[CW] Digital and Analog

[Ken Brown]

> "Digital" is, by definition, a toggling between two states, 1 and 
> zero, with no in-between.

That is what I always thought. I used to work on a 2 GHz FM microwave 
system with Analog multiplexing. The RF carrier was constant amplitude, 
and at the receiver end as long as the signal strength was high enough 
for the discriminator to demodulate it the SSB Multiplex channels would 
be demodulated. The amplitude of the RF carrier did not play a part in 
the information encoding.

Then we got a 10 GHz "Digital" microwave system that used QAM to encode 
a digital stream onto the carrier. In the new digital system the 
information was contained in the Phase AND AMPLITUDE variations of the 
RF signal.

The same is true of many modem schemes. Both the amplitude and the phase 
are used to encode the digital data. Often many bits are encoded into a 
single amplitude and phase state, and the QPSK or QAM "constellation" 
consists of many more states than just two. The number of states in the 
constellation and the number of bits encoded in a single state can be 
adaptable depending on S/N ratio of the transmission path.

In the end it's all Ones and Zeros, so it's digital, but in between 
there can be a lot of "in between".

DE N6KB