MIL-PRF-15305 Coils, Electrical, Fixed And Variable, Radio Frequency General Specification ForThis specification covers the general requirements for radio frequency coils, fixed and variable, for use as simple inductive elements in radio frequency circuits. Procurement of coils of a specific design will require additional data in the form of complementary Service documents, giving detail electrical and mechanical requirements, tolerances, and applicable additions and exceptions to the general requirements and tests specified herein \(see 3.1\).

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MIL-PRF-15305F

4.6.3 Winding continuity (see 3.6). All windings of coils shall be tested for electrical continuity by any suitable

means that will not introduce currents in excess of the rated value, or the incremental current value (when specified

(see 3.1), whichever is less.

The following test circuit is recommended for ferrite core coils to limit the test current to less than .6 mA.

4.6.4 Operating torque (see 3.7) (applicable only to variable coils). Coils shall be exposed to a temperature of 25�

C, with a tolerance of +10�C and -5�C. The coil under test shall be rigidly clamped by the body. The tuning core shall

be rotated for eight cycles (16 excursions) from maximum core extension to minimum position for one complete cycle

while not exceeding the maximum or minimum torque specified (see 3.1). Each cycle shall take a minimum of 40

seconds to perform.

4.6.5 Electrical characteristics (see 3.1 and 3.8). The coils shall be mounted by their normal mounting means on

their applicable test fixture. The electrical characteristics to be determined shall include inductance, Q, self-resonant

frequency, and dc resistance. Additional electrical characteristics shall be measured when specified (see 3.1).

4.6.5.1 Inductance. Unless otherwise specified (see 3.1), effective inductance of coils shall be measured at the

frequency specified. For cylindrical coils, the test procedures of 4.6.5.1.1 and 4.6.5.1.2 shall be used. For quality

conformance inspection, the measurement of effective inductance shall be referred to a comparison standard for

correlation, when specified. (see 3.1, 4.4.2.1, and 6.4). When true inductance is specified (see 3.1), the following test

procedure, or equivalent, shall be used. A calibrated capacitor shall be used to tune the winding to resonance at

several frequencies. The points shall describe a straight line of added capacitance, one point of which shall be 1/(fo) ,

as abscissa, versus the reciprocal of the frequency squared, as ordinate, to be plotted, and true inductance to be

calculated by the following formula:

True inductance = KM

= 0.0253

Where:

4š 2

M = Slope of the line representing added capacitance.

fo = Self-resonant frequency of the coil at the abscissa of zero capacity.

4.6.5.1.1 Effective inductance for cylindrical coils (inductance 0.10 to 10.0 microhenries inclusive). The tests shall

be performed using a Q meter such as Hewlett Packard (HP) models 260A, HP4342A, HP250RX meter or equivalent

at appropriate test frequencies as listed in the instructions for the test equipment. Suitable means shall be used to

calibrate the frequency dial of the Q meter within �0.1 percent for the applicable test frequency. Frequencies to be

used for testing the various ranges of inductance shall be as follows:

Inductance range, microhenry (�H)

Reference test frequency megahertz (MHz) for 260A

0.10 to 1.0 inclusive - - - - - - - - - - - - - - - - - - - - - - - -

25.0

Above 1.0 to 10.0 inclusive - - - - - - - - - - - - - - - - - - -

7.9

Allowance shall be made for the internal inductance of the Q meter and the test fixture as determined in 4.6.5.1.1.1.