what is qrss?
the term qrss is derived from qrs - a cw ("morse code") abbreviation that means "you are sending too fast" or "slow down." by extension, then, qrss would imply very slow sending speed.
the big question: why?
it all comes down to communications theory. the faster the signaling rate, the more bandwidth you need. the more bandwidth you have, the more energy (i.e. transmitter power) you need to keep your signal above the noise. in a nutshell this means that the faster you go, the more power you need, all other things being equal.
let's take a look at a 12 wpm cw signal for a moment. the "dit" length at this speed is approximately 1/10th of a second, so we can say that we could sent 5 dits (and 5 "inter-dit" spaces) in one second. as a general rule-of-thumb, to keep the dits from running into each other, we'd need to make sure that our "receive" system was capable of responding at about 3 times the frequency of the dit's 1/10th of a second period, or about 1/30th of a second - which is to say, about 30 hertz of bandwidth.
so, this means that if we want to receive a cw signal that is running at 12 wpm, we'd have to use a cw filter that was no narrower than 30 hz: going narrower than this will cause the "dits" will start to run together and we'll have difficulty copying the signal.
let's compare this to a standard ssb filter of, say, 2.4 khz bandwidth. this 2400 hz wide filter is 80 times wider than the 30 hz filter (for an "ideal" filter) and will let 80 times as much energy through it. since our desired cw signal only takes 30 hz of the 2400 hz, most of our receive energy is where our signal is not (assuming a signal that is near the noise level, of course) and we are at a 19db disadvantage (ignoring psychoacoustics, for the moment.)
http://www.ussc.com/~turner/qrss1.htmlhttp://www.uba.be/hf/old_qrp/qrp_2005_nl.html
