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TCP-group 1995


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Re: 56 kbit/s on 2 meters?



On Tue, 11 Apr 1995, Richard Chycoski Mail Drop wrote:

        I take this chance at lunch time to help clear the air about high
speed packet radio. First, let me say that attacks on no-code hams in the
tcp-digest is in the worst of taste! Most that I have made will never
read this. One has a PHD in Physics and can make most of us look like
kids. I dislike the Hams that are so stupid as to not understand what is
happening in Ham radio.

        Now back to FUN! I just read that FCC has given Hams the use of
219 to 220 MHz for high speed packet. So Roy Gould N5RG and I decided to
change our focus from rather high speed on 2 meters to Real High speed on
219 MHz. So we will design the first unit to be a complete radio on 219
MHz with crystal control.

        The bandwidth will be 100KHz and we will design for a packet
speed of 350,000 bits/second! This is a real fast system. It should be of
interest to commercial users.

        The modulator will be all cmos logic. The single sideband
generator will be of the phasing type. It is duck soup simple to get 90
degree phase shift of square waves from flip-flops. I will clock 2 Digital
to Analog converters (8 levels) from the phase shifted flip-flops. Data
will set the level of the output from the A-D units.

        The 2 A-D signals are mixed with a 10.7 MHz CW signal that is
also 90 degree phase shifted. The final mixer output is SSB at a carrier
frequency of 10.7 MHz. The phase shifts will be done to make a upper
sideband.

        The $2.50 filters at 10.7 MHz that are made for FM Radio work
fine for us. We will use a 103 KHz filter. As expected the receiver and
transmitter will use the same 10.7 MHz mixer to 219 MHz.

        The purpose is to make a cheap systtem that Hams can afford. For
this reason I select IF frequencies that have mass produced components.
The digital parts will cost less than $15 in single quantities.

        The first units will be made to work at 10.7 MHz where I can
measure bandwidth and data rate over a short path of 100's of feet. It's
clear that this system will need much tweeking.

        As for the usual no-code Ham and all the other Hams, almost, this
radio will be produced and sold to them. Plug and play.

73, karl k5di






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