GenRad 1491-D Decade Inductor

  • Most accurate decade inductor commercially available, accuracy's as good as 0.8%
  • Inductance range from 1 mH or 100 µH to 11 H
  • Shielded toroidal cores for small mutual inductance and minimal effect from external fields
  • Sealed against moisture for long-term stability
  • High-Q, 200 and above
Priced at
The GenRad 1491-D Decade Inductance Box is the most accurate decade inductor commercially available. The 1491-D has a max inductance of 11 H with a resolution of 1 mH.

The decade switch has high-quality ceramic stator and-rotor members and well-defined ball-and-socket detents. All contacts are made of a silver alloy and have positive wiping action. Shielded toroidal cores are used for small mutual inductance and minimum effect from external fields.

The 1491-D decade inductors are convenient elements for use in wave filters, equalizers, and turned circuits throughout the range of audio and low radio frequencies. As components in oscillators, analyzers, and similar equipment, they are especially useful during the preliminary design period, when the ability to vary circuit elements over relatively wide ranges is necessary to determine optimum operating values. The 1491-D Decade Inductors have values of low-frequency storage factor, Q, that are much larger than those of air-core coils.

GenRad 1491 Decade Inductor Basic Specifications (Full specifications can be found on datasheet)

1491D Decade inductor, 4 decades, 11.11 H total inductance, 1 mH per step 
1491G - Decade inductor, 5 decades, 11.111 H total inductance, 100 µH per step

Accuracy (Low Frequency, Low Signal Level):

Model  100 µH  1 mH  10 mH  100 mH  1 H 
1491-D N/A 2% 1.6% 0.8% 0.8%
1491-G 2% 2% 1.6% 0.8% 0.8%

Frequency Characteristics: Percentage increase in effective series inductance (above the zero-frequency value, Lo) may be obtained by interpolation in accompanying graph (see Figure 2 on datasheet or in manual) for any setting to the highest-value decade used, when LOW terminal is grounded to cabinet.

Zero Inductance: Approximately 1 μH

Maximum Voltage: 500V rms. Switch will break circuit at 500V if turned rapidly, but voltages above 150V may cause destructive arcing with switch between detent positions.