[CW] Digital and Analog

[Ken Brown]

I have added a couple of details that help make the point.

> "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 transmitter PA operated in class C and the receiver 
IF had AGC and limiter. 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 transmitter PA was a linear amplifier and the receiver 
had AGC which had to have just the right time constants.

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