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

[Paul Daulton]

Excellent answer John. I have listened to a lot of psk but rarely 
transmitted. I now have a much better appreciation of the operating 
parameters. I see too, why the psk guys prefer qrp. They get very upset 
with dirty signals. 

Thanks

Paul k5wms

Quoting John Andrews <w1tag at charter.net>:
> 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
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Paul Daulton K5WMS
beacon WMS 185.302 khz qrss30/slow 24/7
Jacksonville,Ar 72076
em34wu