Welcome to the group, Wes. That is an interesting question, I look forward to seeing other answers.
My answer is rather vague and generalized . I'm going to argue that "reduced power" is not really the issue, but that reduced power is often associated with no ALC which most point out is a key in not having a over-driven, distorted , signal . I say "most" because not every ham agrees with this, some thing ALC is not that much of a factor. The prevailing view is that most soundcard modes should not be showing ALC, PSK31-250, Olivia, AFSK ,RTTY, etc, but some modes like JT65A are less prone to this issue. FSK RTTY is also not a mode that would be impacted by this issue. Consider this from "PSK Fundementals" by Peter G3PLX (http://aintel.bi.ehu.es/psk31theory.html). Also see http://www.eham.net/articles/12626 The Good Bad and Ugly on PSK31. "There is a problem with PSK keying which doesn't show up with FSK, and that is the effect of key-clicks. We can get away with hard FSK keying at moderate baudrates without generating too much splatter, but polarity reversals are equivalent to simultaneous switching-off of one transmitter and switching-on of another one in antiphase: the result being keyclicks that are TWICE AS BAD as on-off keying, all other things being equal. So if we use computer logic to key a BPSK modulator such as an exclusive-or gate, at 31 baud, the emission would be extremely broad. In fact it would be about 3 times the baudrate wide at 10dB down, 5 times at 14dB down, 7 times at 17dB down, and so on (the squarewave Fourier series in fact) The solution is to filter the output, or to shape the envelope amplitude of each bit which amounts to the same thing. In PSK31, a cosine shape is used. To see what this does to the waveform and the spectrum, consider transmitting a sequence of continuous polarity-reversals at 31 baud. With cosine shaping, the envelope ends up looking like full-wave rectified 31Hz AC. This not only looks like a two-tone test signal, it IS a two-tone test signal, and the spectrum consists of two pure tones at +/-15Hz from the centre, and no splatter. Like the two-tone and unlike FSK, however, if we pass this through a transmitter, we get intermodulation products if it is not linear, so we DO need to be careful not to overdrive the audio. However, even the worst linears will give third-order products of 25dB at +/-47Hz (3 times the baudrate wide) and fifth-order products of 35dB at +/-78Hz (5 times the baudrate wide), a considerable improvement over the hard-keying case. If we infinitely overdrive the linear, we are back to the same levels as the hard-keyed system. " Andy K3UK --- In digitalradio@yahoogroups.com, "w1...@..." <w1...@...> wrote: > > Greetings. > > I am Wes W1LIC in Bangor, ME and just joined this group. I run a Kenwood > TS-480SAT to vertical or dipole antennas. I have an old HP desktop running > XP and use either the FLDIGI or PSKExpress software. > > Although I've been a ham since 1967, I am a newbie to the digital modes. CW > has always been my primary mode of operation. I've had several contacts via > PSK31, but now am interested in trying other modes. This week I had my first > contact via OLIVIA, which seems to be a very interesting mode. > > I've always heard and read that on PSK31 we should greatly reduce our power > and not show any ALC indication when transmitting. Does this same advice > hold true for Olivia and other digital modes as well? I'd appreciate input > from some of you more experienced digital ops. > > Wes W1LIC >
