• Country
• Great Britain (UK)

• Manufacturer / Brand
• EMI; Hayes, Middlesex

• Year
• 1947 ??

• Category
• Radio part (not a module) 

• Radiomuseum.org ID
• 357040

Click on the schematic thumbnail to request the schematic as a free document.

• Wave bands
• Short Wave (SW only)

• Power type and voltage
• No Power needed

• Loudspeaker
• - - No sound reproduction output.

• Material
• Various materials

• from Radiomuseum.org
• Model: Variable Inductor Part of T.1509 Transmitter - EMI; Hayes, Middlesex

• Shape
• Miscellaneous shapes - described under notes.

• Dimensions (WHD)
• 3.5 x 3.5 x 13.5 inch / 89 x 89 x 343 mm

• Notes

• The RAF T.1509 shortwave transmitter employs variable "roller coaster" inductors in the oscillator (L200, L203), multiplier (L402) and power amplifier (L2) stages. The illustrations and schematic diagram show L402. The ceramic coil former is mounted on a shaft that is supported by ball bearings in each end plate of the frame, and rotated directly by a knob on the transmitter front panel via a flexible coupler. The knob has a plated brass dial engraved 0 to 100 over 360˚, and a gear mechanism operates a turns counter that is visible through a small magnifying lens. The inner knob of the concentric pair turns a screw which can lock the outer control knob in any position.

  As the coil former rotates, a 16.5 mm diameter grooved contact roller tracks the 35-turn winding as it slides up to 98 mm along a 4 mm diameter shaft. Springs at the pivots attached to each end of the shaft maintain the roller tightly pressed against the coil. Mechanical stops on the gear engage with a projecting screw on a bushing on the control shaft when the roller reaches either end of the coil. In L402, the unused section of winding is short-circuited in order to avoid the development of a high voltage across it when its electrical length is half the operating wavelength. As this configuration reduces the Q, it is not used for the oscillator coils L200 and L203, which are not at risk of corona discharge as they operate at low power. The coil, roller and associated mechanical parts are silver plated. 

• Mentioned in
• -- Original-techn. papers. (AP 2550B)

• Author
• Model page created by Bruce Taylor. See "Data change" for further contributors.

• Other Models

• Here you find 37 models, 27 with images and 17 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
  All listed radios etc. from EMI; Hayes, Middlesex