Topband: Digimodes

[Tom W8JI]

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.>>>>

The problem is almost never decoding signals near other signals of 
relatively similar levels, say within 20 dB or so of each other.

Problems almost always occur when a strong signal of what might appear to be 
reasonable purity in other cases is parked near noise floor signals. It is 
all about dB.

<<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.>>

That is probably what Collins thought, too. After all, if a dozen S6 to 
S9+10  32S1 transmitters were near each other and able to work, why would 
the FCC be sending out pick tickets, and why would other people be 
complaining about the same system? Because the other people were trying to 
work S2 -S4 signals, and the birdies and carrier were falling on them.


The same is true for NDB's with a bit too much drive. If airplanes don't 
notice a problem with an overdriven NDB at the next airport, they must be 
pretty good. Why do they bother Hams 2000 miles away?

Most 30S1's actually were around -40 dB or so for spurious, and most NDB's 
are better than that. That doesn't change the fact both systems are poor 
ideas, and cause problems that could have been avoided.

.... 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..... 
:) :) >>>>>

Most doesn't make something the best choice.  You'll find very few people 
who want to park in a neighborhood where **most** cars don't get broken 
into, when there might be a better choice.

My basic premise is exactly correct. Modes generated at baseband audio and 
transmitted through SSB transmitters are only as clean as the basic SSB 
transmitter, and are subject to operator and external wiring error. SSB 
transmitters are not especially clean, so it seems a little short-sighted to 
park S9+ signals next to S3 signals unless there is no other choice.

Also, when that 5 kHz slot (or whatever it is today) fills up, where will it 
expand? Will the digimodes push the SSB up above 1850kHz or will it push the 
CW below 1830?

160 is not at all like 80 or higher.

Placing digimode local operation between 1835 and 40 really does not show 
much foresight at all, if there is long term increased activity. Maybe 
digital mode operation will never grow, and none of this will ever be more 
of an issue than it is now.

73 Tom