1/4 vs 1/2 wavelength antenna

[Larry Brasfield]

The phrase "output impedance" in connection with amplifiers is ambiguous and
likely to result in arguments.

I suppose the same could be said of any block that is
susceptible to having some feedback put around it.
Therefore the term "output impedance" should never
be used at all. And of course, any term that could, or
has ever been known to lead to an argument, with any
uninformed person that might come along, should be
eliminated from our vocabulary.

Uuugh. Mmmmph. Me drag woman to cave by hair.

The correct description is "internal impedance" or "internal resistance" and
should always be used.

Nonsense.

If I wanted to speak of an impedance inside of some
circuit, I might loosely speak of it as "internal", but in
any useful discussion, it would be spoken of as either
an output impedance or an input impedance, and, with
most people I have such discussions with, there would
be no need to add that some unknown additional feed-
back not part of the present discussion could alter the
observable impedance.

I hope your post was a troll.

 

[John Woodgate]

I'm sorry, but they are not. Nor are any power amps that I know of.
Efficiency (and thus necessarily output swing) is what matters for power
amps. To maximize swing requires load line matching, not impedance
matching.

What is a 'load line'? A straight line on an I/V graph? What does the
gradient of that line represent?

 

[John Woodgate]

I read in sci.electronics.design that Larry Brasfield <donotspam_larry_b

If I wanted to speak of an impedance inside of some circuit, I might
loosely speak of it as "internal", but in any useful discussion, it
would be spoken of as either an output impedance or an input impedance,

The problem is that people say 'output impedance' when they mean 'load
impedance'. To prevent misunderstanding I use the term 'output source
impedance'.

There are also some people who use 'input impedance' when they mean
'source impedance'. I don't talk to them. (;-)

 

[Rich Grise]

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.

Apparently, I'm not following the same conversation here, because I
thought that the impedance matching network (in the instant example, the
pi-net output of the transmitter) was what translated the load impedance
to the source impedance, matching both in the process.

Thanks,
Rich

 

[Rich Grise]

Uuugh. Mmmmph. Me drag woman to cave by hair.

Uh. Nuh. Drag _FROM_ hair.

 

[Airy R.Bean]

My "Bailey" amps (Wireless World c. 1970) have lots
of internal resistances, all soldered in neatly by hand.

In your comment below, I think that you have "output"
much "impudance".

 

[Cecil Moore]

Apparently, I'm not following the same conversation here, because I
thought that the impedance matching network (in the instant example, the
pi-net output of the transmitter) was what translated the load impedance
to the source impedance, matching both in the process.

Maybe I inferred wrong. From your "load line equals
impedance" statement above, I inferred that you were
implying that the load line *is* the source impedance.

 

[Allan Herriman]

The phrase "output impedance" in connection with amplifiers is ambiguous and
likely to result in arguments.

The correct description is "internal impedance" or "internal resistance" and
should always be used.

S22 is fairly well defined.

Allan

 

[Rich Grise]

Maybe I inferred wrong. From your "load line equals
impedance" statement above, I inferred that you were
implying that the load line *is* the source impedance.

No, just trying to make the point that it does, in fact, _have_ an
impedance. (even if it's running class E.) What that exact impedance is,
of course, is left as an exercise for the reader.

And another thing - in a transmitter, the impedance matching only happens
at the one frequency, which is a lot different scenario from, say, a
stereo. This could be a confusion factor here.

Thanks,
Rich

 

[Cecil Moore]

S22 is fairly well defined.

What's the S22 of an IC-756PRO?

 

[Cecil Moore]

S22 is fairly well defined.

What's the S22 of an IC-756PRO? With that figure,
S22^2 is defined as:

Power reflected from the network output divided by
Power incident on the network output.

Better yet, we can then calculate the reflected power
dissipated by the IC-756PRO.

 

[Cecil Moore]

And another thing - in a transmitter, the impedance matching only happens
at the one frequency, which is a lot different scenario from, say, a
stereo. This could be a confusion factor here.

Therefore, the key to converting the non-linear source to
an equivalent linear source lies in a Fourier analysis?
Do the other-than-fundamental terms in the Fourier analysis
encounter a low impedance or a high impedance?

 

[John Woodgate]

I read in sci.electronics.design that Cecil Moore <[email protected]>
wrote (in <[email protected]>) about '1/4 vs 1/2 wavelength antenna',

Therefore, the key to converting the non-linear source to
an equivalent linear source lies in a Fourier analysis?
Do the other-than-fundamental terms in the Fourier analysis
encounter a low impedance or a high impedance?

Yes. Not facetious; the impedance matching network can be configured to
minimise individual or a few harmonic emissions by adjusting its
impedances at harmonic frequencies. Either high or low (or perhaps both)
can minimise the emission, depending on the configuration.

 

[Reg Edwards]

What's the S22 of an IC-756PRO?

=============================

Cecil, I havn't the foggiest idea what an IC-756PRO is except that it is
something which comes from that excellent manufacturer Icom.

But your extremely brief question is the most hillarious ever asked on this
newsgroup. You are still at the best of your form. I can't stop laughing.

The best I could do is ask what is the S22 of a 6J5. One thing for certain,
it is not mentioned in manufacturer's data sheets. Yet ARRL simple PA design
rules manage very well without it.

 

[Ken Smith]

Let's assume the designer is an amateur who didn't provide
any protection for his tube's output. The lower the resistive
load, the more current the output device draws until it fails.
What is the output impedance of the device?

At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.

 

[Ken Smith]

SWR foldback is part of impedance matching?

Yes for the purposes of the OP's case it is. He is trying to use an
existing transmitter design and a hunk of wire. This seems to be the part
of my argument that people are missing. I suggested he use a matching
network to match the wire to the transmitter's output.

 

[Cecil Moore]

Yes. Not facetious; the impedance matching network can be configured to
minimise individual or a few harmonic emissions by adjusting its
impedances at harmonic frequencies. Either high or low (or perhaps both)
can minimise the emission, depending on the configuration.

Whether the harmonic impedance is high or low would affect
the efficiency, no?

 

[Cecil Moore]

At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.

Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?

 

[John Woodgate]

I read in sci.electronics.design that Cecil Moore <[email protected]>

Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?

If the FM is what passes for music these days, it's MUCH better IMHO.
(;-)

 

[John Woodgate]

I read in sci.electronics.design that Cecil Moore <[email protected]>

Whether the harmonic impedance is high or low would affect
the efficiency, no?

I think the question can only be answered by 'It depends..'. For
example, it is 'affected' if it's changed by 1%, but is that
significant?