IRT VA-100NC User manual

I
IR T ElectronicsPty.Ltd. A.C.N. 000832575
26 Hotham Parade, ARTARMON. N.S.W. 2064 Australia
National: Phone: [phone]Fax: [phone]
International: [phone] [phone]
VA-100NC
VIDEODISTRIBUTIONAMPLIFIER
Telecom Serial 347 Item 55
802995
21-10-1991
DESIGNED AND MANUFACTURED
IN AUSTRALIA
IRT Communications
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VA-100NC
VIDEO DISTRIBUTION AMPLIFIER
INSTRUCTION BOOK
Serial 347 Item 55
Section Contents Page
1. General Description 3.
2. AccessoriesAvailable 4.
3. Technical Specifications 5.
4. CircuitDescription 6.
5. Installation 7.
6. Setting up Procedure 7.
7. Maintenance 8.
8. Table of Voltages 9.
9. CircuitDiagrams
10. PartsLists
WARNING
OPERATION OF ELECTRONICEQUIPMENTINVOLVES THEUSEOF VOLTAGES
AND CURRENTSWHICH MAYBE DANGEROUS TO HUMANLIFE.OPERATING
PERSONNELSHOULDOBSERVE ALL SAFETYREGULATIONS. DONOT CHANGE
COMPONENTS OR MAKEADJUSTMENTSINSIDE THE EQUIPMENTWITHPOWER ON
UNLESSPROPERPRECAUTIONS ARE OBSERVED. NOTETHATUNDERCERTAIN
CONDITIONSDANGEROUSPOTENTIALS MAY EXIST IN SOMECIRCUITSEVEN
THOUGHPOWERCONTROLS AREINTHEOFF POSITION.
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GENERAL DESCRIPTION
The VA-100NC isa B.C. poweredVideoDistributionAmplifier
of modularconstructionhavingfacilities for cable equalization,
longitudinal hum reduction and clamping.
The input is designed to provide a bridgingloopimpedance
over the videobandwidthwithrespect to75 ohm. Six75ohm D.C.
coupledoutputs are provided.
The input and outputgrounds are separated to allow for
rejection of longitudinallydevelopedhum.
Cableequalization is provided forupto300 metres of75ohm
videocable.
Front panel controls allow the videogain tobe varied bya
minimum of+/- 3dB, andthe cableequalisation tobe
independently setto compensate forthe appropriatelength of
cable.Internal pre-set controls allowadjustment ofthe
amplifierhighfrequency response, optimization ofthe
longitudinal hum rejection, and outputstageD.C.component.
The VA-100NC is operatedfromnegative 48V D.C.
Equipment provided:-
1 VA-100NCVideoDistributionAmplifier
1 SlideTray
1 RB-1NRearAssembly
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ACCESSORIES AVAILABLE
F-100D ModuleMountingFrame :-
Providesmounting forupto10
VA-100NCamplifiersside by side
in 134mm of standardRackspace.
(3 Rack Units)
TME-1AModuleExtender:Enables a module
to be operated in position and provide
access toall circuitboards,transistors
and internaladjustments.
RB-1NRearAssembly: An additionalrear
assembly maybe purchased to permit
benchtesting and servicing ofthe
amplifier withoutdisturbing the
rearassembliessuppliedwith the
amplifiers.
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SPECIFICATIONS
Inputpower
INPUTCHARACTERISTICS
Inputimpedance
Inputconnector
Longitudinal hum rejection
Maximum level
TRANSFER CHARACTERISTICS
Overallgain
High Frequency response
Differentialgain
Differentialphase
Noise
Operatingtemperaturerange
Cable equalisation
OUTPUT CHARACTERISTICS
Number
Impedance
Returnloss
Overload
DC on output
OutputConnector
FRONT PANELFACILITIES
47to53VDC (+veearthed) @
125mA in accordancewith
Telecom AustraliaSpec1002.
Bridging loopinputwith
returnloss>40dB to 6MHZ
1.6/5.6
>40dB
>2V p-p( OdB gain)
>+ 3dB
+ O.ldB to 10MHz
+ 0.2dB to 20MHz
bandwidthexceeds30MHz
<0.5% at 4.43MHz
o
<0.5 at 4.43MHz
>70dB 10kHz to 5MHzunified
weighted
oo
10 C - 55C
Frontpanelcontrolequalising
up to 300m of 75ohmcable
6, dc coupled
75ohms, sourceterminated
>40dB to6 MHz
3.0V p-pon 4.43MHz sinewave
2.5V p-pon pulse
adjustable to0V
1.6/5.6
* Gainadjustment
* Cableequaliseradjustment
* Clamp on/off indication
* Fuse
* Power onLED
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CIRCUITDESCRIPTIONRefer to Drawing no. 802995.
The blockdiagramshowsthat the VA-100NCcomprises :-
(a)An input stage:- which hasa highinputimpedance to
bridge the videosource, an equaliser for correction of input
coaxial cablelosses, anda 75ohm sourceterminatedoutput.
(b)A "plug-in1 area: - for accessories not
Link 2 bypassesthis feature.
yet defined.
(c)An output stage:- with 6 75ohm sourceterminated
outputs.Thisstage may have its blacklevelclamped to0Vby
placing LK1 inthe 'On' position.
(d) Clamp logic:- a syncseparator and backporchsample
pulse generator isfed from the output ofthe Inputstage.Video
from the output ofthe Outputstage is firstly low passfiltered
(to removechroma and noise) and thenapplied toa sampleswitch.
This switch, undercontrol ofthe samplepulse stores ina sample
and holdcapacitor the backporcherrorsignal. If LK1 isinthe
'On' positionthiserror is applied tothe invertinginput ofthe
Outputstage to correct the offset.
(e) Power Supply:- the -48V DC inputvoltage isfedviaan
on boardfuse toa DC-DCconverter. The output ofthe converter
is + and- 15V.Thesesupplies are furtherregulated to+ and-
12V by3 terminalregulators. TheLEDonthe frontpanel is wired
in series with a zener diodebetween +12and-12 Volts. The zener
is to ensurethat theLED extinguishes ifanyoneofthe
regulatorsfails.
Video Clamp
On
LK1
enablesback
porchclamp
Off
disables back
porch clamp
Accessories
Inserted
LK2
by-passes
accessories
Removed
accessories can
be inserted
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INSTALLATION
The VA-100NC is suppliedwith a slidetray,rearassembly and
associated hardware, for mounting inan F-100D frame.
SlideTray
The slidetray isa shallowtraywhichsupports the amplifier
in the frame. Itis mounted onthe front and rearcrossmembers
of the frame andis fixed in placewithsteelclips(speed nut
type)provided.
RearAssembly
The rearassembly is mounted onthe rear ofthe framewith
the screwsprovided.Careshould be taken notto overtighten
thesescrews, as excessiveforcewilldamage the thread inthe
mountingframe.
SignalConnections
Signalconnections are made via coaxialconnectorsmounted on
the rearassembly. The inputloop, ifnot usedshould be
terminated in75ohmas should any unusedoutputs ofthe
amplifier.
SETTING UP PROCEDURE
The amplifiershould besetupinthe position in which itis
intended tobe operated.Adjustments can then be madeusing the
intendedlengths of cable and with all outputsterminated as they
would bein service.
The cableequalizingshould besettoits minimum andthe
gain controladjusted to give the required low frequencygain.
Using a suitabletestsignal,such as pulse and bar,multiburst
or sweep, the cableequalization canbe advanced to compensate
for inputcablelosses.
It should be notedthat the equalizers are factory setto
match Beldentype8281 75ohm cable.
Whilst for short runs thisequalizerwill be satisfactory for
most 75ohm soliddielectriccables, for longerruns of some
cables the equalizer may have tobe reset (a factoryadjustment)
or replacedwith a speciallydesignedmodule.
If backporchclamping is required LK1 should beputinthe
'Clamp On1 position andthe Clamp OnLEDonthe frontpanel
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shouldilluminate. If clamping isnot required LK1 should bein
the 'Clamp Off position.
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MAINTENANCE
Oncehavingbeenadjusted the VideoDistributionAmplifier
will needlittleattention. Itis wisehowever to occasionally
check the adjustments as describedearlier.Thiswillalso be
necessaryafter a component has beenreplaced.
Mostfaults canbe readilytraced by checking the B.C.
voltages at variouspoints inthe circuit. The table of voltages
given in this book canbe used asa guide but deviations
sometimes inthe vicinity of +/-1volt canbe expected in some
units. The voltagesshould be checkedstartingfrom the input as
the B.C. conditions ofthe wholeamplifier aresetinthe first
stage, thus a faultearly inthe circuitwillcauseerrors atthe
output.
InternalAdjustments
The followingadjustableresistors and capacitors are
factory setand should notbe adjustedunless a component has
beenchanged.They arenot 'operational1 controls.Before
adjusting anyof thesecontrolsallowtime forthe VA-600 to
reach temperaturestability.
RV3 Hum:-
Adjusted to bestcancel humonthe inputcable. The clamp
must notbein operationduringthisadjustment.
RV1 BC Offset:-
With no inputsignalapplied RV1is used tosetthe junction
of R12R14to zerovolts.
C2 Freq Resp:-
Used tosetthe frequencyresponse ofthe inputstage to
maximal flatnesswhenobserved atthe junction ofR12 R14.
RV4 BC Offset:-
With no inputsignal and with LK1 installed and after
adjustment of RV1, RV4canbe adjusted so that the junction
of R29R30is zerovolts.
C5 FreqResp:-
Used tosetthe frequencyresponse ofthe outputstage.
Maladjustment of thiscapacitor can causeinstability inthe
amplifier underextremeconditions.
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TABLE OF VOLTAGES
Q Emitter Base Collector
1 -0.72 ~0 11.2
2 -0.66 ~012
3 12 11.30.82
4 0.240.82 12
5 -0.25-0.85 -12
6 -0.67 ~0 11.3
7 -0.66 ~012
812 11.31.65
9 0.3 0.98 12
10 -0.2-0.85 -12
11 1.0312.6 12
120 0.670.21
130 0.670.26
14 0.6 0.46-11.97
15 0.981.65 12
16 -0.68 ~012
U12345678
3 ~00 ~0-12 -11.9-0.5 12 -0.14
4 11.94 0 0 -12 -11.65 0 12 11.94
5 150 12
6 0 -15-12
All voltagesmeasuredwith a highinputimpedancemultimeter
under conditions of unitygain. All voltages are measuredwith
respect to earth.Supplyvoltage is -50.0V B.C. Testsignal is IV
P-P compositeStairStep andthe Clamp is off.
802995 10
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