1300 Frenchtown Road
East Greenwich, RI 02818 USA
Frederick Jaggi, President
|Wireless communication began about 1900. The first application was marine communications and this called for wireless telegraph stations on the shore. An excellent example of one of the earliest coast stations is PJ at The New England Wireless and Steam Museum.
PJ, for Point Judith, RI, (south west of Newport) mainly served passenger steamboats traveling between New York City and New England cities. PJ was built by Walter Wentworth Massie who was a contemporary of Marconi's. By a fortuitous combination of circumstances PJ's 1907 building is unaltered and still contains its original equipment in working order.
PJ was moved to the New England Wireless and Steam Museum in 1983 to avoid demolition. It is an important part of the museum which is devoted to teaching engineering history. In the museum's collection there is also much century old documentation of The Massie Wireless Telegraph Company. PJ shows the beginning of today's vast telecommunication/information complex. All Radio, TV, Sat Comm., Cell Phone, FAX, in short the information/communication industry grew from wireless stations such as PJ.
| The Massie Station's historic value is enormous and it is now listed in the National Register of Historic Places.
|The January issue of QST magazine contains an article on the Massie
|The photo shows the Massie spark transmitter under restoration. All of the original equipment is in the station except the change-over switch which was assembled by Alan Douglas from original parts. The pump handle key, Massie Resonaphone tuner and operator call box are on the original table.
The helix and straight spark gap are on top of the condenser cabinet. On the left wall above the helix are a hot wire ammeter and anchor gap.
Bert Pine donated 100 sheets of 18" square 1/8" glass and Michael Thompson has made 70 of the 100 glass plate condensers that fit in the cabinet below the spark-gap and helix. Rolf Richter cast new zinc spark gap electrodes, machined new electrode holders, and even had the machined parts nickel plated. The original high-voltage cables had bright green woven cloth insulation.
Dave and Judi Kernan made a covering for the new high-voltage cables that closely matches the appearance of the originals. We used a Marconi 2 KW spark coil because we don't have a Massie coil or information on the design of a Massie coil. We made a key relay using a Massie wooden parts box to make the pump-handle key safer to use during demonstrations. The transmitter now makes big sizzling sparks! We will not connect an antenna to the transmitter so we can keep the FCC happy. This is one of the oldest working wireless transmitter in the world.
We currently have about 0.05 mF of capacitance so the transmitter operates at about 350 KHz. It will operate at about 300 KHz when the remainder of the condenser plates are installed.
If you want to hear what it would sound like click here. (Sound file courtesy of John S. Belrose.)
|This is a close-up of the helix with a straight spark gap inside and the hot wire ammeter on the wall. Rolph Richter cast the zinc spark gap electrodes and machined the new electrode holders.
The theory behind the transmitter is simple. The high-voltage coil and capacitor are connected in parallel. The helix coil and spark gap are connected in series and the pair are connected in parallel with the capacitor. The high-voltage coil charges the capacitor. When the voltage on the capacitor reaches the breakdown voltage of the air between the spark electrodes the spark jumps between the electrodes. This makes a L-C circuit that oscillates at 350 KHz. Since some of the energy is lost in the spark the amplitude of the sine wave in the L-C circuit diminishes. This is called a damped oscillation and is shown in the image below. Since the high-voltage coil is driven by AC, one 1/120 of a second later the circuit is charged and sparking again.
|Oscillograph of damped oscillation.
|From left to right
are shown the operator call box, Resonaphone receiver, change-over switch, and the pump handle key. The box on the wall contains the key relay.
The receiver will hear the repetition rate of the sparks.
|The also included a telegraph station to relay wireless messages.|
|The photo below shows an active amateur radio station located on the first floor of the Massie building.
The radio at the top left is a Swedish marine emergency quenched gap spark transmitter. In Scandanavia these spark rigs were legal into the nineteen sixties.
|The new AM bench assembled by Colin Leath, K11XU.
The following photographs are courtesy of Charles Arthur Moore.
For more information about the Museum please e-mail: Frederick Jaggi, President
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