It would be far more suceptable to interference than the AM equivalent.

Including heterodynes?

Theoretically, with optimal decoding, you require around 3dB C:N to decode
an AM digital signal.

3dB C:N as opposed to the 20dB C:N that you need to get a good AM signal
sounds to be a winner.

But AM would be about 30khz bandwidth, and this PCM signal would be 3mhz.

That means that the bandwidth gives you at least 20dB less sensitivity, so
comparing the signal bandwidth-wise, you only require 0dB C:N across the
same bandwidth to get the AM signal.

So you have a 3dB advantage for conventional AM over PCM.

Next, let us look at the nature of AM and heterodynes.

By the nature of audio AM, you will find that a single heterodyne can
degrade the C:N to as low as 10dB before it becomes perceptible.

So therefore in the same bandwidth with PCM, you then have -10dB C:N, which
is not enough to decode the PCM.

Therefore, PCM is inferior to AM, and you would not only be wasting precious
bandwidth, and face considerable issues with other transmissions and the
physical design of the antenna, transmitters and receivers, you would also
find that it is nowhere near as effective.

Maybe studying something like GSM compression or MP3 compression formats,
FEC and COFDM or similar may be your answer.

COFDM with a good FEC system is one of the most robust methods to transfer
digital data in the presence of heterodynes there is. With the correct
encoding and decoding techniques, you can have easily -80dB C:N because of a
heterodyne some 80dB stronger than your signal, and the data would be still
decoded correctly. Theoretically you could have hetrodynes thousands of dB
stronger than the carrier, but unfortunately the reciever technologies are
nowhere near that advanced yet, but even with cheap decoders, you could aim
for around 80dB as a realistic goal under ideal situations (which is what
you appear to advocate).


Sam
M1FJB