RTS TWI222 User manual

TECHNICAL MANUAL
TM3600 1 OIN 9300-360040
I MODEL TW1222 1 ~~12241
Including
TW1222-T
TW1222-CM
TWI-SK7O-DCU
TW IntercomSystem
Interface Units
RTS SYSTEMS
A Telex Communications Product

TECHNICAL MANUAL
ModelTWI224 /TWI222 InterfaceUnits
PROPRIETARYNOTICE
The information and design disclosed herein were
originated by and are the property of RTS Systems.
RTS Systems reserves
all patent, proprietary design,
manufacturing, reproduction, use an sales rights
thereto, and to any article disclosedtherein, exceptto
the extent rightsareexpresslygrantedtoothers.
COPYRIGHTNOTICE
Copyright 1988
by RTS Systems,Burbank, California,
USA.
ALI rightsreserved. Reproduction inwhole or
in part withoutwritten permission from RTS Systems
is prohibted.
UNPACKING INFORMATION
AND INSPECTION
Immediatelyupon receipt of the equipment,inspect
the shipping containerand the contents carefullyfor
any discrepancies or damage. Should therebe any,
notify the freightcompanyand the dealerat once.
The shippingModel
TWI224 / TWI222container
should
contain the followingcomponents:
OrderingNumber 9000-2195-00
-- TWI224
OrderingNumber 9000-2184-00
-- TWI222
RTS Systems
a Part Number Descriotion
9010-2195-00 ModelTWI224
9010-2184-00 Model TWI222
9300-3600-00 TechnicalManual
PrintingHistory:
6
FirstEdition: July 1980
SecondEdition: July 1989
This manual
is publishedby the Engineering
Department of RTS Systems,whieh is responsiblefor
its contents.
Written by: Daniel
F. Register
Editedby: SherylD. Thompson
Address
all communicationregarding this publication
to:
Directorof Engineering
RTS Systems
1100West Chestnut Street
Burbank,
CA 91506USA
RTS Systems
Burbank, CA 91506 / FSCM: 60572 TM3600 / SecondEdition, July 1989
Page
ii

TECHNICAL MANUAL
Model TWI224 / TWI222 Interface Units
TABLE OF CONTENTS
..
UnpackingInformation ............................................................................................................................................. n
...
Table Of Contents .......- ......................................................................................................................................... m
warranty ....................... "...,., ........... -......---.- "."--"-.."." .-.................. " .................................................... " ..... " .... v
ShippingInformation ......... ........................................................................................................................................... v
SECTION 1: INTRODUCTION AND SPECIFICATlONS
1.1 Introduction ........................................................................... ................................................................ 1-1
U Application Guide .............................................................................................................................. 1-1
13 Spedbtiions ........................................................................................................................................ 1-1
SECTION 2: INSTALLATION
Ref.No Ti&
21
RTS TO 4-Wue Cameras and Intercoms ............................................................................................... 2-1
22
RTS To2-Wue Systems ................................................................................................................... 22
23
RTSTo 2-Wm Telephone Wetpry ............................... I .................................................................... 2-3
2.4 RTS To
RCAPaven Systems ........................................................................................................... 2-5
sEClTON3: OPERATING INSTRUCTIONS
' 1
3.1 Introduction
..................................................... " ........................................................................................... 3-1
3.2 RTS To4-Wue SystemsOperation
........................................................................................................ 3-1
3.3
RTS To2-WireSystemOperation .................................................................... . ................................. 3-1
3.4 RTS To2-Wire TelephoneOperation..
.................................................................................................. 3-1
SECI'ION
4: TBEORY OFOPERATION
Ref. No Title
4.1 Introduction
................................................................................... ......................................... 4-1
4.2 FuuctidDwcription .............................. .............................................................................................. 4-1
4.3 TWI-222 Block Description ................................................................................................................... 4-2
4.4
Circuit Description .................................................................................................................................... 4-2
RTS Systems Burbank,
CA 91M6 / FSCM: 6057% TM36GU / SecondEdition, July 1989
Page iii

TECHNICAL MANUAL
Model TwI22a / Twrm Interface Units
SECTION 5: MAINTENANCE
Ref. No Title
5.1
Chaghg Impedance ......................................... ........................................................................................ 5-1
SECTION 6. LISTS OF REPLACEABLE PARTS
Ref. No Title
Introduction
.................................. ........................................................................................................ 6-1
How To ObtainParts ...................................................................................................................... 6-1
Shipping Lists ........................................... " .............................. ............................................................... 61
Fi Assembly ........................................................................................................................................ 6-1
Back Panelmbly ............................... " ............................................................................. ..................... 6-2
Front PanelAssembly ............................................................................................................................... 6-2
. .
Printed CuautAssembly .............................................................................................................................. 6-2
Fd Assembly,Model TWUZZ ......................... " ................................................................................... 6-4
S-ON 7: DIAGRAMS
Document
Number
SchematicDiagram, Interuun Interface TWI220 ................. - .............................. ....................... 7-2
Assembly Diagram, P.C.B. TWU24 InterfaceLayout .................................................................. 7-3
Assembly Diam, P.C.B. TWI224 Hold CircuitLayout ........................................................... 74
EngiaeeringNote, TWISK70DCU InterfaceCard ................................................................... 7-5
wkhg Diagram, TWISK70-DCU Interface ,, ...................................................... " ................... 7-6
TWI-SK70-DCU,
4-Wue InterfaceW/SAP 1024, sheet 1 of 2 ................................................... 7-7
sheet 2 of 2 ..... " ...... " ." ............................ " ...... ................................................................................. 7-8
SchematicDiagram,TWISK70-DCU ............................................ " ........................................... 7-9
Assembly Diagram, TWI-SK7DDCU Layout Chart ........................ " ........................................ 7-10
TWI-SKnrDCU,Squelch
CircuitPiggyback Board Installation to Interface Card .............. 7-11
sheet 2 of 2 ...... " .............................................................................................................................. 7-l2
TWISKMDCU Squelch Card, CircuitDescriptionsheet 1 of 2 ............................................. 7-I3
sheet 2 of 2 ........................................ .." .... ".... .. .............................................................................. 7-14
Schematic Diagram, SquelchMod For TWI-SK70-DCU .......................................................... 7-l5
Assembly Dim, P.C.B. SquelchM&cation For TWISK70-DCU Layout ................... 7-16
SchematicDiam, IntercomInterface TwI22a ....................................................................... 7-17
RTS Systems Burbank, CA 91M6 / FSCM: 60572 TM3600 / Second Edition, July 1989
Page iv

TECHNICAL MANUAL
Model
TWU24 / TWI222 InterfaceUnits
RTS
SYSTEMS' LIMITED WARRANTY
RETURN SHIPPING INSTRUCTIONS
The produds of RTS Systems, , a California ProcedureForRehuns:
corporation,are warranted to be
Free from defects in
materials and workmanship for a
period of one year
If repair is neeeasary, contact the dealer where this
from the date of sale. unit
was purchased
RTS Systems'
sole obligation during the warranty
period a to provide, without charge, parts and labor
neees~aryto remedy mvered defects appearing in
produds returned prepaid to RTS Systems,
1100 W.
Chestnut Street, Burbank, CaliFomb, 91U)6, USA.
This warranty doas not mver any defect, malfunction
orfailure
cad beyond the control of RTS Systems,
includingumeasonab1e or negligent operation, abuse,
accident, failuretofollow
instructions in this Manual,
defective
or improperassociated equipment, attempts
at moditidon and repair not authorized by RTS
Systems, and shipping
damage. Products with their
serial numbers removed or effaced arenot awered by
this warranty.
To obtain warrauty
service, follow the pdures
entitled "PROCEDURE FOR
RETURNS" and
THIPPING TO MAN~A~FOR~REP~~-
OR ADJUSTMENTlisted below.
This warranty is the sole and exclusive
warrantygiven with respecttoRTS Systems' pr 3'- ucts.
It
is the responsibilityof the user todeterminebefore
purchase
that this product is suitable for the user's
intended
purpose.
ANY AND ALL IMPLID WARRANTIES,
INCLUDING THE IMPLIED WARRANTY OF
MERClUNTABlLlTY ARE LIMITED TO THE
DURATION OF THIS EXPRESS LI~~ED
WARRANTY.
NEITHER RTS SYSTEMS NOR TEE DEALER
WHO SELIS
RTS SYSTEMS' PRODUCTS IS
LIABLE FOR INCIDENTAL OR
CONSEQUENTIALDAMAGES OF
ANY IUND.
IF repair through the dealer is not possible, phone the
RTS Systems Customer Service Department, located
at the factory,
as directed below. They will issue a
ReturnAuthorization Number
DO NOT RETURN ANY EOWIPMENT TO THE
FACIY)RY WITHOUT FIRST OBTAINING A
RElURN AUTHORIZATION NUMBER,
Be prepared to provide your wmpany's name,
address, phonenumber, a person tocontact regarding
the repair, the
type and quantity of equipment, a
descriptionof
the defect, and the serial number(s).
oUwtio11~regarding returns for repair should be
directed to: Customer ServiceDepartment
RTS Systems,
1100 W. Chestnut St.
Burbank,
CA 91506, USA
Telephone:
(818) 8407311
Telex: 194855
TeletaX [phone]
SHIPPINGTO MANUFACIVRERFOR REPAIR
ORADJUSTMENT
All shipments of RTS Systems, equipment should be
p& via United ParcelServiceor thebest available
shpper. The equipment should be shipped
in the
originalpacldngcartoa;
if that is not available, use any
suitablecontainer
that is rigid and of adequate size. If
a substitute container is used, the equipment should
be wrapped in paper and surrounded with at least
four inches of excelsior or
similar shock-absorbing
material.
All shipments should be directed to the
attention of the Customer Service Department and
must includethe ReturnAuthorizationNumber.
Upon com letion of repairs equipment
will be
shipper.
S returned
via United ParcelServiceor specified
RTS SystemsBurbank
CA 91506 / FSCM: 60572 Th9600 /Second Edition,July 1989
page v

TECHNICALMANUAL
Model TWI224 / TWI222 Interface Units
SECTION 1: INTRODUCTION AND
SPECIFICATIONS
The TWU22 and TWIZL4 series of interfaces are
designed to interface RTS Systems'
"TW" system to
other interwms. These interfaces derive operating
power from the RTS line, and are transformer
isolated to prevent ground loop interference.
Three
package styles are available - a wmpact portable
style
similar toour belt packs, a rack-mount style, and
a wnsole mount package. The rack mount version
may be ordered
with up to three interfaces in one
panel
13 APPLICATIONGUIDE
This section is intended to help you select the wneet
interfaceforyour application.
TWI222 to be
used with a line impedance ranging
from
25 ohmsto 1600 ohms.
The TWI222-CM is designed to interface an RTS
"TW" system directly to an RCA/DAVEN type
ca~bon mimophone intercom system, with an
impedance of
4-16 ohms (30 to 7 stations). To
determine the adimpedance of your system,
divide
120 by the number of stations on the line. For
example,
120 divided by 11 stations yields a line
impedanceof
10.9 ohms.
The TWI222-T is
designed to interface an RTS
system to a 2-wire wet telephone line. It includes an
electronichold circuit.
The TWU22 interface is for interfacing an RTS
system to a four wire intuwm system.
This would 13 SPECIFICATIONS
include some teldon broadcast cameras, the
MeCurdy interwm systems, radiotelephones, and
Typ'ncal Gain: 14 to 20 dB eachdirection
cameras
which have waxial or trkial cable adapters Balance
Null Capabiity 20 dB
(except for
the Hitachi SK-70 with DCU). If your Input/Output Voltages: -30 dBm to
+10 dBm
camera
has the option of operatingin either fourwire Biiteral Current Sources
or two wire mode,
use the four wire mode and our Peak Current Drive.
10 mA (200 ohms)
TWI222interface.
This will result in easier set up and
betterperformance..
The TWU22 may also be used to
interface
to a Carbon Mic system through a TIP-
RING-SLEEVE jack on the Carbon Mic system,
however better performance
will be achieved using a
TWI222-CM connected directly to the Carbon Mic
system's line.
Two TWI222's can be used tointerface
2RTSTW"systemsover2telwdrypairs. Thisis
prefered to
using 2 TWI222-Ts over telephone lines.
The TWI222 interfaces are for interfacing an RTS
system to other
two wire intercom systems. The
TWU22 is supplied in three different wnIigurations,
the
TWI222, theTWI222-CM, and the TWI222-T.
The TWU22 is designed to interface RTS 7%'"
systemsto interwm systems with a line impedanceof
200 ohms nominal, with a range of 100 to 400 ohms.
The impedancemay be user selected,allowing the
RTS SystemsBurbank,
CA 91506 / ESCM. 60572 Th9600 / SewndEdition, July 1989
Page 1-1

TECHNICALMANUAL
Model TWI22A / TWI222 Interface Units
SECI'ION 2: INSTALLATION
2.1 RTS TO &WIRE WLMERAS AND INTERCOMS
Turn d gain and balance cont~oIsto minimum. Connect the RTS lineto the RTS LINE jack on the rear of the
TWI-224. Conneb the Listenbus of the 4-wire system to pins 1 and 2 of the +pin frontpanel XLR onthe TWI-
224.
Coaned the talk bus of the 4-wire systemtopins 3 and 4 of the 4-pin front-panel XLR as shown in figure
2-1. This talk busmust present a 100 ohm to 400 ohm impedance tothe outputof the TWI-224. If it doesnot,
terminate the
TWI-224 4-wire outputwith a 200 ohm 114 watt resistor.
4 WIRE IN LO
TO TALK BUS
FROM LISTEN BUS
-
FOR W1224-RM(E) UNITS USE A4F (FEMALE) CONNECTOR
Fire 2.1
ConnectorAnd Cable Wiring ForThe TWI-224
RTS SystemsBurbank, CA 915061 FSCM 60572 TWWO/ Second Editioq July 1989
Page 2-1

TECHNICALMANUAL
Model lWE24 / TWI222 Interface Units
22 RTS TO 2-WIRE SYSTEMS
First cobthat the external intercomsystem has anominal impedanceof 2QO ohms (100 to 400 actual). If it
does not, see section 55 on how to changethe impedance of the TWI-222.
Turn all gain and balanfficontrols to minimum. Connect the RTSline to the RTS LINE jack on the rear of the
TWI-222. Conned the external intercomlinetopins 3 and 4 of the front-panel XLR-4 wnnector. See figure 2-
2. This input is capacitor coupledand can withstand dc line voltage-s as high as 25 volts
FOR TW1222-RM(E) USE A4F (FEMALE) CONNECTOR
4
< 3
2
: 1
-
Figure 23
Connector And Cable Wiring For The TWI-222
HI
2 WIRE IN/OUT LO
N/C
RTS Systems Burbank, CA 915061 FSCM: 60572 TM3600/ Second Edition, July 1989
Page 2-2

TECHNICAL MANUAL
Model TWI224 / TWI222 Interface Units
23 RTS TO 2-WIRE TELEPHONE WET/DRY
Turn all gain andbalance controlsto minimum, switch tebholdswitchoE Connedthe RTS lineto the RTS
LJNE jack on the rear of the TWI-222T. Connectthe telephone linetopins 3 and 4 of the front-panel XLR-4
~~nnedor. Polarity is not important. Seefigure 2-3. This input is capacitor coupledand can withstandvoltages
as high as M volts.
Onrack mount interfaces
(lWI-222T-RM), the rear panel stereophonejack is connectedin parallel with the
front-pel
XLR-4. Thus the tip and ring of the rear phonejack may be used instead of the front XLR-4 jack.
See figure 2-4. Do not use both jacks at the same time.
I
i
I
I
I
I
I
I
I
I
I
I
I
FOR TW1222-T-RM(E) USE A4F (FEMALE) CONNECTOR
I
I
I
I
I
I
-
4 TIP
< 3 2 WIRE IN/OUT RING
< 2
< 1 N/C
TO TELEPHONE
LINE
Fire 23
ConnectorAnd Cable Wiriag ForThe TWI-222-T
RTS SystemsBurbank, CA 915061 FSCM: 60572 TMbCQ/ Second Edition, July 1989
Page
2-3

TECHNICAL MANUAL
Model lWI224 / TWI222 Interface Units
TO
TO TELEPKNJE
TWI-222-
T-RM - RI
REAR
PANZL
Figure 2-4
Connector And Cable Wi For The TWI-m-T-RM
RTS SystemsBurbank, CA 91506/ FSCM: 60572 Th9600/ Second Edition, July 1989
Page 2-4

TECHNICAL MANUAL
Model TWI224 / TWI222 InterfaceUnits
2A RTS TO RCA/DAVEN SYSTEMS
The
TWI-224 may be wnnectedto a Carbon Mic systemthroughone of its user station's TIP-RING-SLEEVE
jacks. Usethecableshown in figure 25. Turn gain andbalance controls tominimum.
There
are disadvantagesto this method. Thereturn signal from the carbon mic system can notbe nulled out
resulting in excesiw sidetoneon both systems. This is usually suitablefor a small number of stations(less
than
7).
TO TIP - RING -SLEEVE
JACK ON CARBON
MIC SYSTEM
TO XLR-4
ON TWI-224
SWITCHCRAFT SWITCHCRAFT PLUG
A4-M ~0~~~8267, # 482,
#483 or PJ-0518
Figure 25
AdapterCableXAC 244-1
ToWMed a TWI-22Z-CM toa Carbon Mk Sysrem, connect theRTS linetotheRTS LINE wmector on the
rear panel of the TWI-222-CM. Connect the line of the Carbon Mic systemtopins 3 and 4 of thefront-panel
XLR-4 conneetor. Seefigure 2-2
RTS SystemsBurbank, CA 9W/ FSCM: 605'72 TM3MX) / SecondEdition, July 1989
Page 2-5

TECHNICAL MANUAL
Model TWU24 / TWI222 InterfaceUnits
SECllON
3: OPERATING INSTRUCTIONS
3.1 INTRODUCTION
After making connections as desaiiin section
2
Speak or hum into the carbon microphone headset
the unit
is ready to be adjusted.
This section and adjust the BALANCE FROM RTS control until
describes how to adjust and operate each of the a null
is obtained.
installations dadbed in don 2
4 after the
system is adjusted, any part of the system changes, Decrease the GAIN FROM RTS control to
readjustment may
be required. minimum.
32 RTS TO 4-WIRE SYSTEMS OPERATION Use an RTSuser stationto listen on the RTS system.
Turn the microphoneoff andvolumetomaximum.
After makingthe donsdescribedin don
2%
set all GAINand BALANCEcontrols on the TWU24
Increasethe GAIN TORTS tomaximum.
to minimum.
Turn power to the RTS and the 4-wire
system on Establishthat both systems are operating Adjust the BALANCE TO RTS control for a null in
properly.
the noise asheard on theRTS system.
Plug a carbon miaophone headset into
the CARBON
MICONLYjack locatedonthe rear panel.
Increasethe GAIN FROM RTSto
50%.
Hum into the carbon miaophone and adjust
BALANCE FROM RTS until
the. best null is
obtained.
With one person on the RTS "rW" line and another
on the &wire system, adjst the GAIN controls
until
both people can hear each other clearly.
33 RTS TO 2-WIRE SYSTEM OPERATION
After making
the comeetionsdesaidin sectinn 22
se3 all GAINand BALANCE controls on the TWI222
tominimum. Turn on the power to the RTS and the
Zwire system.
Con6nn that both systems are
operatingproperly.
Plug a carbon miaophone headset into the
CARBON-MIC-ONLY jaek on the
rear of the
TWI222.
Set the BALANCE FROM RTS control to
approximately 50%.
Reduce the GAINTORTS to minimum.
The interface is now balanced and care should be
taken not to disturb the balance controls. An
improperlybalancedinterfacemay oscillate.
Setboth
gain controlstoapproximately 25%.
Have two people establish two-way communication
through the interfaec; adjust the gains so that each
person
can be heardclearly.
3.4 RTS TO 2-WIRE TELEPHONE OPERATION
After making the wnnectionsdescribed in section 23,
turn the TEE0HOLD switch off and all level and
gain controls to minimum. Turn power to the RTS
system onandverify that the systemworks.
Plug a carbon miaophone headset intothe CARBON
MIC ONLY jack on the rear of the TWIlU-T. On
rack mount versions ('IWKZI-T-RM)
the carbon mic
jack
is onthe frontpanet
Set the BALANCE FROM RTS control to
approximately
50%.
Increase the GAINFROM RTS controltomaximum.
Inaeasethe GAIN FROM RTS controlto maximum.
RTS SystemsBurbad,
CA 91506 / FSCM: 60572 TM3600 / Seeond Edition,July 1989
Page 3-1

TECHNlCAL MANUAL
Model TWIZ24 / TWU22 Interface Units
Speak or hum into the carbon microphone headset
and adjust the
BALANCE FROM RTS control until
a null is obtained.
Decrease the
GAIN FROM RTS control to
minimum.
Use an RTSuser stationtolisten on the RTS system.
Turn the microphoneoff and volume to maximum.
Increasethe
GAIN TO RTS tomaximum.
Adjust the BALANCE TO RTS control for a null in
the noise
as heard on the RTS system.
Reduce the GAIN
TO RTS tominimum.
The interface is now balaaced and care ahodd be
taken not to disturb the balance wntrok. An
improperlybalanced interface may odate.
Set both
gain controlsto approxhately 25%.
Have two people establish two-way wmmunication
through
the interface; adjust the gains so that each
person
can be heard dearly.
RTS SystemsBurbank, CA 91M6 / FSCM: 60.572
Seaond Edition, July 1989
Page 3-2

TECHNICAL MANUAL
Model TWI224 / TWI222 Interface Units
SECTION 4: THEORY OF OPERATION
4.1 INTRODUCTION
Section 4 desenihow the TWI224 works. Section 42 desuibesthe circuit as used in both the Weand 2-
wire models. Sedon 43 describes the TelcoHold circuit which is used in theTWI222-Tand TWI222-T-RM.
43 FUNCTIONALDm-ON
Figure 4-1 shows the block diagram of the TWI224. The RTS "ZW" intercom comects to the XLR-3-31
eonnebm at thelower lett
LML
5mAfiOLT 'A
XLR-4-31
CURRENT SOURCE
RING
LEVEL
GAIN TO
RTS
XLR-3-31 CURRENT SOURCE
RTS
YiE
IN RACK MOUNT (-RM) (E) VERSIONS. CONNECTOR 1s
AN XLR-4-32 (MALE).
Figure 4-1
TWI224 Block Diagram
RTS Systems Burbank, CA 9U06 / WCM: 60572 Th9600 / SecondEdition, July 1989
Page 4-1

TECHNICAL MANUAL
Model TWI224 / TWIZ22 Interface Units
Power to operate the intertace is derived from
channel
1. Audio from either channel 1 or 2 of the
RTS interwm passes through the channel select
switch to
the output of a biieralcurrent source. The
bilateral current source presents a
high input
impedanceto
the RTS line. Si is picked off of the
balancepot
and sent to the LEVELFROM RTS pot.
This control sets the levelgoing to the external 4-wire
system.
Next an ic provides 20 dB of gain. This signal feeds
the input of
another biikteral current source. The
output passes through a
1:l transformer to the talk
bus of the external4-Wire system. The output of this
current source must be terminated with 100 to 400
ohms. If the externalinterwm does not present this
impedance to the 4-wire output, an external 200 ohm
resistormust
be used.
The 4-wire input of the front-panel -431
wnnedor passes through a 1:l transformer to the
LEVEL TO RTS pot. Theoutput of the pot feedsan
ic amplifier with a gain of 20 dB. This feeds the
input of a bilateral current source. Output from the
current source
is inverted when compared to the
input. Oneend of the BAL4NCE controlwnnectsto
the input while the other end connectsto the output
Thus at some point in the middle of the pot the out-
of-phasc output
will cancel the input such that the
return to the &Wire system
is miaimizcd. Too much
return to the &Wire system would mean too much
sidetone on the
4-wire system. The balance control
does not affectsidetoneon the RTS system.
Thetest headset wnnedor provides a wnvienentway
to balance the system. It
is wnneeted to tak and
listen to the RTS system, with a carbon-mic headset,
just
as if it were anotherstation on the 4-wire system.
43 lWEl2 BLOCK DESCRIPTION
Fwe4-2
is the block diagram for the TWI222 It is
similar to the he except there are two balance
wntrolsand only one transformer.
Power for the interface
is derived from channel 1 with
a specialregulatorcircuit.
Audio from RTS passes through the BALANCE
FROM RTS pot to the LEVEL FROM RTS pot.
The
signal is then amplitied 20 dB by an ic amplifier.
This feedsthe bilateral current source.
Output from the current source drives
the external2-
wire interwm through a kl transformer. This output
is inverted.
The BALANCE TO RTS wntrol wnneds to both
the input and
the inverted output. Near the center of
the pot
is a place where the out-of-phase signals will
cancel. It is importantto setthe balance wntrol for a
null or feedback will occur.
Input from the external 2-wire interwm enters the
TWIZZL through the front-panel XLR43L The
signal is picked off of the BALANCE TO RTS pot.
The LEVEL TO RTS pot sets the level going to the
RTS system.
20 dB of gain is provided by an i.c
ampli6er. Output from the amplifier feeds another
bilateral current source
which provides oulput to the
RTSline.
Again the balance wntrol must be set to null the
signal wming from
the external interwm system or
feedback oscillation
will result.
Thetest headset jack
is connectedtotalk and listen to
the RTS line
with a carbon-mic headset. Persons on
the external interwm
will not hear, nor will they be
abletospeak to, the person using the test headset.
4.4 CIRCUIT DESCRIFTION
This section describes the circuit operation of the
TWIZL4. Thepower supplyof the lWIZ4 derives its
power from channel 1 of the RTS line except forlocal
power
(LP) units which derive their power from a
wall-plugtransformer
with an outputof 14 volts dc.
CR2 provides reverse current protection while R30
acts as a fuse on severe overvoltage conditions or
catastrophicunit failure.
RTS SystemsBurbank,
CA 91506 / FSCM: 60572 TM36Ofl/ SewndEdition, July 1989
Page4-2

TECHNICALMANUAL
Model TW1224 / TWU22 Interface Units
LEVEL
WIN TO RTS
RTS
20db A
A
XLR-3-31
'4
CURRENT SOURCE
3
RTS -7
CHANNEL +12
SELECT 1
REGULATOR
+*
CONNECTOR
IN RACK MOUNT (-RM) (E) VERSIONS, CONNECTOR IS
AN XLR-4-32 (MALE).
Figure 4-2
TWU22 Block Diagram
RTS Systems Burbank, CA 91506 / FSCM. 60572 TM3600 / Secnnd Edition, July 1989
Page 4-3

TECHNICAL MANUAL
Model TWI224 / TWIm InterfaceUnits
4A CIRCUIT DESCRIPl'ION (continued)
VR2 proteds the unit from excessive line voltage by
shunting anything over 36 volts to ground. High
voltage spikes can occur when many user stations are
unplugged from the RTS line at once.
The output of U2
is set for U volts by R32 and R31.
U2 should read 12 volts between the adjust (A) and
output (0)
terminals.
C25 slows down the current response. of U2. This
keeps the input to U2 a high impedance so that it
does not "short out" the audio on
the RTS line. C26
provides filtering.
Q1
is a constant current source to VR1 which
provides
6 volts to bias the op amps. C28 provides
filtering.
Audio from the RTS intercom enters through the
rear-panel XLR-331 (lower left) and is decoupled by
C20 and (29. These capacitorsare largebecause hal£
of the capacitance.
is lost by their bipolar arangement.
C20 and C29 must also be large because they must
pass low frequencies. If they did not, the output level
of the bilateral current source would go up and
the
circuit would bceome unstable.
The
signal continuesthrough C19 to the output of the
bilateral current source at the right of R26. C19 is
largefor the same reason that C20 and C29 are large.
It
is there to block dc from channel belect switch SL
This eliminates clicks when switchingchannek.
The output of the bilateral current source presents a
high impedance to the incoming signal. This is
because a bilateral mntsoum converts a varying
voltage input to a varying current output. Hence
"current source". When the input voltage
is not
varying, ie. no input,
the output current will not vary.
In order for the output current to remain constant,
the circuit must follow the voltage variations
coming
in the output so that no current is drawn (0 volts in =
0volts out). Thus the circuit is actively following the
voltage coming in the output so that it is a high
impedanceand doesnot load the line.
The
signal continues through R23, C18 and RllB
through the wiper. RllA
(GAIN FROM RTS) sends
the signal through
C7 to U1. This part of U1 is an
amplifyingstage with a gain of 10(20 dB).
U1 is designed to operate with a bipolar power
supply. By biasing the inputs to
+6 volts, the i.c can
operate on _& single-ended + 12 volt supply. This
biasing is done by R10 and the 6 volt source.
Ulb
is another bilateral -nt source whose output
feeds the external intercom through
T2. For units
with the
-CM (carbon mic) option, T2 is replaced
with a 200:8 transformer. -T (Telco) units have T2
connected for k2stepup. CL is largein order to pass
lowfrequencies.
Audio from the
extemal intercom enters through T2
(upperright) to Ulb, the output of a bilateral current
source. From
the wiper of R25B (BALANCE TO
RTS) it
passes throd C30, jumps to point 18 1 where
it joins
RZSA (lower right). T1 is not used in the
TWI222. R29 and CU roll off low frequencies to
keepthe circuit stable.
Uld
has a gain of 10(20 dB). This feeds Ula which
is the current sourcethat feedsthe RTS line.
RTS SystemsBurbank,
CA 91506 / FSCM: 60572 TM36Ml /Second Edition, July 1989
Page 44

TECHNICAL MANUAL
Model TWllZQ / TWU22 Interface Units
SECTION 5: MAINTENANCE
5.1
CHANGING IMPEDANCE, APP NOTE DR-501 (see following application note)
RTS
Systems Burbank, CA 91M6 / FSCM: 60572 TMXXXX / Seumd Edition, July 1989
Page 5-1

Application Note
SUBJECT TWI-222 INTERFACE
& TWI-224 INTERFACE
APPLICATION: CHANGING IMPEDANCE
GENERAL INFORMATION
SPECIFIC DATA CUSTOMER:
DATE
2/5/80
APP NOTE F DR-101
PAGE 1 OF 2
The impedance of the TWI-224 may be changed tobetter match
your system. Normally, the TWI-224
is built to interface 200 ohms
at the input and 200 ohms at the output. The TWI-222
is built to
interface to a 200 ohm line. This may be changed to 50 ohms or 800
ohms nominal. In the 50 ohm mode, the interface
will handle 25 to
100 ohms.
In the 200 ohm mode, the unit will handle 100 to400 ohms.
When the interface
is set for 800 ohms, it will handle 400 to1600
ohms.
Should you find that your system
is some impedance other than
200 ohms, change the TWI-222 or TWI-224 tomatch your system. Find
the drawing that applies to the change you want tomake. Cut the
trace and add the jumper shown.
2
WIRE: 50 OHMS
4
WIRE: 50 OHMS OUTPUT FROM TWI-224
I
RTS Systems BurbqCA 91M6 / FSCM: 60572 TMXXXX / Second Edition, July 1989
Page 5-2

1100 Nest Chesrnul Streel Burbank Calrforn,a 91506 213 843-7022
Application Note
SUBJECT TWI-224 INTERFACE
APPLICATION CHANGING IMPEDANCE
GENERAL INFORMATION
SPECIFIC DATA CUSTOMER.
DATE
2/5/80
APP NOTE = DR-101
PAGE 2 OF 2
2 WIRE: 800 OHMS
4 WIRE: 800 OHMS OUTPUT FROM !LWI-224
RTS
Systems Burbank, CA 91506 / FSCM: 60572 TMXXXX / Second Edition, July 1989
Page 5-3