Bill,
> For a signal to be "digital", the data has to represent numbers. That
> is what the word "digital" means. In the case of RTTY, the bits are
> purely analog signals, which is why they can be decoded with an analog
> computer, namely a teletype machine. There is no number crunching
> involved. You can, of course, digitize the signal just as with any
> analog signal and process it, but the original signal was and is
> analog.
I don't know if you are being dense or just being intentionally difficult.
For a mode (specifically a "mode of emission") to be digital it is only
necessary for the signal to take a limited (finite) number of distinct
states as opposed to an infinite number of states between a set of
limits (amplitude, frequency etc.).
Putting that aside, CW, RTTY, PSK31, etc. are still all digital by
your definition of digital. RTTY is a five bit code of 32 "numbers"
- each of those numbers is assigned a value, some even more than one
value based on the shift state. Although it was not first
conceived as such, CW is a variable length code (also known as
varicode). Each character is actually a numeric value starting
at zero (three "space" bits) representing the letter space and
getting progressively longer/larger through the prosigns.
> If CW is digital, it then follows that dit-dah and dit-dit have
> the same numeric value and are therefore the same character.
Here is where you are demonstrably wrong again ... dit-dit is
the varicode 101 (5 decimal) while dit-dah is 10111 (23 decimal).
This is the nature of a variable length code.
> CW and RTTY both have "bits" of different lengths, and that is
> crucial to their decoding. Both are analog signals which *can*
> be processed digitally, but the original signal is analog.
Dead wrong! It does not matter what the original data is - it
is only the MODE OF EMISSION or the "coding" that matters. Any
signal can be transmitted using digital modes of emission.
73,
... Joe, W4TV
_______________________________________________
RTTY mailing list
RTTY@contesting.com
http://lists.contesting.com/mailman/listinfo/rtty
|