wrote:
Back in July I wrote:

I'm reading David Rutledge's excellent "The Electronics of Radio."
In Chapter 10 -- Power Amplifiers, he discusses Class C amps and says,
"In addition, if we drive the transistor clear to saturation, using the

transistor as a switch, the dissipated power can be greatly reduced,
because the saturation voltage is low. This is Class C
amplification..."
I'd always throught that in Class C, while you'd operate the device so
that it was cutoff during most of the cycle, but not saturated.
Is this just a different definition of Class C?
I checked back with SSDRA and EMRFD, and didn't see anything about
driving Class C amps into saturation?
What says the group? Do we saturate in Class C or not?
--------------------------------------------------------
I've been thinking about this some more. The 1980 ARRL handbook points
out that "Solid State power amplifiers should be operated just below
their saturation points for best efficiency and stability." Also, the
formula that we use to determine load resistance (Rl=Vcc^2/2Po) implies
that we are looking for a combination of Vcc, Load resistance and power
out that will prevent saturation.
And wouldn't we end up with far lower harmonic content if we only clip
one side of the wave form (at cutoff) instead of both sides (cutoff and
saturation)?

I know there are more exotic modes beyond C, but for plain old ordinary
ham radio applications, don't we normally avoid saturation in Class C
amps?

Also, what about this business of having the efficiency improve through
saturation "because the saturation voltage is low" Could that be
right? If you put a voltage across a conductor and generate a large
current, you can't sit back and say "Great! Power consumption across
the conductor is low because the voltage drop across it is now
minimal!"

73 from London
Bill M0HBR N2CQR CU2JL
http://www.gadgeteer.us


As far as I'm concerned... saturation has nothing to do with the class
the amplifier is running. I can saturate an amplifier in any class.
Saturation is most ofen an undesireable effect... that causes
distortion in amplifiers.

www.telstar-electronics.com

ORIGINAL MESSAGE:

On 5 Nov 2006 10:26:11 -0800, "Telstar Electronics"
wrote:

Saturation is most ofen an undesireable effect... that causes
distortion in amplifiers.

------------ REPLY FOLLOWS ------------

Saturation is only undesirable in LINEAR amplifiers. In non-linear
amps which are often used for CW, RTTY or FM, saturation is good
because it improves efficiency. Distortion in those applications is
unimportant.

Bill, W6WRT

"Telstar Electronics" wrote in
ps.com:

wrote:
Back in July I wrote:

I'm reading David Rutledge's excellent "The Electronics of Radio."
In Chapter 10 -- Power Amplifiers, he discusses Class C amps and says,
"In addition, if we drive the transistor clear to saturation, using the

transistor as a switch, the dissipated power can be greatly reduced,
because the saturation voltage is low. This is Class C
amplification..."
I'd always throught that in Class C, while you'd operate the device so
that it was cutoff during most of the cycle, but not saturated.
Is this just a different definition of Class C?
I checked back with SSDRA and EMRFD, and didn't see anything about
driving Class C amps into saturation?
What says the group? Do we saturate in Class C or not?
--------------------------------------------------------
I've been thinking about this some more. The 1980 ARRL handbook points
out that "Solid State power amplifiers should be operated just below
their saturation points for best efficiency and stability." Also, the
formula that we use to determine load resistance (Rl=Vcc^2/2Po) implies
that we are looking for a combination of Vcc, Load resistance and power
out that will prevent saturation.
And wouldn't we end up with far lower harmonic content if we only clip
one side of the wave form (at cutoff) instead of both sides (cutoff and
saturation)?

I know there are more exotic modes beyond C, but for plain old ordinary
ham radio applications, don't we normally avoid saturation in Class C
amps?

Also, what about this business of having the efficiency improve through
saturation "because the saturation voltage is low" Could that be
right? If you put a voltage across a conductor and generate a large
current, you can't sit back and say "Great! Power consumption across
the conductor is low because the voltage drop across it is now
minimal!"

73 from London
Bill M0HBR N2CQR CU2JL
http://www.gadgeteer.us


As far as I'm concerned... saturation has nothing to do with the class
the amplifier is running. I can saturate an amplifier in any class.
Saturation is most ofen an undesireable effect... that causes
distortion in amplifiers.

www.telstar-electronics.com


Don't worry about saturation. CB'ers think over saturation produces
a better sounding signal. Of course, on ham radio we would call
them Lids.

SC

"Telstar Electronics" wrote in message
ps.com...
wrote:
Back in July I wrote:

I'm reading David Rutledge's excellent "The Electronics of Radio."
In Chapter 10 -- Power Amplifiers, he discusses Class C amps and says,
"In addition, if we drive the transistor clear to saturation, using the

transistor as a switch, the dissipated power can be greatly reduced,
because the saturation voltage is low. This is Class C
amplification..."
I'd always throught that in Class C, while you'd operate the device so
that it was cutoff during most of the cycle, but not saturated.
Is this just a different definition of Class C?
I checked back with SSDRA and EMRFD, and didn't see anything about
driving Class C amps into saturation?
What says the group? Do we saturate in Class C or not?
--------------------------------------------------------
I've been thinking about this some more. The 1980 ARRL handbook points
out that "Solid State power amplifiers should be operated just below
their saturation points for best efficiency and stability." Also, the
formula that we use to determine load resistance (Rl=Vcc^2/2Po) implies
that we are looking for a combination of Vcc, Load resistance and power
out that will prevent saturation.
And wouldn't we end up with far lower harmonic content if we only clip
one side of the wave form (at cutoff) instead of both sides (cutoff and
saturation)?

I know there are more exotic modes beyond C, but for plain old ordinary
ham radio applications, don't we normally avoid saturation in Class C
amps?

Also, what about this business of having the efficiency improve through
saturation "because the saturation voltage is low" Could that be
right? If you put a voltage across a conductor and generate a large
current, you can't sit back and say "Great! Power consumption across
the conductor is low because the voltage drop across it is now
minimal!"

73 from London
Bill M0HBR N2CQR CU2JL
http://www.gadgeteer.us


As far as I'm concerned... saturation has nothing to do with the class
the amplifier is running. I can saturate an amplifier in any class.
Saturation is most ofen an undesireable effect... that causes
distortion in amplifiers.

www.telstar-electronics.com


It can be messy. The class of amplifier is determined by the cut-off (or
lack thereof). A class A amplifier neither hits saturation nor hits
cut-off. Maximum theoretical efficiency (of a sinusodal waveform) of a
class A amp is 50%, but 25% is typical. Very low distortion, of course.

Class B amplifiers are biased at cutoff and only conduct for 50% of the
cycle. They shouldn't saturate, however. Efficiencies are around 60%.

Class C amps are typically biased well into cut-off and only conduct for
perhaps 90 degrees (25%) of the cycle and can run 70% efficient.

However, there are class D and E amplifiers and they are switchmode
amplifiers. They run on or off (cut off or in full saturation). They are
normally used for CW or FM and there was a circuit (and components)
available from a university to build a cw transmitter using switchmode. The
thing ran about 93% efficient!

To add to the confusion, with solid state it *is* possible to use the darn
things as a *linear* amplifier! Yep, commercial radio stations now use
these things. The problem is that the control circuitry (which, I believe,
controls the voltage fed to the final) is very complex and expensive and
will be found neither in amateur nor cb equipment for a long time.

73 from Rochester, NY
Jim