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TTS 26B
Section 4
receiving mode of operation to the SEND switch.
The SEND switch will then establish the receive
connections a s follows in clockwise sequence:
a.
SEND
LOOP, REG B&G: The receive
m e t e r circuit i s directly connected to the
REC LOOP jack.
b.
SEND LOOP, REC LOOP: The battery
i s furnished through the m e t e r to the tip,
and ground i s extended to the ring of the
REC LOOP jack, requiring only an open
and closure of a d r y loop for a measurement.
c .
LINE (M =B&G, E =G&O): The m e t e r
circuit i s connected to the E jack and the
tip (E) of the LINE jack.
d.
DROP (M =B&O, E =G&O): The m e t e r
circuit i s connected to the ring (M) of the
DROP jack.
e.
LINE (M =B&O, E =G&O): The m e t e r
circuit i s connected to the E jack and tip
(E)
of the LINE jack.
f .
DROP
(M =B&O,
E
= G&O): The m e t e r
circuit i s connected to the ring
(M)
of the
DROP jack.
4.12 No connections a r e established between the
measuring circuit and the REC E&M jack when the
sending and receiving functions a r e combined in
the SEND switch.
4. 13
A description of the sending functions is
covered in the section devoted to the sending p a r t
of the set. A d i a g r a m showing the c i r c u i t connec-
tions which a r e established f o r the combined
sending and receiving operations
is
shown in
fig. 3 - 3 .
4. 14 The receiving c i r c u i t s a r e connected to the
measuring circuit through the
METER
CIRCUIT
switch a s follows:
a. In the
PPS
position a relay is inserted
in the external circuit; i t s contacts operate
a frequency measuring circuit.
In this
condition the m e t e r r e a d s pulses p e r sec-
ond (PPS).
b.
In the center position, marked
%
BREAK
DIRECT, the m e t e r is operated a s a
70
break m e t e r and connected directly to the
circuit under test.
c . In the
OJo
BREAK THRU
RELAY
position
the winding of a slave relay i s connected to
the receiving circuits and the m e t e r reads
the
70
break on the contacts of this slave
relay
.
4.15
SENDING
SECTION.
4 . 1 6 The sending section of the s e t provides the
means for generating signals which may be sent
on loop o r E & M c i r c u i t s . When the FUNCTION
switch
is
in the SEND
AND
REC position, the
TEST-SEND key switch selects the following
sources of signal:
a. In i t s normal position a continuous pulse
train controlled by an internal oscillator.
The frequency of this oscillator can be
controlled by the PULSES PER SEC switch.
b.
In i t s operated down position dial pulses
o r other signals generated in circuits con-
nected to the
EXT
DIAL jack.
In either c a s e the
70
break of the send signals
can be controlled by the ADJ
OJo
BREAK control,
and can be measured on the
% BREAK
s c a l e of
the meter incorporated in the set.
To check the
70
break of the transmitted signal, the FUNCTION
switch i s temporarily moved to the ADJ
%
BREAK
position.
4. 17 When the internal oscillator i s used, a
sine wave signal i s supplied to one winding of the
DRIVE relay.
When an external dial c i r c u i t is
used, signals having a wave shape approximating
the sine wave a r e supplied to this s a m e winding.
The other winding of this relay i s connected to a
DC circuit i n which positive o r negative bias can
be applied under the control of the
ADJ %
BREAK
potentiometer.
The
DC bias shifts the operating
point of the DRIVE r e l a y and causes i t to transmit
pulses which a r e lengthened o r shortened a s
compared to those transmitted in the absence of
any bias.
4.
18
In the biasing c i r c u i t described above, the
effective drive power of the relay becomes
unsymmetrical and appreciable amounts of
a r m a t u r e transfer time can occur.
Thus i t is
not desirable to d e r i v e the sending signals directly
f r o m the DRIVE relay. F o r this reason the.
contacts of the DRIVE relay a r e used to d r i v e a
second relay, the
SEND
relay.
This second
relay obtains full excitation whenever the DRIVE
relay operates.
As a r e s u l t of the bi-stable
c h a r a c t e r i s t i c s of the
SEND
relay, assisted by
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