Topband: The use of digital modes on 160 metres

[Tom W8JI]

> While there may be many that disagree with me I love digital modes on 160. 
> I primarily use JT65 and it has been one of the reasons that I have worked 
> Japan and New Zealand on TB. I use it primarily when my hearing 
> disabillity kicks in and my ears start ringing and I work CW the rest of 
> the time. I can tell you that my ears do not like CW close to the noise 
> floor. The frequencies and modes most used (so far as I have heard) are 
> 1.836 6 for WSPR, 1.838 for JT65 and also 1.838 for PSK31.


I'm not endorsing or objecting to the concept of digimodes on 160 meters, 
but whatever happened to the ARRL bandplan?

http://www.arrl.org/band-plan-1

Our region sets digital modes as 1800-1810.

1835 up though around 1840 is used by CW as a DX CW work when the band is 
busy. I often try to stay above 1835 on CW during European propagation times 
to stay out of other people's hair when the band is very good and crowded 
with stations.

The problem with digital modes, in my opinion, is they often are not 
generated and decoded properly. They are generally audio baseband signals 
converted up to RF by a normal cheap transceiver's SSB chain, and converted 
back down through the SSB receiver.

This means most digital modes are subject to all the hum, noise, carrier 
suppression, opposite sideband suppression, and limited dynamic range of any 
SSB system. The limited dynamic range, caused by dumping encoded baseband 
audio into a SSB audio input and decoding through a SSB audio output, is why 
digimode people have such an affliction about power amplifiers. The 
transmitter system has all the issues of any SSB system. To "cure" the 
problem of IMD or maladies like hum, noise, or harmonic distortion inherent 
in any SSB communications system, they simply mandate making the signal 
weaker, so the inherent problems are buried in band noise.

160, because band layout is different than other bands, is a particularly 
unwise place to stick digimodes between normal SSB operations and weak 
signal CW operations. Had digimode positioning been planned by experienced 
160 operators and people who understand SSB systems, instead of 160 novices 
or those unfamiliar with SSB system issues as they relate to dynamic range, 
digimodes would never have been placed in an existing  DX communications 
band area between 1835 and 1840.

The root of this problem is inexperienced people who just decided a 100Hz 
(or whatever) wide varying amplitude audio signal into a TX SSB port always 
comes out exactly 100 Hz wide without hum, noise, carrier, harmonic 
distortion, or other inherent SSB transmitter maladies. Worse of all, 
"planning" never considered the CW area of 160 is "upside down", and the CW 
weak signal working band for the last 40 years primarily was 1825-1835+.

>From a purely technical standpoint, use of 1835 to 1840 is one of the worse 
ideas ever. This puts SSB transmitters down to 1835 or less dial setting, 
right in what was a weak signal area, usually in the hands of people who 
don't have a clue how the baseband-to-RF modulation and demodulation systems 
work.

This is entirely different than 80 meters on up, where there is an 
incredibly wide buffer area for digimodes and weak signal work areas. On 
160, lack of technical planning and experience with the band has now placed 
splattering or harmonic distorted signals, or placed common wiring design 
issues where people insist on running unbalanced lines grounded at each end 
between computers and the transmitter, right against (and into) two 
traditionally weak signal areas.

Eventually this might evolve into a solution, but that might take years if 
it ever happens. What will happen if digimodes stay between 1835 and 1840 is 
the DX area near 1835 will get pushed downwards by headaches with less than 
paper-perfect SSB transmitters, and SSB DX will get pushed upward away from 
1840 or less as the lower voice channel edge.

What I stated above, which is factually accurate, is why so many people 
resent audio tone software experimenters deciding they could just wiggle 
right into what were existing weak signal CW and SSB areas.

Many times over the winter season, I hear harmonics of audio tones well off 
the baseband bandwidth. I have to decode the signal to see who the guy is, 
and then try to convince him he has an issue with what he thinks (because he 
read it someplace) is a 50 Hz wide signal.

The entire notion of using 1835 to 1840 without proper band use and 
technical limitation investigation was either dumb as a rock, or terribly 
inconsiderate. Anyone understanding how band usage already worked and how 
**real** SSB systems work never would have used a 5 kHz slot in an area 
already used by weak signal operators.

73 Tom