level at the output of the amplifier. In this way, the equalizing

process will take into account line loss, equalizer loss, and

amplifier gain characteristic.

b. Circuit. An amplitude-frequency equalizer circuit (fig. 4-2) contains

two-basic circuits; one is for low-frequency, and the second is for high-

frequency equalization. The balance between the two circuits in the adjustment

process takes care of the frequencies which lie between the two limits; these

are called midfrequencies.

Figure 4-2.

Amplitude-frequency equalizer, simplified schematic diagram.

(1) Essentially, the equalizer circuit consists of a series-tuned

circuit (secondary winding of transformer A and capacitor C1) that

can be tuned to some frequency below the lowest line frequency. The

series-tuned circuit has little effect on the higher frequencies.

Resistor R1 adjusts the circuit Q, thus broadening the response as

needed.

Further, the low impedance of the tuned circuit near

resonance tends to pass the low frequencies more readily than high

frequencies, thus causing greater loss (dissipation) in resistors R1

and R2.

(2) A parallel-tuned circuit consisting of L1 and C2 is adjusted to

resonate at some frequency above the highest line frequency.

The

tuned circuit will therefore present highest impedance at the top

frequencies, but has little effect at the low frequencies. Resistor

R2 serves to lower the Q to the degree necessary to broaden the

response curve. The overlap of the broadened curves of both tuned

circuits determines the loss at midfrequencies.

(3) The combination of all adjustable elements in the equalizer produces

a variable-loss bandpass filter having cutoff frequencies below the

lowest frequency passed and above the highest frequency passed.