Shunt Method of Calibration Using Incoming Rf Signal

plug (at the rear of the tuning unit)

a. Sign a 1 Pickup Device. T h i s b l o c k

d i a g r a m shows one of the three dipole

a n d mating jack J701 (on the in-

antennas connected, through the balanced-

t e r i o r wall of the main unit). The

t o - u n b a l a n c e d transformer (balun) and the

output signal drives audio amplifier

r e d color-coded rf cable, to the SIGNAL

V701 in the main unit. The ampli-

INPUT jack of the main unit. This color-

fied audio voltage produces an aural

coded rf cable is part of Electrical Cable

indication of modulated signals

A s s e m b l y Set MX-3410/URM-85. A sepa-

when one or two headsets are

rate and distinct dipole antenna is used to

p l u g g e d into PHONES jacks J702

c o v e r the full operating frequency ranges

and J703, respectively, on the main

of tuning units 2, 3, or 4. When tuning unit

unit front panel.

1 is in operation, either the loop or vertical

(2) Meter. The meter indication is de-

antenna must be used, and the test set is

r i v e d from meter detector V2 and

c a l i b r a t e d by the series method (para 5).

e l e c t r o m e t e r s V3-V4. The output

The other signal pickup devices which re-

f r o m electrometer V3 is coupled

quire shunt calibration of the meter depend

t h r o u g h terminal 8 of the tuning

on the method of coupling the signal to the

u n i t plug and the corresponding

input of the test set. They are used as de-

terminal of main unit jack J701 to

s c r i b e d below:

cathode follower V702 .4. The output

f r o m electrometer V4 is coupled

(1) F o r conductive measurements, the

t h r o u g h terminal 11 of the tuning

i n p u t from power or audio-signal

u n i t plug and the corresponding

lines under test is connected to the

terminal of main unit jack J701 to

t e s t set by special coupling net-

cathode follower V702B. These two

w o r k s . The following minor com-

c a t h o d e followers, t o g e t h e r with

p o n e n t s are used for conductive

m e t e r M701, make a bridge-type

measurements:

v a c u u m - t u b e voltmeter. The meter

employes a logarithmic 0- to 100-

Minor component

Nominal line

Frequency

m i c r o a m p e r e movement, and has

(common name)

impedance

range

two scales. One scale is calibrated

from -6 to +20-db; the second scale

50-ohm conductive cou- 50-150 ohms

150 kc to 30 mc

pler for tuning unit 1.

i s calibrated from 0 to 10 micro-

500-ohm conductive

150-500 ohms

150 kc to 30 mc

volt 1

coupler for tuning

f. Power Supply. The power supply pro-

Unit l.

50-ohm conductive cou- 50-150 ohms

20 to l,000 mc

vides seven different outputs for the

pler for tuning units

various circuits of the test set (fig. 1). The

2, 3, and 4.

i n p u t voltage required at the front-panel

500-ohm conductive

150-500 ohms

20 to 1,000 mc

coupler for tuning

POWER receptacle J721 is 115 volts, 50-

units 2, 3, and 4.

t o 400-cps. A complete block diagram of

the power supply is shown in figure 5.

(2) For pinpointing the source of rf

4. Shunt Method of Calibration Using

n o i s e interference from an instru-

Incoming Rf Signal

ment u h d e r test, the inductive

(fig. 2)

m e t h o d of coupling is used. The

f o l l o w i n g minor components are

Figure 2 is a block diagram which shows

d e t a i l e d operation of the equipment after

u s e d for inductive measurements:

the meter has been calibrated to produce a

full-scale deflection by using the output of

Minor component

Frequency

Characteristic

the impulse generator as a calibrating

(common name)

range

signal source. Setting the front-panel cali-

Magnetic field

Localizes magnetic field 150 kc-30

bration switch to the SERIES CAL& OPER-

components of rf energy

mc.

probe for

A T E position changes the circuit connec-

over the frequency

tuning unit 1.

range of tuning unit l.

tions from those described in paragraph 3.