SENDER A.M. Transmitters

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SENDER A.M. Transmitters
SENDER
SENDER S.A.
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SENDER S.A.
SENDER

• Company was created in 1997 by a group of
  engineers and
• technitians with long experience in Solid state
  A.M.
• Transmitters.
• Located in Santiago Chile, with 25 employes.
• 40 of them are shareholders.
• Main activity Design and manufacturing of A.M.
  transmitters,
• antenna tuning units, duplexers and triplexers.
• First transmitter in operation Nov 1997.
• Transmitters sold up to now127 from 1 KW to
  12.5 KW.

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Product Line
SENDER
AM 1500 SS 1.5 KW/1.1 KW, single phase / 2
power amplifiers AM 3000 SS 2.25 KW/3KW,
single phase or 3 phase / 4 power amplifiers.
AM 7500 SS 5.5 KW/ 7.5 KW, 3 phase or single
phase / 7 power amplifiers.

AM 15000 SS
11 KW/13 KW,3 phase / 14 power amplifiers AM
25000 SS 22 KW/26KW, 3 phase / 28 power
amplifiers A.T.Us for 1.5 KW, 3 KW,7.5 KW, 13 KW
and 26 KW
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Product highlights
SENDER

• Solid State. Modular / redundant
• architecture
• High efficiency. PWM class D R.F.
• amplifiers
• Hot plug in power amplifiers with Mosfets.
• Simple design with standard components.
• Totally rustproof cabinet made of iridated
• aluminum with stainless steel hardware.
• Excellent specs and audio quality.
• Outstanding factory support.
• Very competitive price.

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Basic specifications
SENDER
Frequency range .53 MHZ to 1.7 MHZ. Input
voltage 110V or 220 V single phase, 220V or 380V
3 ph or - 10. Line frequency 47HZ to 63
HZ. Efficiency 75 or better for single phase
transmitters, 80 or better for 3 phase
transmitters. Frequency response Better than
or- 1 dB 30 Hz to 10 KHZ. Distortion Less than
1 at nominal power and 90 modulation. Harmonics
and spurious- 73 dB or better for AM 1500
SS, - 80 dB or better for other
models.
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Frequency stability- 5 Hz. Output impedance
50 Ohm Dimentions and weigths AM 1500 SS
W44 cm,H62.5cm D60 cM , 100 Kg.
AM 3000 SS W44 cm,H65.5cm D60 cM , 160
Kg. AM 15000 SS W80 cm,H181cm
D81 cM , 500 Kg.
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Standard features 2 power level with
independient adjustment and modulation
autotracking. Start, stop,power level
selection and power level adjustment
remotely controled. Automatic alarm
reset. Positive and negative limiter.

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Basic block diagram
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Combiner
A1
Synth
Output
A2
Filter
Out
PWM
An
Control
PWR
Supply
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Relationship with RICHARDSON ELECTRONICS
SENDER

• Exclusive representation for Asia and other
  specific countries.
• Joint project to manufacture transmitters in
  U.S.A.
• Sender sells Omnicast F.M. Transmitters in Latin
  America.
• Excellent level of personal contacts .

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Near future projects
SENDER

• FCC type acceptance.
• Frequency agile 1.5 KW transmitter.
• IBOC compatibility.
• Inboard audio processor and modulation monitor.
• Higher power amplifiers

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Reliability in A.M. stations
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Introduction
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Station Concept

• Harmonic set of
• Transmitter
• Radiating system
• Energy System
• Auxiliary Equipment

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Experience with stations using Solid State A.M.
Transmitters
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• Very high reliability if precautions related with
  the following topics are considered
• Antenna discharges
• A.C. Source transients and discharges
• A.C. Source voltage limits
• Load stability
• Interference from nearby stations
• Reliability is reduced in unprotected stations

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Basic elements of a station
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ANTENNA
Audio Rem. Ctrl.
RF
H.V TRANSF.
DISTR. BOARD
T.P.
A.C.
GROUND PLANE
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TRANSMITTER BASIC BLOCKS
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• POWER SUPPLY
• PWM MODULATOR
• R.F. DRIVER
• CLASS D or E
• R.F. OUTPUT FILTER
• CONTROL,PROTECTIONS,SIGNALING
• EXTERNAL INTERFACE

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PWM MODULATOR
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• GENERATES D.C A.C. VOLTAGE FOR THE R.F. AMP.
• SWITCHING DEVICE, HIGH EFFICIENCY
• A FILTER IS NEEDED TO ELIMINATE SWITCHING
  FREQUENCIES
• CONMUTATION FREQUENCY IS 72 KHZ.

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PWM (PULSE WIDTH MODULATION)
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SIMPLIFIED DIAGRAM
R.F. AMPLIFIER
D.C. SUPPLY
Switch (Mosfet)
PWM FILTER
LOAD
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PWM BASIC OPERATION
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• Between 1) y 4) duty cycle is increased
• Mean voltage in the load increases
  proportionally
• A filter is required to remove high frequency
  components

F 72 kHz
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PWM Frequency spectrum
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Amplitude
D.C Component
PWM 0
Audio
Frecuency
72 kHz
144 kHz
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PWM Frequency spectrum
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Amplitude
D.C. component
PWM 180
Audio
72 KHZ components out of phase
Frecuency
144 kHz
72 kHz
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PWM filter diagram
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PWM filter frequency response
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PWM filter response sensibility to load changes
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Rload /- 15
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Load change consequences
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• With reduced load (Rloadlt Rnominal) transmitter
  will produce high frequency submodulation
• With increased load (RloadgtRnominal) transmitter
  will show high frequency overmodulation
• Distorsion will increase if filter is not
  propperly loaded.

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Modulated class D R.F. Amplifier.
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V
T1
T3
RL
T2
T4
PWM filter
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Class D r.f. Amplifier diagram
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Class D Bridge parasitic elements
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V
RL
Ciss Cgs Cgd
Crss Cgd
Coss Cds Cgd
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Mosfets drive
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Vgs
Dead time
V
T1
T3
Vgs(thr)
RL
time
T2
T4
Vgs peak 13V
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R.F. drive circuit
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• Ls and Cs series resonant
• Lp paralel resonant with mosfet input capacitance
  (Partially)

Ls
Cs
MOSFET drive
Drive signal
SCgs
Lp
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Class D bridge current paths
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V
T1
T3
RL
T2
T4
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Class D bridge undisered current paths.
V
V
T1
T3
T1
T3
RL
RL
T2
T4
T2
T4
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Class D Amplifier basics.
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• Low impedance driver required for
• Fast switching
• Low Vgs modulation by Crss
• Tuned load to produce sinusoidal current
• High efficiency (gt95 )
• Duty cycle should be lt 0.5
• Avoid transversal currents
• Coss charge and discharge through Rl

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Class D R.F. Amp typical waveforms.
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MOSFET characteristics
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• No secondary breakdown
• positive temperature coeff. Of Rdson (Simplify
  parallel operation)
• Voltage controled device (Vgs)
• Driver impedance dependent switching times.
• Intrinsic antiparallel diode

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IRFP350 MOSFET
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• Rdson 0.3 ohms
• Vdss 400 Vdc
• Vgs /- 20 Vmax Vth 3 V Vsat 9 V
• Id 16 A _at_ Tc25ºC 10 A _at_ Tc100ºC
• Idmax 64 A
• Capacitance _at_ f1MHz, Vds25V , Vgs0V
• Ciss 2600 pF (2400 pF for Vdsgt40V)
• Coss 660 pF (200 pF for Vdsgt40V)
• Crss 250 pF (50 pF for Vdsgt40V)

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Class D amplifier example
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Class D Simulation(1/2 bridge,Vmaxlt400x.75/2.5)
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• Operational data
• RL 15 ohms
• Po 132.36 W
• h 97.93
• Transistor stresses
• Vmax 110.81 V
• Imax 4.12 A
• Pdis 0.70 W x2 (1.4 Wtotal)

• Cicuit data
• Vdc 110 V
• F 1600 kHz
• d 0.43
• Transistor IRFP350
• Rdson 0.3 ohms
• Ton 16 ns
• Toff 40 ns
• Coss 200 pF
• L2 7.04 uH
• C2 1.55 nF

Simulated with HB plusfrom Design Automation
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Class E Amplifier diagram
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Class E amplifier example
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Class E amplifier basics.
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• R.F.Choke large enough to produce constant
  current
• High Q series resonant circuit to produce
  sinusoidal current
• Vds y dVds/dt 0 prior to starting conduction
• High efficiency (gt95)
• if special high voltage transistors with low
  Rdson are used

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Clase E Waveforms
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Clase E Simulation(Vmaxlt400x.75/2.5)
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• Circuit Data
• Vdc 33 V
• F 1600 kHz
• d 0.48
• Transistor IRFP350
• Rdson 0.3 ohms
• Ton 16 ns
• Toff 40 ns
• Coss 200 pF
• L112.3uH L23.7uH
• C1 4.1nF C24.9nF

• Operational Data
• RL 7.3 ohms
• Po 125.27 W
• h 90.53
• Transistor stresses
• Vmax 118.79 V
• Imax 9.84 A
• Pdis 6.55 W x2 (13.1 Wtotal)

Simulated with HEPA Plus from Design Automation
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Passband Output filter
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• Reduce R.F. Harmonics
• High third harmonic att gt 80 dB
• Medium second harmonic att. gt 40 dB
• Higher harmonics att gt 70 dB
• Permits impedance matching between amplifier and
  load.
• Atenuates low frequency components (Lightning
  protection)

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Output filter
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• Design oriented to protect R.F.amplifier
• Low frequency attenuation
• Inductor input
• Strategically located sensors
• Spark Gap Transient suppressor
• SWR Overpower
• Overcurrent Phase
• Input transient suppressor(Active or pasive)

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Output filter diagram
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Output filter frequency response
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Real and imaginary part of filter input impedance
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Protections integrated in the output filter
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Posible Transmitter Agresions
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• Antenna
• Impedance change and discharges
• A.C. Supply
• Voltage variation and transients
• Program signal
• Level variations and transients
• Ground
• Transfered potentials and high ground currents

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Antenna related problems
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• Impedance change
• Low heigth antennas are particularly unstable
• Restricted bandwidth
• Interference from other stations
• Discharges

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Short antenna example
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60 m tower operating at 700 kHz ZL 8 - j160 Q
20 Electrical length 50.4º
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Type T -90º Standard A.T.U.
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4.55uH j20
40.9uH j180
Zin 50j0
ZL 8-j160
11.37nF -j20
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A.T.U.Sensibility to antenna impedance changes
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Change in XL (/- 10 ohm6) if
ZL8-j150 Zin19.5-j24.4 SWR3.26 if
ZL8-j160 Zin50J0 SWR1 if Zl8-J170 Zin19.5
j24.4 SWR3.26 Change in RL ( /- 1 ohm
12.5) if ZL7-j160 Zin57.1j0 SWR1.14 if
ZL9-j160 Zin44.4j0 SWR1.14 RL and XL
simultaneous variation if ZL7-j150 Zin18.8-j26.
8 SWR3.52 if ZL7-j170 Zin18.8j26.8 SWR3.52 i
f ZL9-j150 Zin19.9-j22 SWR3.10 if
ZL9-j170 Zin19.9j22 SWR3.10
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Complex A.T.U. (dual T)
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j5
j145
j50.5
-j44.9
Zin 50j0
ZL 8-j160
20-J13
j37
-j92.5
-20
20
Variations in XL if ZL8-j150 Zin50j62.5 SWR3
.26 if ZL8-j160 Zin50j0 SWR1.00 if
ZL8-j170 Zin50-j62.5 SWR3.26
Note SWR of 8/-j10 refered to a 8j0 is 3.26
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Load ladder
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RF amplifiers
50 Ohm
Antenna
Z1
1
combiner
A.T.U.
filter
Zn
n
15 Ohm
Extreme values for SWR 11.5, refered to 50 Ohm,
are 33.3j0 75.0j0 50-j20.4 50j20.4
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Load variation effects
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Class D amplifier
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A.T.U. And amplifier stresses
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A)ZL50-J62.5 Eff93.5 Po4.5W
Ip15.5A B) ZL50J62.5 Eff90.9 Po2.02W
Ip1A C) ZL19.5J24.4 Eff84
Po44W Ip105A D)ZL19.5J24.4 Eff93.8
Po395W Ip73.7A
2020
90
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Class D waveforms
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Ro15 VSWR11
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Class D waveforms
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Ro15-j6.1 VSWR11.5
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Class D waveforms
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Ro15j6.1 VSWR11.5
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Class D waveforms
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Ro22.5 VSWR11.5
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Class D waveforms
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Ro10.0 VSWR11.5
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Atmospheric discharges
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• At the antenna
• In A.C.lines
• In telephone lines

Characteristics
Imax 200 kA Itypical 10 a 20 kA
dI/dT typical 10 kA/useg
Risetime 2 useg Decay time40 useg to 50
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Criteria to minimize damages
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• Disipators
• Avoid charge acumulation using sharp points
• or active systems
• Well designed grounding system
• Low impedance direct paths
• High impedance undesired paths
• Radial equipotential conections
• Antenna and ground conection closely located at TX

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Discharge probability function
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N 15 L (CHh)2 10-6
N Discharges per year L Ceraunic level (Nº of
days per year when thunderstorms are heared) C
Site topographic index (0 to 0,3) H Site mean
heigth above surroundings (1 to2 km) h Antenna
heigth
Example C0.1 L50 H100m h120m N
12.7 discharges per year.
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Discharge current circulation
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1
3
2
1. Strike 2. Antenna 3. Discharge through
the antenna 4. Guy 5. Isolator 6. Spark
gap 7. Ground rod 8. Base insulator 9.
Cnecting Loop 11. A.T.U. isolator 12. A.T.U. 13.
Ferrite core 14. Coaxial cable 15. Discharge
current in caxial cable 16. A.T.U. Spark gap 17.
Disipator
4
9
13
15
14
11
12
5
6
8
16
7
10
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Equipment Instalation
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Reference ground
Coaxial cable
A.C. Line transient protector
A.C. mains
Panelboard
Ferrite toroids
Ground to auxiliary equipment
Transmitter A.C. line
Building ground
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Ground system equivalent circuit
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Discharge voltages and currents
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Interference
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1.- Intermodulation products are generated 2.-
SWR protection is desensitized 3.- Dangerous
voltages at the R.F. Amplifier and output
filter maybe generated.
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Transmitter Protections
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• A.C.input
• Overload
• Short cicuit
• Transients
• Overvoltage
• Undervoltage
• Assimetry
• D.C.supply
• Overload
• Transients
• Failure

• R.F.
• Overcurrent
• SWR
• Phase
• overpower
• Transients
• Internal
• R.F. Drive Temperature
• PLL

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Factory tests to ensure transmitter reliability
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• Power amplifiers
• Long time operation at 150 modulation
• Output
• Open cicuit
• Short circuit
• Simulated lightning strike
• SWR
• A.C. input
• Phase failure
• Simulated transient
• Voltage variationSENDER

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Conclusions
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Reliability in a transmitting sytem is a function
of

• Transmitter intrinsic reliability
• Power stages regimes much lower than devices
  limits
• Simple low power stages with low number of
  components
• Rational protections adjustment

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Conclusions
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• High quality station engineering
• A.C. Transient protection
• Antenna discharges protection
• Well dimentioned and coordinated grounds.
• Stable radiating sysytem.
• Interference filtering
• Coordination with the manufacturer

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Recomended instrumentation for test and adjustment
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1.- To measure resonance 1.1 R.F.Generator
1.2 Oscilloscope or spectrum analyzer 2.-
To measure R.F.impedance 2.1 R.F. bridge
(General Radio 1609 or Delta OIB-3) 2.2
R.F. generator (Delta RG3-A or similar) 2.2 Spe
ctrum analyzer (HP 8553B or similar) or
detector included in RG3-A
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2.3 An H.P. vector impedance meter may be used
instead of 2.1,2.2 and 2.3
3.- To measure power 3.1 R.F. Dummy load,non
inductive or with a tuning network to
adjust it to 50J0 Ohm. 3.2 R.F. Ammeter (Delta
TC-1 or similar) or R.F. Wattmeter 4.- To
measure frequency response and distortion 4.1 Ge
neral purpose oscilloscope, 2 channel 4.2 Audio
analyzer (Audio precision Portable One or
similar) 4.3 Modulation monitor (H.P. 8901 A or
B , Belar AMM3, TFT 923 A.M. or similar.)
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5.- To measure spectrum.- 5.1 Spectrum analyzer
100KHZ.to 50 MHZ or more TEK 2711, H.P. 8553B
plus display unit or similar). 5.2 R.F.
atenuator. 5.3 OPTIONAL. Notch filter to remove
the carrier frequency and avoid
intermodulation 6.- To check efficiency. 6.1
A.C. Analyzer.(To measure A.C. voltage, current,
power and power factor
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7.- To measure transmitter carrier frequency.
7.1 Digital frequency meter up to 10 MHZ. Or
higher frequency, time base 1 P.P.M. or
less. 8.- To measure temperature. 8.1 Infrared
temperature measuring unit with suitable
digital multitester. (Fluke). 9.- For
general voltage and current measurements 9.1 Tru
e RMS digital multimeter, suitable to operate in
high R.F. fields. (Our best experience is with
Fuke Digital multimeters.)
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10.- For long run test. 10.1 USASI Noise
generator. (Delta SNG-1).
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SENDER
Pablo Phillips D.
Agosto 1999