On Wed, 23 May 2007 23:33:45 -0400, "Jimmie D"
wrote:

Giving W8QUR the benifit of the doubt
is like saying a 4 cylinder Hummer's efficiency would be improved if
you removed the chassis.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Wed, 23 May 2007 23:33:45 -0400, "Jimmie D"
wrote:

Giving W8QUR the benifit of the doubt
is like saying a 4 cylinder Hummer's efficiency would be improved if
you removed the chassis.

73's
Richard Clark, KB7QHC

You either have to give the benifit of the doubt to W8QUR or the origonal
poster
W8QUR had benifit of editors that reviewed his work and decided it was
correct. Saying that a Pi-net is as inefficent as the OP interpretted W8QUR
as saying is a huge blunder that I doubt anyone who has the credentials to
author a magazine article would make. The OP only assumed he was talking
about Pi-networks and admitted
W8QUR did not directly refer to the network as this even though in 1965 it
was still called a Pi-net. It is also uncommon to call a pi-net a "system".
While you cant be sure unless you have the origonal article in its entirity
I will put my money on W8QUR in this case.

Jimmie

On Sat, 26 May 2007 11:15:06 -0400, "Jimmie D"
wrote:

You either have to give the benifit of the doubt to W8QUR or the origonal
poster

Hi Jimmie,

This is absurd on the face of it. Nearly every poster has performed
nothing more than "tea leaves reading" to massage inferences into
actualities. Look at the subject line heading every post and respond
to THAT. I've see nothing in three days that has diverged from my
initial response.

To mold supposed quotes into a new text that conforms to conventional
thinking does not confer nobility on the source. Using loose
references is, however, the staff of life in this forum.

73's
Richard Clark, KB7QHC

Jimmie D wrote:
"Richard Clark" wrote in message
...

On Wed, 23 May 2007 23:33:45 -0400, "Jimmie D"
wrote:


Giving W8QUR the benifit of the doubt

is like saying a 4 cylinder Hummer's efficiency would be improved if
you removed the chassis.

73's
Richard Clark, KB7QHC


You either have to give the benifit of the doubt to W8QUR or the origonal
poster
W8QUR had benifit of editors that reviewed his work and decided it was
correct.

Hmmm.. but the editors at QST and similar magazines actually don't do
that much technical review. Sometimes there are typos that don't get
caught, as well. There are several instances of incorrect or misleading
data in a QST article in the last few years (and, I suspect, if one took
the time to go back and look in decades gone by, you'd find errors there
as well). Sometimes it gets corrected in a subsequent issue, sometimes
not.

QST isn't a peer reviewed technical journal. Lots of good ideas, but
it's always wise to look at some background info too.

Jim, W6RMK

"Jimmie D" wrote in message
...

"Owen Duffy" wrote in message
...
wrote in :

Ralph Hanna, W8QUR, in a brief article "Pi Networks" on page 108 of
the December, 1965, issue of 73 MAGAZINE, after discussing power-
supply filters and high- and low-pass TV filters, wrote:

(Paraphrasing) "The most popular of all pi networks is the output
circuit of a transmitter ... with which the output of almost any
transmitter can be matched to almost any antenna ... another
advantage is the reduction of harmonics....

(Actual quote) "The big disadvantage of this system is the low
efficiency. It is not possible to run more than 50% efficiency
and it tends to be more like 30%. Other methods of feeding the
antenna will result in efficiencies of as high as 65% to 70%."

Is that "low efficiency" of 30-50% really true?


Myron,

The temptation is to see that the second paragraph is about Pi networks,
though it doesn't actually use the term. It does refer to a "system" and
goes on to discuss efficiency in the context of "feeding the antenna".

There is no doubt that practical Pi networks in transmitters operate at
efficiencies much greater than 50%, and the design efficiency is a
trade-
off with harmonic suppression (for the low pass configuration in a
typical PA).

If the term "system" is to include more than just the Pi network, then
lower system efficiciency will prevail, but without a clear definition
of
the "system", it is not possible to comment on the reasonableness. For
example, if a Pi coupled transmitter feeds a full wave dipole via a
substantial length of coax, system efficiency might well be much less
than 10%. Does he include DC to RF conversion loss in his view of system
efficiency?

Owen

Giving W8QUR the benifit of the doubt
I thought he may be including feedline losses which could be from 1 to 2
db
for coax compared to balanced line used with a balanced output network.
I think something may be lost in the paraphrasing and this is probably a
comparison of balanced to unbalanced systems rather than a comparison of
Pi-net to other types of tuner networks.

Jimmie



In the 1960's it was common to refer to efficiency as relating to the entire
system converting AC or DC power into RF out of the antenna. Total system
efficiencies of 30-50% would have been normal taking into account the losses
involved in running valve heaters, HT valve supplies and final stage cooling
fans. The reference to Pi matching output circuits is a bit of a red
herring. These were probably the most commonly used system used to match
transmitters that were required to operate on a wide range of frequencies
because they were so effective at this task, and relatively cheap to
manufacture. Other more efficient matching methods could be used for fixed
frequency valve transmitters.

Even up to the 1980's, many shipboard emergency transmitters were valve
based. Radio Officers were required to make regular checks and efficiency
calculations to ensure that the emergency transmitters and receivers could
operate for a minimum specified period from a bank of emergency batteries.
Even with several hundred amp hours of battery capacity, only around 16
hours of full power (100watts) operation was the maximum that could be
expected.

Mike G0ULI

wrote:
Is that "low efficiency" of 30-50% really true?

50 ohm solid-state transceivers have a fixed filter
on their outputs which is often a multi-stage pi-
network. That fact alone should answer the question.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
wrote:
Is that "low efficiency" of 30-50% really true?

50 ohm solid-state transceivers have a fixed filter
on their outputs which is often a multi-stage pi-
network. That fact alone should answer the question.

Doesn't the impedance transformation
ratio have an effect on the efficiency
of a pi network?

Chuck

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Chuck wrote:
Doesn't the impedance transformation ratio have an effect on the
efficiency of a pi network?

The question is not: Can a particular pi-network plus
load be 30-50% efficient? Certainly, it can. The question
is: Are all pi-networks 30-50% efficient? The answer is "No!".
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Chuck wrote:
Doesn't the impedance transformation ratio have an effect on the
efficiency of a pi network?

The question is not: Can a particular pi-network plus
load be 30-50% efficient? Certainly, it can.


No disagreement, Cecil. My question
wasn't intended as a response to your
post. Sorry about that.

The question
is: Are all pi-networks 30-50% efficient? The answer is "No!".

If that is the question, then no
disagreement there either.

We don't know all of what W8QUR said,
and none of what he meant, but there are
contexts in which each of his three
assertions could be correct. I guess the
one thing he doesn't seem to have said
is that all pi-networks are 30-50%
efficient. ;-)

73,

Chuck





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Chuck wrote:
No disagreement, Cecil. My question wasn't intended as a response to
your post. Sorry about that.

Didn't mean to sound grouchy - it was before my first cup
of coffee.

We don't know all of what W8QUR said, and none of what he meant, but
there are contexts in which each of his three assertions could be
correct. I guess the one thing he doesn't seem to have said is that all
pi-networks are 30-50% efficient. ;-)

We do know what seemed to be inferred about the inference
of what W8QUR said. :-)
--
73, Cecil, w5dxp.com