wrote:
Hi,

I am looking for some help in understanding amplifier concepts (solid
state only) and product specifications. I have searched for
definitions and essays on the topic, but , having no electronics
exposure, I find it hard to understand the concepts clearly. So if
someone can please help:

1. What actually is amplification of a RF signal: is it the scaling up
of the amplitude?

In electronics, amplification of _any_ signal is it's scaling up in
amplitude or power.

I want to amplify a signal where the output has very low distortion
and noise. It should be as close to the input signal as possible:

2. Does push-pull setup mean that it's a class AB amplifier in which
two amplifiers amplify the same signal, but the opposite two halves of
the input signal?

Take out the "class AB" from your above statement, and the answer is
"yes". You can have push-pull class A or C amplifiers as well.

If this is true, in an amplifier like this:
http://www.communication-concepts.com/ar347.htm

If two solid state amplifiers are rated at 600W each, and it's a push-
pull arrangement, how come the output of this amplifier is 1000 watts
(or 1.2 kw theoretically)
If one Motorola amplifier is amplifying half the signal, the other
amplifying the other half, wouldn't the total output be 600W for the
whole signal?

There are a number of reasons for not pushing the output devices to
their limits, and there is always a certain amount of loss in the
coupling network. Just because the transistor _could_ generate 600W in
the right circuit doesn't mean that every designer _would_ make it so.

3. In class AB amplifiers, is the output signal an exact replica (but
amplified) version of the input signal?

We wish. Ideally, yes that is the case. Practically the output signal
will be filtered, delayed, and distorted but not too much.

4. What is an octave when dealing with amplifiers?

A two-times change in frequency, just like it is on a piano.

5. Is this communication concepts HF 1000 watt amplifier a class A,
class AB, or class C amplifier?
http://www.communication-concepts.com/ar347.htm

The page mentions that it's a linear amp, so it's probably class AB.
Class A would be terribly inefficient, and class C wouldn't be linear.
Communications Concepts builds amplifiers from Motorola applications
notes -- your best bet would be to find them and read what the app note
has to say. I _think_ that the high-end RF transistor line was retained
by Motorola when it spun off On semiconductor, so you probably need to
check the Freescale website (Motorola then spun off Freescale). It may
now be an On part, however. If you don't find it, ask here.

6. Does anyone know the detailed specs for this same communication-
concepts 1000 watt HF amplifier?
Specs like:
a. Duty cycle
b. Phase stability
c. Phase change with power
d. Gain flatness
e. Pulse droop
f. Harmonics
g. Spurious
h. Rise/fall times
i. VSWR or load SWR
j. Gate delay

Check the app note.

7 Can this amplifier be "controlled" to give graded amplification less
than 1000 watts specified, or will it work only at this maximum level?

The amplifier is linear, so it will have a more or less fixed
amplification. To get less power out in it's linear region, just put a
smaller signal in.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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"Applied Control Theory for Embedded Systems" gives you just what it says.
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