TFT 923 User manual

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EFFEC :
OPERATIO; MAINfE ANC
MOD L923
AM MODULA: -- ON ONITO
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,ca..,..., .. ....., c,i ..... VIl,LAGE D
I , A CLARA, C 950
: (408) 7 7-7272
~ ( 08 727-.59

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CONTENTS
Section I - General Inf onnation
Paragraph Title Page
1.1 Equipment Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
1.2 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
1.3 Warranty Information .. ........ .. .......................... 14
1.4 Claims for Damage in Shipment . . .. ..... . .. ......... .. . ........ 1 -5
Section II -Imtallation
2.1 Unpacking and Inspection .............. ... . . ............. ... . 2-1
2.2 Power Requirements ... . .............. ........ . . . . . . ....... 2-1
2.3 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Section m-Operation
3.1 General Information . .... ..... . . . .. . ........ . .. . ........... 3-1
3.2 Tum - on and Warm-up ............... . ......... . . . .......... 3-1
3.3 Controls, Indicators and Connectors . ..... ........... ...... ...... 3-1
3.4 Modulation Measurement Using MODULATION Meter .......... .. ..... 3-5
3.5 Modulation Measurement Using Peak Indicators . . ............ . . . . . ... 3-5
3 .6 Residual Noise Measurement .... . . ...... ........ . ...... ....... 3-5
3.7 Distortion Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3-8 Carrier Power Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3-9 Modulation Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Section IV -Theory or Operation
4.1 Block Diagram Description . . . . . .
... . . .... . ...... ... .......... 4-1
4.2 AM Detector, Lowpass Filter, and Summing Amplifier .... ...... . ....... 4-2
4.3 Audio Attenuator .. . . . . ............ . ..... .. ...... . ........ 4- 3
4.4 Carrier Level LED Drivers ............ . ......... . . . . ....... . . 4- 3
4.5 Audio Amplifiers ....................... .... ............. . 4-3
4.6 Modulation Meter Amplifiers ....... .. ....... ..... .. ...... ..... 4-3
4.7 Peak Flashers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.8 Calibration Signal Generator ....... . . . . .. ............ . ....... . 4-5
4.9 Pow er Supplies .......... . ...... .. .................. . . . .. 4-5
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CONTENTS (Continued)
Section V -Maintenance
Paragraph Title Page
5.1 General Information .............. .... ..... .... ....... . . . . . 5-1
5.2 Periodic Maintenance ........ . . . .... . . ... .. . .......... ..... 5- 1
5.3 Meter Lamp Replacement
.... . ... . . . ..... ..... ... . ..... ... . . . 5-1
5.4 Calibration Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5.4.1 Audio Attenuator Circuit .. .. ...... ..... .. . ...... . . . . . ... 5-1
5.4.2 Carrier Level Indicators ... ....... . ... ....... . . ......... 5-2
5.4.3 Peak Flashers ........... ..... ................. . . . . • . 5- 2
5.4.4 Modulation Meter ......................... ... ... . .... 5-2
5.4.5 Carrier Power Alarm . . ........... • . ..... . ............. 5-2
5.4.6 Modulation Alarm ................. ... . . ..... • . . ...... 5-2
Appendix A - RF PreseJector Option
(See separate table of contents provided with Appendix A)
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Illustrations
Paragraph Title Page
1.1-1
TFf Model 923 AM Modulation Monitor - Basic Block Diagram . . . . . . . . . . . 1-1
3.3-1 Front Panel Controls and Indicators ..... ... . ........ .... ....... 3-1
3.3-2 Rear Panel Controls, Indicators and Connectors . .. ................ .. 3-3
Tables
Paragraph Title
3.3-1 FrontPanel Controls and Indicators Page
3-2
3.3-2 Rear Panel Controls, Indicators and Connectors . . . . . . . . . . . . . . . . . . . . 3-4
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6-2
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6-5
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CONTENTS (Continued)
Section
VI -Engineering Drawings
Title Dwg No . Rev.
AM Monitor Model Assy .................. 5102-3879 . . . . . . . . . . B
AM Monitor Front Panel Assy . . . . . . . . . . . . . . .
AM Monitor Chassis Assy . . . . . . . . . . . . . . . . . .
AM Monitor System Block Diagram . . . . . . . . . . . .
AM Monitor Main Board Schematic Diagram . . . . . .
AM Monitor Main Board PCB Assy . . . . . . . . . . . .
5102-3880
5102-3881
6600-2764
6601-3946
6608-3946
. . . . . . . . . . A
. . . . .. . . . . B
....... ... A
. . . .. . . ... A
..... . . ... A
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CONTENTS (Continued)
Section
VII - Parts List
Section Title Dwg No. Rev .
7-1 Main BD PCB Assy .... ... ... ... ..... . . . . 6608-3946 .......... A
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Secti on I
GENERAL INFORMATION
1.1 EQUIPMENT DESCRIYI'ION
The TFT Model 923 AM Modulation Monitor is intended for continuous modulation
monitoring
of an AM transmitter operating in the 500kHz to 40 MHz frequency range to enable
the station tocomply with therequirements
of Section 73. 56 of FCC Rulesand Regulations. The
Monitor requires a minimum I-volt nns RF input from the monitored transmitter. No tuning is
required
at the Monitor.
Features include:
• Flasher to indicate 125
% positive modulation peaks.
• Adjustable flashers to indicate positive modulation peaks from 50% to 150% .
• Adjustable attenuator for reading residual noise and low modulation percentages on
modulation meters.
•
Linear phase filter design, eliminating overshoot on complex audio waveforms.
• Wide audio bandwidth, allowing distortion measurements on high frequency
modulation.
• Internal calibration circuit which digitally synthesizes a modulated carrier for both
+125% and -100% modulation to check the modulation meter and peak_flashers.
An optional, tunable
RF Preselector can be installed in the Monitor for off-the-air
monitoring
of signals in the 500 to 1990kHz range. Figure 1.1-1 is a basic block diagram of
the equipment.
"'
[7
ANTENNA INPUT
500 kHz to 1990kHz -
HIGH LEVEL
RF INPUT
500 kH zto 40 MH z -
-
110/220V
AC INPUT -
-
PRES EL EC T OR BOARD
(OPTIONAL)
j
DC POWER
MAIN BOARD
POWER
SUPPLY -
-
455 kHz
I F
Figure 1.1-1. TFT Model 923 AM Modulation Monitor -Basic Block Diagram
1-1

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1.2 SPECIFICATIONS
RF INPUT, WIDE BAND DEMODULATOR
Frequency Range . . . . . . . . . . . . . . . . . . . . .
High-Level RF Input
...... . . . . . . . . . ... .
Impedance ........ . ....... . ....... .
MODULATION METER/TEST/RIGHT
Meter Range . . . . . . . . . . . . . . . . . . . . . . . .
Attenuator
Range . . . . . . . . . . . . • . . . . . . . .
Accuracy .............. . ... . . .. ... .
Frequency Response . . . . . . . . . . . . . . . . . . .
MODULATION METER/LEFf
Meter Range . . . . . . . . . . . . . . . . . . . . . . . .
PEAK MODULATION INDICATORS
1 25 % Peak Indicator . . . . . . . . . . . . . . . . . . .
Variable Peak Indicator ........... .. . . . .
Accuracy (400 Hz Tone) .. .............. .
Frequency Response (high le ve l RF i nput)
Response Time Accuracy
500
kHz to 40 MHz
1 V to 5 Vrms
50 ohms
0 to 133% with "dB" scale for
measurement of positivemodulation
or the right channel.
0 to- 50
dB in 10 dB steps
+2.0% at
100% modulation,
sinusoidal test tone 400
Hz
50 Hz to 15 Hz ±2 .0%, 30 Hz to
25 kHz, ±5.0%
0 to 133% and "dB" scale for
monitoring negative modulation or
the left channel
Internally set to
flash when
modulation exceeds + 125 %
Set
by the front panel 3-digit switch
in 1% steps from 50% to 150% on
both positive and negative peaks
2% at 98 % modulation
±3%,
50 Hz to 15 kHz at 98%
modulation
Approximately
10 cycles of 10 kHz
1 -2

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MODULATION CALIBRATOR
Type: . . . . . . . . . . . . . . . . . . . . . . . . . . . . Built-in modulation calibrator
generates a "-" 100
%, "+ " 125 %
AM modulated carrier which is
switched into the detector input by
the front panel "CAL" button
Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . ±1.0%
Audio Outputs, Rear Panel
Impedance . . . . . . . . . . . . . . . . . . . . . . . . . 600 ohms. balanced, 5k ohms
unbalanced
Balanced Output Level . . . . . . . . . . . . . . . . . . 0 dBm (.775 Vrms)
Unbalanced Output Level . . . . . . . . . . . . . . . . 5 Vrms
THD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.15% typical, 0.25~ max at 99%
modulation, 400 Hz tone
Signal-to-noise Ratio . . . . . . . . . . . . . . . . . . . > 75 dB Below 100%
(high level RF input)
Transient Response . . . . . . . . . . . . . . . . . . . . <
1. 0%overshoot
(high level RF input)
Baseband Frequency Response . . . . . . . . . . . . . ±0 .5 dB , 20 Hz to 25 Hz
ALARM OUTPUT
Relay contactclosures for activation of an external alarm upon loss of modulation or carrier.
PHYSICAL AND ENVIRONMENTAL
Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19" W x 5 1/4" H x 14" D
Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 lbs. shipping weight
Power : . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115/230 VAC, 50 /60 Hz , 30 watts
maximum
Operating Temperature . . . . . . . . . . . . . . . . . . 0° to
50 °C
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1.3 WARRANTY
TFf inc.warrants each of the instruments of its manufacture to be produced to meet the
specificationsdelivered to
the BUYER; and to be free from defectsin material and workmanship
and will repair
or replace, at its expense, for a period of one year from the date of delivery of
equipment, any parts which are defective from faulty material or poor workmanship.
Instruments found
to be defective during the warranty period shall be returned to the factory
with transportation charges prepaid
by BUYER. It is expressly agreed that replacement and
repair shall be the sole remedy of BUYER with respect to any non-conforming equipment and
parts thereof and shall be in lieu of any other remedy available by applicable law. All returns
to the factory mu st be authorized by the SELLER, prior to such returns. Upon examination by
the factory, if the instrument is found to be defective, the unit will be repaired and returned to
the BUYER, with transportation charges prepaid by SELLER.
Transportation charges
for instruments found to be defective within the first (30) days of the
warranty period will
be paid both ways by the SELLER.
Transportation charges
for warranty return s, wherein failure is found not to be the fault of
the SELLER , shall be paid both ways by the BUYER.
This warranty does not apply to instruments which, in theopinion of theSELLER, ha ve been
altered
or misused.
NO OTHER WARRANTY IS EXPRESSED OR IMPLIED. TFf IS NOT LIABLE FOR
CONSEQUENTIAL DAMAGES.
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