On 12/29/2011 02:09 PM, richard courtway wrote:
> Have been enjoying and learning from the discussions concerning IMD
> problems with SSB signals and their causes.
>
> Personally am a cw operator - and hear quit a few very wide and
> splattering cw signals . Thinking that most of this is caused by
> operators trying to get a kw out of a 800 watt rig. Overdriving - etc.
>
> Am approaching the time when I will have my first amp on line - and
> wondering if any of you would care to comment on the causes of such
> lousy sounding cw signals.
The CW keying waveform at the transceiver has a controlled rise and fall time to
limit key clicks. A linear amplifier will track the rise and fall time cleanly
and the
level of key clicks will remain the same. But, if the amplifier is operated in
class C,
it becomes like a switch, no output until the input rises to a certain level
and
then
a rapid rise to full output. This makes the leading and falling edge steeper
and
the faster rate of rise translates to a wider signal.
Another affect to consider is the ALC loop. If the transceiver is set to
overdrive
the amplifier, with ALC acting to reduce drive. then the ALC loop transient
response
controls the leading edge of the dit or dah. This can mean overshoot, or
almost
anything.
Any amplitude modulation of a carrier, such as from keying has a bandwidth set
by the modulation frequency components. CW uses square wave modulation
and would have a lot of odd harmonics, except for the bandwidth limiting
effect of the rise and fall time. So, even CW needs a linear amplifier to
reproduce
the waveform.
jeff, wa1hco
>
> Thankee - and HNY to you all.
>
> de Dick / aka N7RC
>
>
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