Loose Coupler

© Brooke Clarke 2011

Secondary end & Switch	Primary end terminals marked: A        G S          S
Secondary Switch Wiring

In the early days of radio the loose coupler was commonly used to couple the antenna and ground system to the input to the receiver.  The early receivers used crude devices to rectify the radio frequency signal.  These rectifiers had impedance that varied a lot so some means of impedance transformation was needed.

The loose coupler is made up of two parts.  The primary coil is fixed to the frame and has a slider to vary it's inductance.  The secondary coil is mounted on two rods that are also electrical contacts.  The secondary coil can be moved relative to the primary coil changing the coupling.  The secondary coil also is tapped and the twelve position switch on the end of the secondary coil selects the tap allowing it's inductance to be varied.

The upper left terminal is marked A (Antenna) and the one to its right G (Ground).
The two lower left and right terminals are marked S (Secondary).

The A terminal goes to the end of the primary close to the terminal.  The G terminal goes to the slider above the primary.
The two S terminals go to the secondary support rods, but there doesn't seem to be a sliding contact, rather there are also wires connected to these terminals.
The right side S terminal is connected to the switch wiper.  I think the other S terminal is connected to the end of the secondary coil that's closest to the terminal.

A quick check with the Fluke 87 in Ohms mode shows there are problems with the switch contacts, some of them are open circuits. To make the needed repairs the unit will need to be opened.  Next is figuring out how to do that.

Pos	1	2	3	4	5	6	7	8	9	10	11	12
S-S Ohms	opn	18.6	35.4	interm	opn	27.0	31.2	opn	23.0	11.1	2.6	14.7

There is a single short wire coming up from the bottom of the secondary coil.  To that is soldered the wire that goes to the back of the switch. The opening is only a couple of inches so there's not enough room to get to the solder joints.

If you know the disassembly procedure, let me know.

Class Numbers

329 Demodulators
334 Tuners
336 Inductor Devices
343 Communications: Radio Wave Antennas

719005 Tuning Device for Wireless Telegraphy, W.S. Hogg, Jan 27 1903, -
848676 Electric Transformer, J. Murgas, Apr 2 1907,  -
877451 Means for Receiving Intelligence Communicated by Electric Waves, G.W. Pcikford, Jan 21 1908, - 329/347 926934 Wireless Telegraph Tuning Device, L. De Forest, Jul 6 1909, -
1042855 Interference Preventer for Wireless Telegraph Circuits, W.L. Walker, Oct 29 1912, 336/116 ; 336/129; 336/208; 336/45 -
1043272 Tuning Device for Wireless Telegraphy and Telephony, W.E.D. Stokes & G.W. Davis, Nov 5 1912,
1058555 Receiving Transformer for Wireless Telegraph Systems, E.L. Colby, Apr 8 1913, 336/116 ; 334/72; 336/129 -
1121479 Transformer, E.L. Colby, Dec 15 1914, 336/116 336/116 - series and/or parallel switching
1133441 Inductance Device for Wireless Electrical Signaling, C.O. Lorenz, Mar 30 1915, 336/116 ; 336/129; 336/231 - Conical coils
1497411 Transformer, J.C. Snell, Jun 10 1924, 336/45 ; 336/116; 336/129; 336/150; 74/502 - Concentric front panel knobs
1525563 Coil Mounting, L.J. Baker, Feb 10 1925, 336/129 ; 336/199 - Tripple wig-wag coils behind front panel
1528686 Tuning Unit of Radiophone Apparatus, J. Neumann, Mar 3 1925, 336/129 ; 336/116 - Loose Coupler behind front panel
1581366 Inductance Coil Control, G.A. Turner, Apr 10 1926,  336/129 - Tripple wig-wag coils behind front panel

Spark Museum - Loose Couplers -
Wireless Era Ham Gear and Commercial Wireless Equipment 1910 - 1927