Single Tone Interference Test

TM 11-5895-1012-10

testing except the local station acts as both trans-

(c) Remove the input signal by disconnecting

mitter and receiver in both input and output tests.

Transmission Test Set No. 1 and observe Transmission

Test Set NO. 2 voltmeter. If the voltage measured by

6-9. Single Tone Interference Test

Transmission Test Set NO. 2 does not drop in value

a. Purpose. This test will measure maximum single

when the input signal is disconnected, then the line

tone interference of circuits between stations or

noise is probably mashing the reading Of V2. This con-

within a station and determine circuit compliance with

&ion must be corrected before the test can be com-

the standard operating requirements. These inter-

pleted.

ferring tones may come from carrier leak or from

(d) If the voltage measured by Transmission

nearby equipment or systems.

Test Set NO. 2 (V2) did drop in value when the input

b. Test Equipment. Test equipment required to per-

signal was disconnected then calculate the Longi-

form this test consists of a Frequency Selective Volt

tudinal Balance using the following formula:

meter and terminating plugs (600 ohms) and patch

Longitudinal Balance (db) = 20 Log10V1/V2.

cords.

(4) Performance Standard. Minimum Longitu-

c. Station-to-Station Test. Contact the distant sta-

dinal Balance is 40 db.

tion and arrange for one station to act as transmitter

d. Station-to-Station Output Test. Contact distant

and one as receiver. Perform the procedure below and

station and arrange for one station to act as trans-

then reverse roles and repeat the procedure.

mitter and one as receiver. Perform the procedure

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

below and then reverse roles and repeat the procedure.

act as transmitter, prepare the transmitting circuit

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

shown in figure 6-7.

act as transmitter, prepare the transmitting circuit

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

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

as receiver, prepare the receiving circuit shown in

(a) Transmission test set jumpered as shown in

figure 6-7 and set the frequency selective voltmeter as

figure 6-6 with voltmeter function switch to on.

follows:

(b) Patch panel impedance selectors at 600

(a) Input impedance set for 600 ohms.

ohms.

(b) Input attenuator set so that the maximum

(c) Patch panel frequency selector at less than 5

level of the single tone interference is included in the

KHz.

measuring range of the voltmeter.

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

(3) Procedure.

as receiver, prepare the receiving circuit shown in

(a) Slowly sweep the frequency control of the

figure 6-6 and set the equipment as follows:

frequency selective voltmeter through the frequency

(a) Transmission test sets jumpered as shown in

range of the channel under test.

figure 6-6 with voltmeter function switches to on.

(b) Record the power level (in dbm) of the peaks

(b) Patch panel impedance selectors at 600

indicated by the frequency selective voltmeter. Con-

ohms.

vert this measurement to dbm0 by allowing for the

(c) Patch panel frequency selectors at less than

relative level of the transmission level point at which

5 KHz.

the measurement was made.

(3) Procedure.

(c) Convert this level from dbm0 to dbm0 us-

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

ing the conversion chart in figure 6-8. Read the fre-

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

quency of the interferring tone from the frequency

the top of the audio bandwidth (approximately 2700

selective voltmeter and then find the conversion factor

Hz). Adjust transmission Test Set No. 1 for a level of

for the frequency in figure 6-8. Then, dbrnc0 = dbm0

- 10 dbm0 as read at the receiving station on Trans-

+ conversion factor.

mission Test Set No. 3 voltmeter. Note this level and

(4) Performance Standard. Refer to the Technical

label it V1.

Services Schedules (table 4-2) for the maximum allow-

(b) Adjust the range control of Transmission

able noise for the channel being tested. The maximum

Test Set No. 2 for a suitable sensitivity and measure

single tone interference (measured in dbrnc0) will not

the voltage displayed on Transmission Test Set No. 2

exceed the level specified by the Technical Services

voltmeter. Note this voltage and label it V2.

Schedule.

(c) Calculate the longitudinal balance of the out-

d. In-Station Test. In-station testing is accom-

put circuit using the following formula:

plished in the same manner as station to station test-

Longitudinal Balance (db) = 20 Log10V1/V2.

ing except the local station acts as both transmitter

(4) Performance Standard. The permissable mini-

and receiver.

mum longitudinal balance is 40 db.

6-10. Impulse Noise Test

e In-Station Testing, In-station testing is ac-

a. Purpose. This test will measure impulse noise on

complished in the same manner as station to station

6-8