[Amps] MOSFET amp filtering - was: auto-tune

[sm0aom at telia.com]

The confusion of "Morse" and "CW" is quite typical for amateur radio, where homemade definitions abound.

>From the beginning, "CW" was a technical feature of the transmitter to discern it from a transmitter that generated "spark" or damped waves, which later got the emission class "B". The only way to modulate a spark transmitter in a meaningful way was by on-off keying using the Morse alphabet.

When the vacuum-tube oscillator became practical, the spark transmitters quickly faded into obscurity (except as a ship's emergency transmitter),
and the Morse code became sent by on-off keying of a CW signal. Still, the modulation was Morse.

For some reason, the transmitter characteristic of being able to generate a CW signal and the Morse on-off modulation came to be 
used interchangeably by amateur radio in particular.

Professional radio operators and engineers have since very long referred to Morse modulated continuous wave emissions as "A1" or just "telegraphy".

"ICW" was mentioned previously. 

It was an intermediate waveform that was used in maritime radio before receivers with beat oscillators became commonplace 
which enabled them to receive unmodulated signals, and was emulating the class B emission from a spark transmitter for interoperability reasons. 

ICW had only a short period of use, primarily at shore stations whose transmitters had been modified from spark to vacuum tube.

For the same reason, the emission prescribed on the 500 kHz maritime distress and calling frequency up to the end of the "old system" in 
February 1999 was A2A or tone modulated Morse code emissions.

73/
Karl-Arne
SM0AOM


----Ursprungligt meddelande----
Från : manfred at ludens.cl
Datum : 2016-12-16 - 13:43 (UTC)
Till : amps at contesting.com
Ämne : Re: [Amps] MOSFET amp filtering - was: auto-tune

I also shudder somewhat when I see a Morse code transmission referred to 
as "continuous wave".

 > That amateurs (and the entire commercial radio industry) called
 > on/off keyed telegraphy "continuous wave"....

Only the radio industry does. The semiconductor industry doesn't. When 
you look into the datasheet of an RF MOSFET and you see information 
given for "CW" operation, they indeed usually mean a continuous wave 
without any amplitude modulation, rather than an interrupted one. When 
they _don't_ say CW, they mean pulsed service, usually with rather short 
pulses and low duty cycles. The small print usually tells about the 
pulse duration and duty cycle.

A similar confusion arises with "class AB". Hams think of class AB as 
being reasonably linear, and used for almost all "linear" amplifiers. 
Instead the LDMOSFET datasheets usually don't use it that way! When you 
see an LDMOSFET data sheet stating an efficiency like 80% in class AB 
service, they mean saturated class AB, which gives up linearity in favor 
of efficiency and maximal output. After all, the only thing "class AB" 
means is that the active device conducts for more than 180 but less than 
360 degrees. "Class AB" doesn't tell whether or not the device is driven 
into saturation. Neither does it tell how much linearizing feedback is 
used, if any.

LDMOSFETS are run in class AB rather than class C, even when linearity 
isn't required. The reason is that their gates can't take much negative 
voltage. But for nonlinear, high efficiency amplifiers, saturated class 
AB with minimal or no negative feedback is used. This is simply called 
"class AB" in the datasheets, and does _not_ tell at what ratings to use 
that LDMOSFET in linear service!

Life is full of pitfalls...

Manfred

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