On the Shunt Method for Measuring Reception Strength.

(Van der Pool. Philos. Mag. September 1917).

When measuring very weak currents in an antenna, one has to use a telephone shunted by a variable resistance; in this case, as the measure of the current strength one takes Hogan’s “audibility factor,”

\[ \frac{R+S}{S}, \]

where \(R\) is the resistance of the telephone, and \(S\) is the resistance of the shunt at which the signals disappear. Hogan (Electrician IX \(X_i\) p. 720, 1913) assumed that this quantity is approximately proportional to the square of the current strength \(J\) in the antenna.

Love (Philosophical Transactions vol. CCXV A p. 105, 1915), considering observations of the current strength in an antenna in long-distance telegraphy made by Hogan and Austin, found that they are in good agreement with the theoretical conclusions of Macdonald and Love, if it is assumed that

\[ \frac{R+S}{S} \]

is proportional to the current strength \(J\) for small values of it, and to \(J^2\) for large values.

In the article named in the title, van der Pool reports the results of his investigation of this question by laboratory means.

He used two circuits: in circuit I, representing the antenna, oscillations were excited; in circuit II, weakly coupled with I, a shunted telephone was included. The quantity

\[ \frac{R+S}{S} \]

was determined for various distances of circuit I from II, by which the same effect was obtained as if the current strength in antenna I were being varied. The magnitude of the current strength was not measured, but was calculated by the Maxwell–Rosa formula. The results confirmed Love’s assumption: for values of

\[ \frac{R+S}{S} \]

from 4 to 160,

\[ \frac{R+S}{S} \]

is proportional to \(J^2\).

for values from 1.2 to 4, \(\dfrac{R+S}{S}\) is proportional to \(J\). These conclusions are of considerable interest for measuring reception strength, since proportionality to the square of the current strength is usually assumed.

Gershunov.