[Lowfer] 1 watt in class & quot; AB & quot; into 32 Ohm load, BW - 600 KHz, and it's an audio amp

[John Andrews]

Paul,

PSK31 uses carefully shaped amplitude keying to minimize sidebands, and 
that shaping must be preserved through the whole system, or the 
sidebands come back, and the signal is too wide for use in congested ham 
bands. WOLF does much less shaping, and is noticeably wider, even though 
the bit rate is 1/3 of PSK31.

 From G3PLX's initial write-up 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."

You might want to look at ZL1BPU's site for descriptions of the pains he 
went through to avoid having to do amplitude-shaping of CMSK and MFSK: 
http://www.qsl.net/zl1bpu/

BUT, let me make the same point that Jay made: For Part 15 operation at 
1750 meters, you can use whatever scheme you want, and probably nobody 
will be affected. One possible exception would be if you or the 
next-door neighbor like to listen to AM broadcast radio, and the 
key-clicks are bad enough to bother weaker signals at the low end of the 
band. I had that situation with TAG's WOLF operation up in Maine, and 
cured it with some shaping on the 24V line to the outside PA.

John, W1TAG