[Milsurplus] Pi- Matching Network: When?

[C.Whitaker]

de WB2CPN
Excellent, Mike.
Another early use of the Pi was for coupling 75 Ohm coax into vertical
Low Frequency and Broadcast antennas.
When the Air Navigation facility, the LF Radio Range, was placed
into service in about the same time frame as Mike mentions, the
four vertical towers were fed from the A/N transmitter located in a
central building.  There was a "Tuning Box" at the base of each
tower, and it contained a form of a Pi network used to match the
coax to the tower, and to insure the proper tower phasing.
Trivia: A Pi network, when the Input and Output impedances are
the same, makes a good device for adjusting the RF Phase.
Been there, done that, at lots of USAF and other places.
The broadcast antennas I've seen usually had a similar arrangement.
As far as I know they still do that, but the Gates used a tapped 
inductance.
The Collins transmitter, the 32-RA, a ham radio that AF and Sig Corps
snatched in WWII, had four Pi networks in it because it had four
pre-tuned channels.
More Trivia:  Art Collins personally convinced General Curtis LeMay to
use SSB in Strategic Air Command aircraft.
73   Clete





On 2/9/2012 9:59 AM, Mike Hanz wrote:
> On Feb 7, 2012, at 5:49 PM, David Stinson wrote:
>>> Anyone have any idea when the Pi output matching
>>> network appeared?
> Looks like May 1931, Dave.  A quick google search brought out this
> article on the Windom antenna by John Nagle in the May 1978 issue of Ham
> Radio Magazine:
>
> "William L. Everitt, as faculty advisor to the students who worked on
> the antenna, contributed much to its development.  Everitt began his
> amateur career in 1914 as 2ABI; in 1921 he became 8CRI. When he decided
> to go into communications professionally, he dropped amateur radio
> because he did not want to have the same vocation and avocation.
> Everitt was later to become a prominent author and educator.  He retired
> as Dean of Engineering at the University of Illinois and went on to
> become Dean Emeritus at that university.
>
> Unfortunately, Dr. Everitt has been ill-treated by the amateur
> community.  His work on the off-center-fed antenna is largely unknown
> and certainly unrecognized.
>
> Unhappily, the same thing happened to him a second time.  *Everitt was
> the first to describe the use of a pi network as a coupling device.*  He
> published this work in the Proceedings of the IRE in 1931 (12) and in
> Communications; (13) the pi network is also described in his book,
> Communication Engineering. (14)
>
> Arthur Collins, W9CXX, of Cedar Rapids, Iowa, recognized the advantages
> of the pi network to couple the output stage of a transmitter to a
> transmission line, and used it in his transmitters. This application
> played an important part in establishing the reputation that Collins
> equipment will load up to "anything." Collins described the pi network
> to the amateur community in a QST article (15) and in a similar article
> in Radio, (16) and the network became known by old-timers as the
> "Collins Coupler" instead of, perhaps, the "Everitt Easy Loader.""
>
> References:
> 12. W. L. Everitt, "Output Networks for Radio·Frequency Power
> Amplifiers," Proceedings of the IRE, May, 1931, page 725.
> 13. W. L. Everitt, "Coupling Networks," Communications, September, 1938
> 14. W. L. Everitt, Communication Engineering, McGraw-Hill, New York,
> 1937, page 263
> 15. A. A. Collins, W9CXX, "A Universal Antenna Coupling System for
> Modern Transmitters," OST, February, 1934, page 15
> 16. A. A. Collins, W9CXX, "The Answers to the Flood of Inquiries
> Regarding the Collins Antenna System:' Radio, March, 1934, page 5
>
> John J. Nagle, K4KJ (SK)
> Herndon, Virginia
> May 1978 in Ham Radio Magazine
>
> So now you know...
> 73,
> Mike  KC4TOS
>
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