Topband: Digimodes

[Mike Armstrong]

Tom, actually I DID say with varying signal strengths.  The difference being IF the agc is badly pumped by a strong station and the weak station is wiped out by the action.  I can easily decode a weak station next to a strong one, as long as the agc is being pumped by the stronger station to the point that the weaker can no longer be heard.  It has nothing to do with a distorted signal.

In that regard, by the way, it is very likely that the stronger station will be the CW one, not the psk one.  Normally, psk ops occur well below the maximum output of the average transceiver in pursuit of a cleaner signal.  Once the agc is engaged, the linearity required for phase shift keying is likely gone.  So the knowledgable psk'ers keep their rigs down i  the 30 watt arena. 

Now, again, I never said planting the digi portion in 35-40 was a good idea.  It isn't!  It isn't a good idea for folks to make no room for intercontinental ONLY qso's.  In my humble opinion, general use of that area is bad juju no matter the mode.  And, yes, adding general use digi to that area is a bad idea for the same reason...... UNLESS they are pursuing an intercontinental qso.  Again, that is just my opinion and only MY opinion as far as I can tell.

If you recall, one of my earliest points was that WE, repeat WE should be the ones making band plans for 160.  The reason being obvious.... WE, as the users of that spectrum, understand that band better than ANY organization of people who never visit it.  I am certainly not picking onmthe ARRL or RSGB or any other ham org..... Just sayin' that WE should come up with an inclusive band plan that takes digi (including, in particular, DX digi pursuits) and get some of the heavyweights on 160 to bless it.  Once that is done, it should be a piece of cake to get the ORGs to follow suit....... i would hope, anyway  :)

Mike A (AB7ZU)

Kuhi no ka lima, hele no ka maka

On Sep 16, 2012, at 17:28, "Tom W8JI" <w8ji at w8ji.com> wrote:

> 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