! As you know, we now creep
along at 1200 baud in that same channel.
Do not think that the current packet systems, based on a
1970's telephone modem and old FM radios is going to be the end of
Amateur Radio Packet. It HAS been for 10 years now but thhe time is
NOW to design a new radio and make small changes to the AX.25
protocal. Believe it or not, the new TV system uses packets not at
all different from AX.25 protocal.
I wish to thank co-workers at the Army Research Laboratory
who are members of IEEE and bring to my attention what's going on
in the world. It is exciting.
73, de karl k5di