Are pi networks THAT INefficient?
 

On May 23, 7:37 am, wrote:
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, W0PBV.
--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license


Does that author bother to explain WHY he thinks that to be true?
Where exactly is the power lost? Given that pi-coupled class-C vacuum
tube output stages commonly run 75% and higher efficiency, he's
immediately proven wrong by example. I'm assuming that you haven't
left out some important context from the quotation. It's usual now,
as it was in 1965, to get at least 75% efficiency, and possible to get
well above that, using a pi output network; that depends more on the
operating conditions for the output stage than on the output network
itself. It would be interesting to hear why W8QUR thought to write
that statement about efficiency. It would also be interesting to know
if his article elicited letters-to-the-editor wondering about that,
back then.

Cheers,
Tom

Are pi networks THAT INefficient?
 

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

Does that author bother to explain WHY he thinks that to be true?

No. That's why I was surprised enough to ask the newsgroup.


Given that pi-coupled class-C vacuum tube output stages commonly run
75% and higher efficiency, he's immediately proven wrong by example.

Good point!


I'm assuming that you haven't left out some important context from
the quotation...

It was only a half-page article in a small-format magazine in the first
place, and I did not leave out anything significant!


It would be interesting to hear why W8QUR thought to write that
statement about efficiency. It would also be interesting to know
if his article elicited letters-to-the-editor wondering about that,
back then.

We'll probably never know. That was 40+ years ago, and W8QUR isn't
in the online callbook, so it will be hard to ask him. At one time
I read the following issues and don't remember any comments or
corrections, but that was a long time ago!
--
--Myron A. Calhoun, W0PBV.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license