aunwin wrote:
The half power thingy I presume is understood by all so IS something very
exciting to be revealed that shows that the dipole is really an efficient
radiator after all, but only if you put a class C amplifier on it?

Art, I assume you know that Class-C amplifiers are not usually used
for SSB since they are not linear for SSB. The basic confusion is
between linear systems and non-linear systems. If the amplifying
device (singular) conducts over the entire 360 degrees of an RF cycle
and the output waveform is a reasonable copy of the input waveform,
then that device is said to be linear. If you have two amplifying devices
operating in anything except Class-A operation, the output of each
individual device is not linear. That's the kicker. The "two non-linear
device" option is not available at the antenna for receiving purposes.
A normal dipole cannot receive Class-C (non-linear) signals.
--
73, Cecil, W5DXP

Reg Edwards wrote:
The internal resistance of a transmitter is NOT 50 ohms. It is not a design
feature. It is whatever happens to appear after the designer has met a
series of other requirements. The designer himself does not know what the
internal resistance is unless, out of curiosity, he bothers to measure or
calculate it.

Proving that, like 50/60 Hz AC power, efficiency may be
more important than maximum power transfer. Edison actually
thought that AC generators would burn up while trying to
deliver maximum power. That's why he backed DC.
--
73, Cecil, W5DXP

Cecil, W5DXP wrote:
"Seems to me that Ae would be in square meters."

Cecil is wide awake. If you divide watts by watts per square meter, you
end up with square meters. Appropriate for for an aperture, and
dimensionally correct.

I must have been half asleep and typed something from the wrong line.
Kraus made no mistake. I did. I apologize.

Best regards, Richard Harrison, KB5WZI

On Wed, 25 Feb 2004 12:22:32 -0600, "Steve Nosko"
wrote:

[...] you simply measure the caloric result and ignore
shape altogether.

I always thought that the common method of measuring RF power was pretty
cool! The Thermistor or bolometer. Here you balance a bridge with DC or
low freq AC. It heats the thermistor to the correct resistance. Then, when
you add RF power, the thing heats up more and changes resistance. So, you
remove some DC power to get back to the correct resistance and that amount
is easy to figure. That is how much RF you put in. Cool. I think it is
correct to say that you absolutely cannot measure power *directly*. You
must measure something else which is affected/caused by the power...comment?


Hi Steve,

There are many classes of caloric devices, two of which you identify
that are common within the Metrologist's art, and wholly absent from
amateur activities. So here I must make a slight correction of your
description. Power meters contain two (2) such devices which form the
balanced halves of a bridge. One side is exposed to the RF, the other
side is exposed to the simpler DC or AC power that is known to a high
degree of accuracy. What you describe is the detector implementation
of the same devices (which exhibit non-linearity to perform
detection). They would, in the fashion you describe, offer good
"relative" power indication, but not absolute power (except through
substitution methods). As such, they are fairly common in precision
VSWR instrumentation especially when they are driven by 1KHz modulated
power sources, and in turn drive special AC VTVM's scaled to present
dB and VSWR to very high resolution.

A list of the methods:
The Crystal: 1N21/23/25/26...
The Bolometer (low power caloric)
The Barretter (a Bolometer): Sperry 821, PRD 630A
The Wollaston wire (a Barretter): actually a 0.01A glass fuse
The Carbon filament (a Barretter)
The Thermistor (a Bolometer): Western Electric 28A
The Thermocouple
The Thermopile (lotsa Thermocouples)

73's
Richard Clark, KB7QHC

Cecil
I am talking about the half power thingy with respect to a series circuit of
which a antenna is designed around. Reg politely made a separate thread on a
specific part of that thread which referred to impedance, presumably because
Q was being bandied about where he thought probably it was irelevant.
Am I wrong to think that because a different thread was not made
the impedance question and amplifiers was relavent and somebody was not
being destructive/impolite?
Now to your pont of what is the kicker...a normal dipole cannot receive
Class-C (non linear signals)"?
Having being told about this thing that somebody read somewhere,
where is it leading to? Seems like I entered a class on engineering
and after 5 minuites I am wondering what sort of professor I had that not
only just read books out loud for his money but thought it was O.K. to read
from a wood working book. Can't we assume that a antenna is a closed series
circuit containing only passive
items ? If you have in mind that we must we consider an antena as a Class
something or other amplifier when determining its impedance then I am
hopelessly lost in a thread that can only end up nasty like some others did
and drive some more people away
because somebody wanted to play games of obstruction with the intent to
annoy. Now I see that somebody decided to change this
thread heading instead of starting a new thread . Now we are talking about
RMS meters and how they can be used ? Are we talking digital or analogue,
hand held or otherwise, high enough accuracy to satisfy all ( Nah that is
asking to much) Well it is an antenna newsgroup so it must radiate ,
somebody read it in a book and assumes that all are unaware of it so he
wishes to describe it
so others can make sense of what he read and why he read it!
Regards
Art
I am not pointing the finger at you Cecil, I have no idea who the culprit is
or what his intent is.


?Cecil Moore" wrote in message
...
aunwin wrote:
The half power thingy I presume is understood by all so IS something
very
exciting to be revealed that shows that the dipole is really an
efficient
radiator after all, but only if you put a class C amplifier on it?

Art, I assume you know that Class-C amplifiers are not usually used
for SSB since they are not linear for SSB. The basic confusion is
between linear systems and non-linear systems. If the amplifying
device (singular) conducts over the entire 360 degrees of an RF cycle
and the output waveform is a reasonable copy of the input waveform,
then that device is said to be linear. If you have two amplifying devices
operating in anything except Class-A operation, the output of each
individual device is not linear. That's the kicker. The "two non-linear
device" option is not available at the antenna for receiving purposes.
A normal dipole cannot receive Class-C (non-linear) signals.
--
73, Cecil, W5DXP

Art, KB9MZ wrote:
"The half power thingy I presume is understood by all so IS something
very exciting to be revealed that shows that the dipole is really an
efficient radiator after all, but only if you put a class C amplifier on
it?"

Art was the introducer of efficiency into this impedance thread.
Something from Art about radiation per unit length of an antenna, if I
recall. We noted that the antenna itself is usually so efficient there`s
not much to talk about, but there are differences in the effectiveness
of getting a signal on and off the air via an antenna. There`s coupling
the antenna to the radio. This has been argued here since before the "47
KW CB" thread, and that was years ago.

If Art can get more signal out of an antenna which is as small or
smaller than ordinary without putting more current into that antenna,
assuming orientation, polarization, and the other usual conditions are
fair for the competition, I`m excited.

Best regards, Richard Harrison, KB5WZI

Art, KB9MZ wrote:
"Can`t we assume that an antenna is a closed series circuit containing
only passivee items?"

Sure, but you have an incomplete representation. An antenna is coupled
more or less to the entire universe. It is usually tightly coupled to a
radio or similar apparatus by some mutual impedance which makes a
codependency.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Steve Nosko wrote:
"A (tube) amplifier is in conjugate match conditions. ...

Now assuming you can, increase the (plate) supply voltage by , say
20%---(may be the fatal flaw)."

Likely so. If everything remains linear, 20% more voltage increases
power by 1.2 squared, or 1.44 times. If the tube was already dissipating
its maximum sustainable power, expect an early failure due to the
overload.

That's what I went on to say (get more power and 50% will be
dissipated in the stage...until it blows), but there was more to the story
which is relavant.
--
Steve N, K,9;d, c. i My email has no u's.

"Richard Harrison" wrote in message
...
Steve Nosko wrote:
"Then there`s the solid-state power amplifier standard output resistance
formula.
Rs = Vcc^2 / (2*Po)
The implication should be obvious."

It looks like Ohm`s law to me, P=Vsq / R.

Well... I don't call THAT ohm's law, but rather, oh, I suppose, the
power formula, but that's symmantics. It is a transposition of (whatever
you call) that formula.



The implication of (2*Po) is that 50% of the power is in the source and
50% of the power is in the load.

Again, I don't recall teh derivation, but it works. I don't believe it
related to a mathematical constraint that the power be equally split. Can't
speculate further withoug working it out.
This is the "maximum output" load. Don't know off-hand what the limiting
factor is, but this is what they desigend for and I don't thing you could
get more out without killing the part or its lifetime. Don't recall anyone
blowing parts with the wrong load...pretty robust parts. You just couldn't
get any more out.


If so, it`s a Class-A amplifier

They are class C. VHF FM PAs.


formula, but the semiconductors could be biased to cut-off (Class-B) to
reduce dissipation in the transistors when they are idle. The best
collector load resistance is often not that which produces maximum
output, but that which produces maximum "undistorted output".

Best regards, Richard Harrison, KB5WZI

aunwin wrote:
Can't we assume that a antenna is a closed series
circuit containing only passive items ?

A passive antenna, when it is receiving a signal, is a pretty good
approximation to a Thevenin Equivalent circuit. The received
signal is the generator. The generator impedance is the radiation
resistance (and the lossy R's). We've got a transmission line and
usually a 50 ohm load in the receiver.

If you have in mind that we must we consider an antena as a Class
something or other amplifier when determining its impedance then I am
hopelessly lost in a thread that can only end up nasty like some others did

Why not, for the purposes of limiting the discussion, consider only
a Thevenin Equivalent 50 ohm source for the transmitter? That way,
the entire system will be linear and easy to discuss.

I am not pointing the finger at you Cecil, ...

If you were, which one would it be? :-)
--
73, Cecil, W5DXP