Topband: Topband Digest, Vol 117, Issue 20

[Mike Armstrong]

Tom, 
I never said putting digimodes in the middle of the weak signal area was a good idea, but I also know that the weak signal area is violated constantly by local station using it.  By that I mean US stations talking to US stations there.  To me, personally, I considered 160 DX to mean outside your own continent.  So if we call CQ there, we should answer replies from outside our own continent only...... In fact, I shouldn't answer any cq that is in my country or continent in that segment.  Obviously, this would have to be modified for some continents like europe..... But then again maybe not because "close is close" and "loud is loud."  

I don't know..... Maybe I don't have a clue what I am talking about...... When it comes to areas of spectrum reserved for weak signals.... Because it is very hard to define what that means and how to properly regulate when/who should be in it and for what reasons.  I never said the answer would be easy, either.

But one anecdotal piece of evidence concerning bad signals or distortion products or anything else of that nature as part of this discussion.  Most of us who are serious about digi have very narrow filters in line with our IF.  Example: the ONLY time I ever have a normal SSB filer in line (eg, anything with a BW greater than 1800 hz) is when I am "monitoring" for signals in an apparently dead band.  Any other time, I am using 300 hz or less.  Normally it is 300 or 200 hz.  In that narrow bandwidth I have regularly had cases where I could detect 3 to 5 other conversations going on at the same time....... And not disturbing me in the slightest as long as they weren't pumping my AGC due to overwhelming signal strength or.... ON VERY RARE OCCASION..... Someone is putting out a crummy signal.

Tom, all you have to do is open you filter up to say 1800 hz or maybe a little more, then sit and watch how many  signals you can decode on a busy 20 meter psk31 day.  I regularly copy signals that are almost in the noise while surrounded by louder signals only 20 or 30 hz away..... 20 or 30, NOT 200 or 300 hz away.  I kid you not..... Well, if the signals were as lousy as you seem to think most of them are, you wouldn't be able to do that with any regularity..... I have it happen almost every weekend and even during weekdays on 20 and 15 meters.  In fact, given the number of hams who call 20 meter digi "home," it is the NORM, not the exception.

I understand what you saying about Collins and the entire concept.  BUT, the truth of the matter, experientially, is that we MUST be producing mostly clean signals or you wouldn't be able to pack so many signals into a SSB BW and be able to decode each and every one of them..... Even if there is some disparity with regard to the strength of those signals.  In other words, I don't know whose signal you have been listening to, but it can't be the majority....... I am not pinging on you here, just stating fact, whether it is anecdotal or measured.  The logic of your well stated argument is good..... But experience says that the basic premise MUST be wrong.  Most of s are, indeed, producing clean signals..... The proximity of our digi "neighbors" in the digi portions of ALL the bands says so.....  :) :)

Mike A (AB7ZU)

Kuhi no ka lima, hele no ka maka

On Sep 16, 2012, at 15:14, "Tom W8JI" <w8ji at w8ji.com> wrote:

>> 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