SECTION 3 TECHNICAL DESCRIPTION

TM 11-6625-3017-14

SECTION 3

TECHNICAL DESCRIPTION

This limited i. f. waveform is passed to the pulse

3.1 SYSTEM OPERATION

counter discriminator whose operation is illustrated in (c),

(d) and (e). A pulse of fixed amplitude and width is

General operation of the TF 2300A Modulation

generated every time the clipped i. f. signal passes

Meter can be explained with reference to the block

through zero in the positive-going sense as shown in (b)

schematic, Fig. 3-1.

and (c). At any given repetition frequency, these pulses

have a constant mean amplitude, Vm, provided the pulse

amplitude and width are fixed; thus when the p. r. f.

The r. f. input is heterodyned in the mixer with the

varies due to f. m. of the input, the mean amplitude will

local oscillator output, producing an intermediate

also vary directly as the modulation frequency. This is

frequency signal of 1.5 MHz. The output of the mixer is

illustrated in (c) and (d). In practice the limiter output is

fed to an i.f. Amplifier which has a linear

fed to a Schmitt trigger circuit, the resultant constant

phase/frequency response to f. m.

rise-time rectangular waveform being differentiated and

used to drive a pulse generator. The pulses from here

are later passed through a low-pass filter to remove all

From the i. f. amplifier, the signal can be passed

but the modulation frequency components.

through the f. m. or the a. m. sections, depending on the

positioning of the Function switch.

The l. f. signal (e) is then amplified in the 1st l. f.

amplifier, the gain of which can be standardized by the

SET CAL-F. M. front panel preset in conjunction with the

F.M. sections

calibrator, and passed through the 200 kHz low-pass

filter and, if required, to restrict the bandwidth to the

From the i. f. amplifier, f. m. signals, as illustrated in

audio range, through the 15 kHz low-pass filter.

Fig. 3-2 (a), are passed through three limiting stages to

eliminate all amplitude changes and produce a

rectangular waveform as shown in (b).

Fig. 3-1. Block schematic diagram.

3-1