Interesting discussion, but I'm now confused.
In all the old handbooks the discussion of amplifier design says ( page
76, 1941) "In amateur transmitters, and r.f. amplifier is invariably
operated Class C ( see Chaptr 3)." I though the final tuned circuit was
simply "pulsed" at the RF freq and then the output filtering knocked off
harmonics leaving a clean CW note. And in the article on construction of
a 100-175 watt CW transmitter ( page 155-157) the 6L6 crystal oscillator
was cathode keyed with a bit of RC shaping. Rest of stages powered up
when in transmit.
And I thought these days some AM broadcast transmitters operated Class
E. Clearly not linear.
73, tom w7sua
On 7/26/2015 9:32 PM, Alan wrote:
> CW would be another mode that would not need a linear amp I think.
No, CW requires a linear amplifier. CW is not constant-amplitude - the
amplitude changes every time you open or close the key. A class-C
amplifier would mess up the key shaping, causing key clicks.
Any true FSK or MSK signal should not be bothered by a non-linear
amplifier. The only caveat I can think of is that the amplitude of an
AFSK signal may have some ripple on it to the extent that the passband
of the transmit crystal filter is not flat. But I doubt that's a
significant issue.
Alan N1AL
On 07/26/2015 06:57 PM, Tom Azlin W7SUA wrote:
Hi Don and Alan,
I was thinking one of the slow multi tone FSK modes that are a single
tone at a time. WSQ is in the same class.
http://www.qsl.net/zl1bpu/SOFT/WSQ.htm
CW would be another mode that would not need a linear amp I think.
On the other hand PSK31 would require a linear amp.
73, tom w7sua
On 7/26/2015 5:43 PM, Alan wrote:
On 07/26/2015 05:32 PM, Don Wilhelm wrote:
Soundcard sourced digital modes are really SSB signals and need a
linear
amplifier.
The one exception might be FSK. It is constant-amplitude so a class C
amplifier should be fine.
FSK modes include RTTY and I believe WSPR and WSJT.
Alan N1AL
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