Audio Frequency Test

TM 11-5895-1012-10

d. In-Station Test. I n - s t a t i o n t e s t i n g i s a c -

Table 6-1. Envelope Delay Measurements

complished in the same manner as station to station

testing except the local station acts as both trans-

mitter and receiver.

6-8. Minimum Longitudinal Balance Test

transmit and receive circuits and determine circuit

compliance with the standard operating requirements.

Any voltage that causes a current to flow in the same

direction in both conductors of a circuit is a

longitudinal voltage. This can be caused by extraneous

voltages induced into the circuit by either electro-

magnetic or capacitive coupling to both conductors

6-7. Audio Frequency Test

from other circuits, or as a result of any external

electrical disturbances. This test measures

a. Purpose. This test will measure maximum circuit

of the induced longitudinal voltage on the signal volt-

frequency change between stations or within a station

and determine compliance of circuits with the stand-

age by introducing a known signal voltage and measur-

ing the resulting longitudinal voltage.

ard operating requirements.

b. Test Equipment. The following test equipment is

b. Test Equipment. The following test equipment is

required to perform this test:

(1) Transmission Measuring Test Set (3 required).

(1) Noise Measuring Test Set.

(2) Transformer, 1:1 ratio, 600/600 ohm, audio,

(2) Frequency Counter (two required for in-station

center-tapped.

test).

(3) Resistors, 300 ohm 1%, 1 watt (2 required).

(3) Terminating plugs (600 ohms) and patch cords.

(4) Resistor, 150 ohm 1%. 1 watt.

c. Station-to-Station Teat. Contact distant station

and arrange for one station to act as transmitter and

(5) Terminating plugs (600 ohms) and

c. Station-to-Station Input Teat. Co

one as receiver. Perform the procedure below and then

station and arrange for one station to act as trans-

reverse roles and repeat the procedure.

(1) Transmitting Circuit. If the local station is to

mitter and one as receiver. Perform the procedure

act as transmitter, prepare the transmitting circuit

below and then reverse roles and repeat the procedure.

shown in figure 6-4 and set the equipment as follows:

(1) Transmitting Circuit. If the local station is to

(a) 1000 Hz Test Tone Source set for - 10 dbm0

act as transmitter, prepare the transmitting circuit

coupled to transmit line.

shown in figure 6-5 and set the equipment as fellows:

(b) Frequency Counter set to measure ac within

(a) Transmission test sets jumpered as shown in

.1 Hz

figure 6-5 with voltmeter function switch to on.

(2) Receiving Circuit. If the local station is to act

(b) Patch panel impedance selectors at 600

as receiver, prepare the receiving circuit shown in

ohms.

figure 6-4 and set the equipment as follows:

(c) Patch panel frequency selector at less than 5

(a) Frequency Counter set to measure ac within

KHz.

.1 Hz.

(2) Receiving Circuit. If the local station is to act

(b) Noise Measuring Test Set set Hi Pass filter-

as receiver, prepare the receiving circuit shown in

ing and 600 ohm input.

figure 6-5.

(3) Procedure. The transmitting station will

(3) Procedure.

measure the Test Tone Source and record the

(a) At the transmitting station, set the fre-

indication to the nearest .1 Hz. The receiving station

quency of the Transmission Test Set No. 1 to a value

will measure and record the level meter indication on

near the top of the

the Noise Measuring Test Set. The receiving station

2700 Hz). Adjust the

will then observe the indication on the Frequency

Set No. 1 for an inpu

Meter for one minute and record this measurement.

mit input as read on Transmission Teat Set No. 3 volt-

The two stations will then compare the recorded fre-

meter. Note the level in volts and label this V1.

quencies and determine the difference between them.

(b) Adjust the range control of

(4) Performance Standard. The maximum

Test Set No. 2 voltmeter for a suitable sensitivity,

permissible change between the transmitted and

measure the low longitudinal signal across the

received frequencies is 5 Hz.

ohm resistor. Note this level and label it V2.

6-6