Matching , Power Transfer & Bandwidth
 

Many posts under the drifted thread "1/4 vs 1/2 wavelength antenna" give
various views on the physics of generating the maximum safe load power from
an RF amplifier. To those posters I present this reality.

Modern, solid-state FM broadcast transmitters WITHOUT TUNING OR OTHER
ADJUSTMENT will produce their full rated output power into a 50 ohm load at
any frequency in the 88-108MHz FM broadcast band, and with ~uniform, and
high PA efficiency (80% or better, typically). These transmitters have no
resonant circuits in their entire RF chain except for their output
lowpass/harmonic filter. It is possible to slew the tx freq from one end of
the band to the other in the time it takes for the exciter to lock up on the
new frequency (a second or two).

This reality seems at odds with many of the declarations made in this NG,
and perhaps may inspire some posters to further research their opinions and
theories.

RF

Visit http://rfry.org for FM transmission system papers.

Very briefly, what's the point of your apparently scary message.

Hi Richard,
You may have meant this to go to a different group,
But I must point out the resonant circuits in the output of the exciter.
Usually the exciter has an output lowpass/harmonic filter.
But you knew this anyway;)

"Richard Fry" wrote in message
...
Many posts under the drifted thread "1/4 vs 1/2 wavelength antenna" give
various views on the physics of generating the maximum safe load power
from
an RF amplifier. To those posters I present this reality.

Modern, solid-state FM broadcast transmitters WITHOUT TUNING OR OTHER
ADJUSTMENT will produce their full rated output power into a 50 ohm load
at
any frequency in the 88-108MHz FM broadcast band, and with ~uniform, and
high PA efficiency (80% or better, typically). These transmitters have no
resonant circuits in their entire RF chain except for their output
lowpass/harmonic filter. It is possible to slew the tx freq from one end
of
the band to the other in the time it takes for the exciter to lock up on
the
new frequency (a second or two).

This reality seems at odds with many of the declarations made in this NG,
and perhaps may inspire some posters to further research their opinions
and
theories.

RF

Visit http://rfry.org for FM transmission system papers.

Richard Fry wrote:
Many posts under the drifted thread "1/4 vs 1/2 wavelength antenna" give
various views on the physics of generating the maximum safe load power
from an RF amplifier. To those posters I present this reality.

Modern, solid-state FM broadcast transmitters WITHOUT TUNING OR OTHER
ADJUSTMENT will produce their full rated output power into a 50 ohm load
at any frequency in the 88-108MHz FM broadcast band, and with ~uniform,
and high PA efficiency (80% or better, typically). These transmitters
have no resonant circuits in their entire RF chain except for their
output lowpass/harmonic filter. It is possible to slew the tx freq from
one end of the band to the other in the time it takes for the exciter to
lock up on the new frequency (a second or two).

This reality seems at odds with many of the declarations made in this
NG, and perhaps may inspire some posters to further research their
opinions and theories.

RF

Visit http://rfry.org for FM transmission system papers.

Read the book _Radio Frequency Transistors Principles and
Practical Applications_, by Norm Dye and Helge Granberg. At
some point in the book, they go to great lengths dealing
with "matching" the input and output of transistors and how
to effect broadband matching schemes. They even mention some
transistors that are manufactured in such a way as to be
internally matched over a particular range of frequencies.
It doesn't hurt to read books by guys who know what they're
talking about.
73,
Tom Donaly, KA6RUH

"John Doe" wrote:
You may have meant this to go to a different group,

No, this is the group with the "1/4 vs 1/2 wavelength antenna" thread I
referenced, and all the statements under it about matching RF amps and loads
across different bandwidths.

But I must point out the resonant circuits in the output of the exciter.
Usually the exciter has an output lowpass/harmonic filter.

The practice in top-of-the-line FM systems these days is to use a harmonic
filter on the exciter output only if/when it is used as a low-power
transmitter directly on the air. Otherwise that filter is redundant, and
can reduce the performance of the exciter by a small amount.

RF

So what IS your point?...

Joe
W3JDR

"Richard Fry" wrote in message
...
"John Doe" wrote:
You may have meant this to go to a different group,

No, this is the group with the "1/4 vs 1/2 wavelength antenna" thread I
referenced, and all the statements under it about matching RF amps and
loads across different bandwidths.

But I must point out the resonant circuits in the output of the exciter.
Usually the exciter has an output lowpass/harmonic filter.

The practice in top-of-the-line FM systems these days is to use a harmonic
filter on the exciter output only if/when it is used as a low-power
transmitter directly on the air. Otherwise that filter is redundant, and
can reduce the performance of the exciter by a small amount.

RF

"W3JDR" wrote
So what IS your point?...
__________________

To show by example that circuits and transmitters exist with capabilities
said to be impossible by some posters to this newsgroup.

RF