Larcan DTT250M General Description Manual Download | Manualshive

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•

J6

interconnects

with

J5

of

the

Metering

board

for

the

AGC,

VSWR

cutback,

and

VSWR

shutdown

signals.

•

J7

is

the

connection

to

the

AGC

feedback

input

of

the

exciter.

The

transmitter

interlock

chain

begins

with

the

+12V

at

K1

‐

7.

When

K1

is

set

ON

by

energizing

its

coil

K1

‐

1,

contacts

7

and

12

close

and

contacts

7

and

10

open,

turning

off

the

LED

inside

the

OFF

button

S4.

The

+12V

from

closed

contact

7

‐

12

lights

the

LED

inside

the

ON

button

S3

and

lights

the

opto

‐

diode

in

U3D,

which

provides

a

logical

active

low

out

of

its

pin

10

for

a

remote

control

status

interface.

This

status

signal

simply

tells

the

remote

control

through

J5

‐

6

that

the

transmitter

was

instructed

to

be

ON,

nothing

more.

The

+12V

from

contact

7

‐

12

also

comes

out

of

the

board

on

J3

‐

5,

which

is

one

side

of

the

EXT

1

interlock.

EXT

1

in

larger

transmitters

is

often

used

with

a

fire

alarm

system

to

stop

all

blowers,

and

in

lower

power

transmitters

it

is

still

worthwhile

that

a

normally

closed

fire

alarm

contact

be

connected

to

EXT

1

because

the

fan(s)

in

the

transmitter

could

cause

enough

air

currents

in

the

transmitter

room

to

fan

the

flames.

When

the

EXT

1

interlock

is

closed

and

the

+12V

appears

on

J3

‐

4,

the

+12V

is

now

at

DS5

(marked

EXT

1)

and

the

opto

‐

diode

of

U3C

which

both

light

up

to

say

EXT

1

is

closed.

The

active

low

from

U3C

pin

11

informs

the

remote

control

via

J5

‐

14

that

EXT

1

interlock

is

closed.

The

+12V

now

is

applied

to

J2

‐

8

which

connects

to

a

normally

closed

contact

in

a

thermostat

that

responds

to

the

temperature

of

the

RF

power

amplifier.

If

a

cooling

fan

should

stop

and

the

amplifier

should

overheat,

this

contact

will

open

and

prevent

the

+12V

from

appearing

at

J2

‐

3.

This

of

course

breaks

the

chain

and

removes

the

12V

from

the

solenoid

of

the

power

supply

contactor.

Assuming

the

thermostat

is

cool,

DS4

and

the

opto

‐

diode

in

U3B

are

lighted,

confirming

TEMP

is

okay.

The

logical

active

low

out

of

U3B

pin

14

informs

the

remote

control

of

this

fact

through

J5

‐

7.

Next

stop

for

the

+12V

is

a

normally

closed

VSWR

lockout

relay

contact

connected

via

J1

‐

5

and

J1

‐

9

from

the

Metering

Board

(Prefix

5A,

K2).

This

relay

operates

and

the

interlock

chain

is

opened,

if

for

some

reason

the

transmitter

has

seen

a

large

amount

of

reflected

power

and

the

Metering

Board

VSWR

supervisory

circuit

has

repeatedly

tried

and

retried

to

keep

the

transmitter

on

and

finally

decided

"Enough!"

The

VSWR

lockout

relay

can

be

reset

from

RESET

button

S6,

or

by

the

VOR

Enable

and/or

Remote

ON

via

jumpers

E1,

E3.

Assuming

the

VSWR

is

low

and

5A

‐

K2

contacts

are

closed,

the

+12V

next

appears

at

J3

‐

3,

which

is

EXT

2

interlock.

This

is

the

place

where

RF

patch

panel

link

contacts

or

coaxial

switch

auxiliary

contacts,

and/or

dummy

load

thermostat

contacts

would

be

connected

so

that

the

transmitter

can

only

be

ON

when

valid

RF

paths

are

present,

consequently

the

EXT

2

path

from

J3

‐

3

to

J3

‐

7

will

be

intact.

Finally,

when

the

interlock

chain

is

complete,

the

+12V

is

applied

to

the

solenoid

of

the

power

supply

primary

contactor

through

J2

‐

10,

and

the

cooling

fans

and

power

supply

are

all

turned

on.

The

DS3

LED

marked

EXT

2

is

lighted,

as

is

the

opto

‐

diode

in

U3A.

The

output

active

low

from

U3A

at

pin

15

informs

the

remote

control

via

J5

‐

15

that

the

EXT

2

interlock

is

intact.

The

interlocked

+12V

is

also

available

at

J3

‐

6

so

it

can

be

used

for

special

on

‐

site

control

functions.

The

transmitter

control

circuit

permits

the

transmitter

always

to

be

turned

OFF.

Any

+12V

applied

to

the

K1

Reset

coil

at

pin

6

will

cause

the

+12V

to

be

removed

from

the

interlock

chain

discussed

above,

and

diverted

instead

to

the

LED

inside

the

OFF

button

S4.

The

fact

that

turn

off

is

possible

regardless

of

the

position

of

the

REMOTE/LOCAL

switch,

is

a

valuable

safety

feature

provided

in

all

LARCAN

transmitters.

The

transmitter

AGC

system

is

based

on

an

RF

attenuator

located

near

the

output

stage

of

the

exciter,

and

this

is

controlled

by

DC

voltage

supplied

from

RF

detectors

which

sample

the

RF

output

from

the

transmitter.

If

the

PUB96-32 Rev 2 August 29, 2005

32-2

TX Control Panel 40D1985G1

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Summary of Contents for DTT250M

Page 1: ...lid state amplifier This amplifier requires no tuning or adjustment within its band of operation Simplicity of operation reduced maintenance costs and increased reliability are a few of the major benefits derived from this modular amplifier This module is operated well below its maximum ratings The amplifier chain consists of three stages of amplification The preamplifier stage is a high gain broa...

Page 2: ... on 15 contact D shell connector J5 For local operation simply place the LOC REM switch in the LOC position For remote control operation the LOC REM switch must be in the REM position This places 12V on Remote E The Remote Enable 12V appears as an arming signal at J5 5 and the momentary connection of this 12V to J5 13 turns the transmitter ON and momentary connection of the 12V to J5 8 turns the t...

Page 3: ...CONTENTS 1 BANDPASS FILTER 2 2 RF DIRECTIONAL COUPLER 4 PUB96 26 Rev 1 September 13 2005 26 1 RF Output BP Filter Directional Coupler ...

Page 4: ...the trimmer produces a change of capacitance and the trimmer s moveable slug is shaped to appear as a shorted turn which alters the inductance of the helix Matching from and to 50 ohm transmission lines is accomplished with taps on the input and output helixes Coupling between sections is electrically a bridged T network of capacitors and is made up of the small capacitance between the free ends o...

Page 5: ...Figure 1 5 Pole Bandpass Filter Curves Figure 2 5 Pole Bandpass Filter Used in the TTS1000B PUB96 26 Rev 1 September 13 2005 26 3 RF Output BP Filter Directional Coupler ...

Page 6: ...ignated L1 through L4 They are in reality short pieces of Teflon sleeved magnet wire which although they may possess a fraction of a nanohenry of inductance are mainly small capacitors which are factory adjusted by bending the wire to control the amount of coupling capacitance between the transmission line and the sampling loop concerned The position of the capacitor along the loop does not seem t...

Page 7: ...Figure 3 Quad Directional Coupler Equivalent Schematic PUB96 26 Rev 1 September 13 2005 26 5 RF Output BP Filter Directional Coupler ...

Page 8: ...ER LOW BAND PUB96 28 Rev 2 Aug 2007 PA Module CONTENTS FUNCTIONAL DESCRIPTION 1 6 WAY SPLITTER INPUT BOARD 1 FET RF AMPLIFIERS 1 6 WAY COMBINER OUTPUT BOARD 2 VSWR CONTROL BOARD 2 GREEN LED SENSITIVITY ADJUSTMENT 5 ...

Page 9: ... provides input matching for the transition from the input connector to the input transmission line A built in detector CR102 and C147 is fed from a directional coupler on the input transmission line to provide a sample of the input signal for module gain monitoring R117 and R118 terminate the directional coupler FET RF Amplifiers References Figure 3 Figure 4 Figure 5 Figure 6 Each of the six ampl...

Page 10: ...se will blow in this case isolating the defective device from the rest of the module and transmitter power supply allowing the remaining devices to keep operating normally A blown fuse can serve as a valuable troubleshooting aid when trying to identify failed devices 6 Way Combiner Output Board Part number 40D1472G1 40D1472G2 References Figure 6 and Figure 3 The six amplifier outputs are applied t...

Page 11: ...s the control voltage set on pin 6 the output on pin 7 will go high R22 C10 and CR1 provide a fast attack slow release control voltage to Q2 when a high VSWR condition suddenly occurs This will turn on Q2 which turns on Q4 which quickly reduces the bias applied to the power amplifier FETs this reduced bias also reduces their gain and therefore their RF output and keeps the amplifier at safe levels...

Page 12: ...each companion bias potentiometer in the same manner for the proper bias current Install remaining fuses and remove the bias short after all bias adjustments have been made Low power sweep of amplifiers Note Low power sweep of PA modules should not be required under normal circumstances even when replacing FET devices There are no tuning adjustments on these modules Ensure that terminations are in...

Page 13: ...sition and adjust the exciter output power until the transmitter output power reads 110 Remove the module to be set up and remove the two front fuses from it in order to simulate a single FET package failure Replace this crippled module in the transmitter and apply a nominal 50 APL staircase video signal to the transmitter analog transmitters The green LED should now be extinguished if it is not r...

Page 14: ...f turn at a time to establish a known reference point Place the AGC MANUAL switch in the AGC position and with the RAISE LOWER switch readjust the transmitter output power to 100 Similarly the aural amplifier may be adjusted in the same manner but being an FM signal the modulation of the carrier is not critical ...

Page 15: ...W HIGH BAND 40D1493G3 PUB96 29 Rev 2 i 24 Oct 2008 CONTENTS FUNCTIONAL DESCRIPTION 1 6 WAY SPLITTER INPUT BOARD 1 FET RF AMPLIFIERS 1 6 WAY COMBINER OUTPUT BOARD 2 VSWR CONTROL BOARD G1 2 GREEN LED SENSITIVITY ADJUSTMENT 5 ...

Page 16: ...mission line A built in detector CR102 and C147 is fed from a directional coupler on the input transmission line to provide a sample of the input signal for module gain monitoring R113 and R117 terminate the directional coupler FET RF Amplifiers Drawing References Figure 3 through Figure 6 Each of the six amplifiers in the module consists of two source grounded N channel insulated gate Field Effec...

Page 17: ...of active devices such as these is short circuit and the fuse will blow in this case isolating the defective device from the rest of the module and transmitter power supply allowing the remaining devices to keep operating normally A blown fuse can serve as a valuable troubleshooting aid when trying to identify failed devices 6 Way Combiner Output Board Part number 40D1468G1 Drawing References Figu...

Page 18: ...ected and sensed at pin 11 of J1 to comparator circuit U2B R21 sets the level at which VSWR protection begins If the level of detected reflected power on pin 5 of U2B exceeds the control voltage set on pin 6 the output on pin 7 will go high R22 C10 and CR1 provide a fast attack slow release control voltage to Q2 when a high VSWR condition suddenly occurs This will turn on Q2 which turns on Q4 whic...

Page 19: ...mA for digital operation Remove the fuse Remove the side B bias short and place it on side A at the junction of C6 R2 R3 and R9 Place the fuse in side B Adjust the side B bias pot for the proper current Move the fuse to the remaining fuse holders one at a time and adjust each companion bias potentiometer in the same manner for the proper bias current Install remaining fuses and remove the bias sho...

Page 20: ...er output power until the transmitter output power reads 110 Remove the module to be set up and remove the two front fuses from it in order to simulate a single FET package failure Replace this crippled module in the transmitter and apply a nominal 50 APL staircase video signal to the transmitter analog transmitters The green LED should now be extinguished if it is not remove the module and adjust...

Page 21: ...ed one half turn at a time to establish a known reference point Place the AGC MANUAL switch in the AGC position and with the RAISE LOWER switch readjust the transmitter output power to 100 Similarly the aural amplifier may be adjusted in the same manner but being an FM signal the modulation of the carrier is not critical ...

Page 22: ... gain control of the input to each chain It therefore has components in place for adjustment of RF gain and phase to enable setting up these paralleled transmitters In a single chain transmitter such as the TTS1000B no requirement exists for control of RF phase nor consequently its components but our design standardization results in lower overall expense being incurred by simply leaving the compo...

Page 23: ...e overall system gain is sufficient to result in overdrive of later stages of the transmitter The transmitter or translator lineup may therefore include an in line attenuator in the RF chain ahead of the IPA module in order to prevent overdrive from certain models of exciter modulator U3 is a voltage regulator providing B to the amplifier and biasing for the varactor diodes RF isolation is provide...

Page 24: ... the values of R3 and R6 which have little or no effect at RF R3 and R6 provide a DC path for bias and provide loading at lower frequencies where gate impedance is high in order to assist in maintaining amplifier stability The choice of C6 C7 C20 and C21 values their series inductances and that of board traces also ensures effective bypassing at critical frequencies The output matching π network c...

Page 25: ...readjusted during system test for minimum intermods and FM noise 4 Connect a 30 dB 20 W attenuator to the output of the amplifier This will absorb amplifier output and protect the sweep detector Use it instead of the 20 dB pad shown in the diagram below 5 Reinstall fuses and apply B to both supply connections of the amplifier module 6 Apply a low level sweep to the amplifier and measure the DC inp...

Page 26: ...PUB96 30 rev 1 Jul 1 2010 30 5 1 kW IPA Assembly VHF 1 kW TTS1000B TRANSMITTER IPA ASSEMBLY 1 Sweep setup and response for IPA alone without preamp ...

Page 27: ...n applied to the gates The gate impedance at the operating frequency is much lower than R3 and R5 so these resistors have little or no effect at RF R3 and R5 provide a DC path for bias and provide loading at lower frequencies in order to assist in maintaining amplifier stability The choice of C2 and C6 values and their internal equivalent series inductances also ensures effective bypassing at crit...

Page 28: ... These will be the starting points the bias current settings and L9 will be readjusted during system test for minimum intermods and FM noise Disconnect the clip lead after adjusting bias currents 4 Connect a 30 dB 20 W attenuator to the output of the amplifier 5 Apply B to both supply connections of the amplifier 6 Apply a low level sweep to the module and measure the DC input current about 1 2 am...

Page 29: ...ent to cause the transmitter power output to decrease or even to momentarily turn off the transmitter The transmitter is provided with a VSWR cutback function that either reduces its power output to save it from harm in the event of gradual occurrences such as antenna ice build up or momentarily takes it off the air from random events Three VSWR events occurring rapidly in a short time will cause ...

Page 30: ...emote control of this fact through J5 7 Next stop for the 12V is a normally closed VSWR lockout relay contact connected via J1 5 and J1 9 from the Metering Board Prefix 5A K2 This relay operates and the interlock chain is opened if for some reason the transmitter has seen a large amount of reflected power and the Metering Board VSWR supervisory circuit has repeatedly tried and retried to keep the ...

Page 31: ...f a VSWR that exceeds a preset amount the AGC voltage becomes modified a little to reduce the transmitter output by an amount proportional to the reflected signal This VSWR Cutback permits the transmitter to remain on the air at reduced power if the antenna should gradually accumulate a layer of ice If the reflected power should exceed a much larger amount causing repeated momentary tripping off a...

Page 32: ...nificantly attenuates 3 58 MHz NTSC color subcarrier as well as any 4 5 MHz intercarrier that may be generated in CR1 or CR2 due to the presence of visual and aural RF signals together in the system Removal of these subcarrier components before the signal is peak detected enables the circuit to be responsive to sync peak pow only for visual or just CW aural power and relatively immune to undesired...

Page 33: ...tback mode which is what will need to be set up because it affects the exciter AGC and VSWR supervision The output from U1 U2 pin 7 is also applied to a second op amp U1 U2 pin 3 If the detected level at U1 pin 3 rises above the level set by the AGC pot on the Control board at U1 pin 2 the output on pin 1 will rise This AGC output is applied via J5 1 to a final buffer amplifier U2A on the Control ...

Page 34: ... TP1 drops to a minimum approximately 10 to 20 mVDC A DC coupled scope will make the adjustment easier to see the objective is to place the U1 output as near the op amp ground rail as possible without the op amp going into saturation Turning the pot farther will decrease the sensitivity of the system for small signals Once this minimum voltage has been reached do not re Reflect Power Meter Calibra...

Page 35: ...nergizes and the VSWR C B indicator LED on ulse After three pulses visible on the meter lock out and a red VSWR L O indication on the ontrol Panel should occur Check that RESET is possible using the RESET button S6 on the Control Panel A reads 20 2 0 This is about 17 to 18 dB below the full forward power output of the transmitter W the Control Panel lights up Replace the 16 dB pad with a 10 dB pad...

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