Topband: Topband Digest, Vol 117, Issue 20

[Tom W8JI]

> Tom, "on point" ....... I am, almost exclusively, a CW and Digi op in that 
> order.  I will say, anecdotally, that I have not experienced any 
> interference caused by one or the other to the other on 160.  I admit that 
> I am not THE most active op on 160, but I am there a fair amount of time.

Every experience will be different because of geographical location, antenna 
and equipment, noise floor, and operating habits.

Proper frequency planning requires understanding potential problems and how 
to handle them, not pretending if everything works perfectly and appears OK 
at the moment, it will always be OK.

Again, a good thing to consider is Collins. They assumed running a clean 
audio tone into the audio of SSB transceivers and transmitters was a good 
way to generate CW, and a good system to release into the field.

They must have assumed carriers were always balanced, there was never 
harmonic distortion, and there was never hum or noise. They probably assumed 
equipment would always perform like new, and always be properly operated. 
They got bit pretty hard by that. The lesson from that should have been 
audio injection of tones produces a limited signal-to-distortion ratio and 
is subject to equipment and operator malfunction.

If It goes in the front of a SSB bandwidth system, it should be treated as 
SSB bandwidth for distortion products.

Yaesu, for a more recent example, generated an almost square rise and fall 
waveform CW signal and processed it through a SSB system as a CW signal. The 
filter BW used was a few kHz. If they didn't waveshape properly later in the 
system, they should have ran it through a CW filter.

There is also a problem with NDB harmonics on 160. This is another case of 
poorly engineered systems that depend on perfect linearity to prevent 
interference. For all who think low level modulation followed by linear 
stages is a good system to prevent spurious, we can find many examples where 
that assumption caused problems. I can hear some 5th and 7th harmonics from 
25-50 watt  NDB transmitters from over 1000 miles away, and getting them 
fixed is like telling a digimode guy he has an issue with spurious.

This isn't a new, or unheard of, engineering problem.  I would think Hams in 
particular would be more in tune with proper planning that considers less 
than perfect systems.


> Since most 160 band plans, like the DX window, seem to have gone by the 
> wayside, it would be incumbent upon us as those who love the band, to come 
> up with one that includes the newer modes.  The reason?  Better 
> utilization by those who have WAY LESS than optimal stations for 160.

The real concern I have is growth in popularity of multiple modes that all 
go into a SSB transmitter audio channel, and that are all dependent on 
virtually no distortion or noise to maintain modest quality.

An example I would use for this is PSK31, where many users almost lynch 
other users who run more than a barely discernable signal. While the blame 
is placed on amplifiers, the root problem is very limited dynamic range of 
the system. Because it is so difficult to keep distortion and spurious TX 
levels down, and because receivers often pass much more BW than the desired 
signal, they decided to make everyone stay somewhat close to noise floor.

Like a used car dealer would do, limited dynamic range is presented as a 
"feature". Saying "No one needs power or good antennas because the mode is 
so efficient" is a good way to mask issues caused by amplitude changes in an 
audio tone driving a SSB transmitter, and using a wide SSB channel in a 
receiver of a narrow band signal.

You won't find many CW operators who think 2.7 kHz IF filters followed by a 
31 Hz wide audio filter is a good system for dynamic range.

As audio into SSB transmitters and back through SSB receiver modes become 
more popular, it will be tougher to keep a *lid on shortfalls*. There also 
won't be a *shortfall of lids* (intended as a pun) who mis-adjust things, or 
wire things wrong.

Ask yourself this...

If digimodes get more and more popular, where will they expand if we start 
them smack in the middle of what was a weak signal area? Does anyone here 
really think the best place to have started digital modes was in the middle 
of the most popular DX weak signal area?

Or are we really just pretending 1835-40 was a good idea, and there will 
never be more than 30 operators using digital modes, all QRP, and all with 
perfectly adjusted radios?

73 Tom