[NLRS] Bandwidth limits...

[Dr.Gerald Johnson]

Actually the current rules for HF and VHF digital modes to tend to set 
the limits on bandwidth. They state a "signaling" rate, not necessarily a 
character rate. It is possible to run faster than 300 baud data on HF, 
by running multiple levels, or multiple simultaneous binary signals. That's 
done by HAL and others.

I don't see a need for rapid signaling rates on HF, though the multiple 
tone techniques do work, often the phase instability of HF 
propagation turns signaling rates greater than 75 baud into noise 
cutting the data throughput to zero. Look at the effective data rates 
of 300 baud packet for an example of that. 45 baud RTTY clunks 
through while 300 baud retries and retries tor days.

Many could conclude the 222 band is unused and so ripe for 
expansion in digital modes. There's also a 218 band in some areas only 
for digital modes.

Read the FCC rules in detail, there are wide band digital modes 
approved for the microwave bands.

Setting emission modes purely by occupied bandwidth is a freedom 
and opens up the potential for horrendous interference between 
incomparable modes. Nearly always the rules say "maximum" 
bandwidth for a band segment allowing the narrower band modes 
equal access. CW is quite narrow, but destructive when setting on 
one of the tones of a binary higher speed mode, though good modem 
design (known for quality RTTY Terminal Units in the 60s but forgotten by 
computer types) allows copy with one tone completely covered in 
QRM or lost due to selective fading. (Survey of techniques is included 
in my dissertation circa 1976 or in the circuits of the ST-6 terminal unit).  
The best solution for these incompatibilities are band plans separating 
the modes, but those only work when gentlemen (and gentlewomen) 
agree to go along with the voluntary band plans.

73, Jerry, K0CQ
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.