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

2. SENDER S.A. 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 now:127 from 1 KW to 12.5 KW.

3. Product Line AM 1500 SS 1.5 KW/1.1 KW, single phase / 2 power
SENDER
Product Line
AM 1500 SS 1.5 KW/1.1 KW, single phase / 2 power
amplifiers
AM 3000 SS 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 SS 11 KW/13 KW,3 phase / 14 power amplifiers
AM 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

4. Product highlights Solid State. Modular / redundant architecture
SENDER
Product highlights
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.

5. Basic specifications Frequency range: .53 MHZ to 1.7 MHZ.
SENDER
Basic specifications
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.

6. Frequency stability:+- 5 Hz. Output impedance: 50 Ohm
SENDER
Frequency stability:+- 5 Hz.
Output impedance: 50 Ohm
Dimentions and weigths:
AM 1500 SS W=44 cm,H=62.5cm
D=60 cM , 100 Kg.
AM 3000 SS W=44 cm,H=65.5cm
D=60 cM , 160 Kg.
AM SS W=80 cm,H=181cm
D=81 cM , 500 Kg.

7. 2 power level with independient adjustment
SENDER
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.

8. Basic block diagram A1 Combiner Synth A2 Output Filter Out PWM An PWR
SENDER
Basic block diagram
Combiner A1
Synth
Output A2
Filter
PWM
Out An
PWR
Control
Supply

9. Relationship with RICHARDSON ELECTRONICS
SENDER
Relationship with RICHARDSON ELECTRONICS
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 .

10. Near future projects FCC type acceptance.
SENDER
Near future projects
FCC type acceptance.
Frequency agile 1.5 KW transmitter.
IBOC compatibility.
Inboard audio processor and modulation monitor.
Higher power amplifiers

11. Reliability in A.M. stations
SENDER
Reliability in A.M. stations

12. Introduction Station Concept Harmonic set of: Transmitter
SENDER
Introduction
Station Concept
Harmonic set of:
Transmitter
Radiating system
Energy System
Auxiliary Equipment

13. Experience with stations using Solid State A.M. Transmitters
SENDER
Experience with stations using Solid State A.M. Transmitters
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

14. Basic elements of a station
SENDER
Basic elements of a station
ANTENNA
Audio &
Rem. Ctrl.
STL RX RF
H.V
TRANSF. TX
ATU
DISTR.
BOARD
T.P.
A.C.
GROUND PLANE

15. TRANSMITTER BASIC BLOCKS
SENDER
TRANSMITTER BASIC BLOCKS
POWER SUPPLY
PWM MODULATOR
R.F. DRIVER
CLASS D or E
R.F. OUTPUT FILTER
CONTROL,PROTECTIONS,SIGNALING
EXTERNAL INTERFACE

16. PWM MODULATOR GENERATES D.C + A.C. VOLTAGE FOR THE R.F. AMP.
SENDER
PWM MODULATOR
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.

17. PWM (PULSE WIDTH MODULATION)
SENDER
PWM (PULSE WIDTH MODULATION)
SIMPLIFIED DIAGRAM:
R.F.
AMPLIFIER
D.C. SUPPLY
Switch
(Mosfet)
PWM FILTER
LOAD

18. PWM BASIC OPERATION Between 1) y 4) duty cycle is increased
SENDER
PWM BASIC OPERATION
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
Filtered output voltage
PWM waveform 1) 2) 3) 4) S V RL

19. PWM Frequency spectrum
SENDER
PWM Frequency spectrum
Amplitude
D.C Component
PWM 0°
Audio
Frecuency
72 kHz
144 kHz

20. PWM Frequency spectrum
SENDER
PWM Frequency spectrum
Amplitude
D.C. component
PWM 180°
Audio
72 KHZ components out of phase
144 kHz
Frecuency
72 kHz

21. SENDER
PWM filter diagram

22. PWM filter frequency response
SENDER
PWM filter frequency response

23. PWM filter response sensibility to load changes
SENDER
PWM filter response sensibility to load changes
Rload +/- 15%

24. Load change consequences
SENDER
Load change consequences
With reduced load (Rload< Rnominal) transmitter will produce high frequency submodulation
With increased load (Rload>Rnominal) transmitter will show high frequency overmodulation
Distorsion will increase if filter is not propperly loaded.

25. Modulated class D R.F. Amplifier.
SENDER
Modulated class D R.F. Amplifier. +V T1 T3 RL T2 T4
PWM filter

26. Class D r.f. Amplifier diagram
SENDER
Class D r.f. Amplifier diagram

27. Class D Bridge parasitic elements
SENDER
Class D Bridge parasitic elements V+
Cds
Cgd
Cgs
Cds
Cgd
Cgs RL
Cds
Cgd
Cgs
Cds
Cgd
Cgs
Ciss = Cgs + Cgd
Crss = Cgd
Coss = Cds + Cgd

28. Mosfets drive Vgs Dead time V+ T1 T3 Vgs(thr) RL time T2 T4
SENDER
Mosfets drive
Vgs
Dead time V+ T1 T3
Vgs(thr) RL
time T2 T4
Vgs peak = 13V

29. R.F. drive circuit Ls and Cs series resonant
SENDER
R.F. drive circuit
Ls and Cs series resonant
Lp paralel resonant with mosfet input capacitance (Partially) Ls Cs
MOSFET drive
Drive signal Lp
SCgs

30. Class D bridge current paths
SENDER
Class D bridge current paths V+ T1 T2 RL T3 T4 V+ T1 T3 RL T2 T4

31. Class D bridge undisered current paths.
SENDER
Class D bridge undisered current paths. V+ V+ T1 T3 T1 T3 RL RL T2 T4 T2 T4

32. Class D Amplifier basics.
SENDER
Class D Amplifier basics.
Low impedance driver required for:
Fast switching
Low Vgs modulation by Crss
Tuned load to produce sinusoidal current
High efficiency (>95 %)
Duty cycle should be < 0.5
Avoid transversal currents
Coss charge and discharge through Rl

33. Class D R.F. Amp typical waveforms.
SENDER

34. MOSFET characteristics
SENDER
MOSFET characteristics
No secondary breakdown
positive temperature coeff. Of Rdson (Simplify parallel operation)
Voltage controled device (Vgs)
Driver impedance dependent switching times.
Intrinsic antiparallel diode

35. IRFP350 MOSFET Rdson = 0.3 ohms Vdss = 400 Vdc
SENDER
IRFP350 MOSFET
Rdson = 0.3 ohms
Vdss = 400 Vdc
Vgs = +/- 20 Vmax Vth = 3 V Vsat = 9 V
Id = 16 Tc=25ºC Tc=100ºC
Idmax = 64 A
f=1MHz, Vds=25V , Vgs=0V
Ciss = 2600 pF (2400 pF for Vds>40V)
Coss = 660 pF (200 pF for Vds>40V)
Crss = 250 pF (50 pF for Vds>40V)

36. Class D amplifier example
SENDER
Class D amplifier example
SENDER

37. Class D Simulation (1/2 bridge,Vmax<400x.75/2.5)
SENDER
Class D Simulation (1/2 bridge,Vmax<400x.75/2.5)
Operational data
RL = 15 ohms
Po = W
h = %
Transistor stresses
Vmax = 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

38. Class E Amplifier diagram
SENDER
Class E Amplifier diagram

39. Class E amplifier example
SENDER
Class E amplifier example

40. Class E amplifier basics.
SENDER
Class E amplifier basics.
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 (>95%)
if special high voltage transistors with low Rdson are used

41. Clase E Waveforms
SENDER

42. Clase E Simulation (Vmax<400x.75/2.5)
SENDER
Clase E Simulation (Vmax<400x.75/2.5)
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
L1=12.3uH L2=3.7uH
C1= 4.1nF C2=4.9nF
Operational Data
RL = 7.3 ohms
Po = W
h = %
Transistor stresses
Vmax = V
Imax = 9.84 A
Pdis = 6.55 W x2 (13.1 Wtotal)
*Simulated with HEPA Plus from Design Automation

43. Passband Output filter
SENDER
Passband Output filter
Reduce R.F. Harmonics
High third harmonic att > 80 dB
Medium second harmonic att. > 40 dB
Higher harmonics att > 70 dB
Permits impedance matching between amplifier and load.
Atenuates low frequency components (Lightning protection)

44. Output filter Design oriented to protect R.F.amplifier
SENDER
Output filter
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)

45. SENDER
Output filter diagram

46. Output filter frequency response
SENDER
Output filter frequency response

47. Real and imaginary part of filter input impedance
SENDER
Real and imaginary part of filter input impedance

48. Protections integrated in the output filter
SENDER
Protections integrated in the output filter
SENDER
SENDER

49. Posible Transmitter Agresions
SENDER
Posible Transmitter Agresions
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

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

51. Short antenna example 60 m tower operating at 700 kHz ZL = 8 - j160
SENDER
Short antenna example
60 m tower operating at 700 kHz
ZL = 8 - j160
Q = 20
Electrical length = 50.4º

52. Type T -90º Standard A.T.U. 4.55uH j20 40.9uH j180 Zin 50+j0 11.37nF
SENDER
Type T -90º Standard A.T.U.
4.55uH
j20
40.9uH
j180
Zin
50+j0
11.37nF
-j20 ZL
8-j160

53. A.T.U.Sensibility to antenna impedance changes
SENDER
A.T.U.Sensibility to antenna impedance changes
Change in XL (+/- 10 ohm=6%)
if ZL=8-j150 Zin=19.5-j24.4 SWR=3.26
if ZL=8-j160 Zin=50+J0 SWR=1
if Zl=8-J170 Zin=19.5+j24.4 SWR=3.26
Change in RL ( +/- 1 ohm =12.5%)
if ZL=7-j160 Zin=57.1+j0 SWR=1.14
if ZL=9-j160 Zin=44.4+j0 SWR=1.14
RL and XL simultaneous variation
if ZL=7-j150 Zin=18.8-j26.8 SWR=3.52
if ZL=7-j170 Zin=18.8+j26.8 SWR=3.52
if ZL=9-j150 Zin=19.9-j22 SWR=3.10
if ZL=9-j170 Zin=19.9+j22 SWR=3.10

54. Complex A.T.U. (dual T) ! -j44.9 j50.5 j5 j145 Zin 50+j0 ZL 8-j160
SENDER
Complex A.T.U. (dual T)
-j44.9
j50.5 j5
j145
Zin
50+j0 ZL
8-j160
20-J13
-j92.5
j37
-20°
20°
Variations in XL
if ZL=8-j150 Zin=50+j62.5 SWR=3.26
if ZL=8-j160 Zin=50+j0 SWR=1.00
if ZL=8-j170 Zin=50-j62.5 SWR=3.26 !
Note: SWR of 8+/-j10 refered to a 8+j0 is 3.26

55. Load ladder Extreme values for SWR 1:1.5, refered to 50 Ohm, are:
SENDER
Load ladder
RF amplifiers
50 Ohm Z1
Antenna 1
combiner
filter
A.T.U. Zn n
15 Ohm
Extreme values for SWR 1:1.5, refered to 50 Ohm, are:
33.3+j j0
50-j j20.4

56. Load variation effects
SENDER
Load variation effects
Class D amplifier

57. A.T.U. And amplifier stresses
SENDER
A.T.U. And amplifier stresses
A)ZL=50-J62.5
Eff=93.5% Po=4.5W Ip=15.5A
B) ZL=50+J62.5
Eff=90.9% Po=2.02W Ip=1A
C) ZL=19.5+J24.4
Eff=84% Po=44W Ip=105A
D)ZL=19.5+J24.4
Eff=93.8% Po=395W Ip=73.7A
20°+20°
90°

58. Class D waveforms
SENDER
Ro=15 VSWR=1:1

59. Class D waveforms
SENDER
Ro=15-j6.1 VSWR=1:1.5

60. Class D waveforms
SENDER
Ro=15+j6.1 VSWR=1:1.5

61. Class D waveforms
SENDER
Ro=22.5 VSWR=1:1.5

62. Class D waveforms
SENDER
Ro=10.0 VSWR=1:1.5

63. Atmospheric discharges
SENDER
Atmospheric discharges
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 time:40 useg to 50%

64. Criteria to minimize damages
SENDER
Criteria to minimize damages
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

65. Discharge probability function
SENDER
Discharge probability function
N = 15 L (C·H+h)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: C= L=50 H=100m h=120m
N = 12.7 discharges per year.

66. Discharge current circulation
SENDER
Discharge current circulation 17 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 15 13 14 12 11 5 6 16 8 7 10

67. Equipment Instalation
SENDER
Equipment Instalation
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

68. Ground system equivalent circuit
SENDER
Ground system equivalent circuit

69. Discharge voltages and currents
SENDER
Discharge voltages and currents

70. Interference 1.- Intermodulation products are generated
SENDER
Interference
1.- Intermodulation products are generated
2.- SWR protection is desensitized
3.- Dangerous voltages at the R.F. Amplifier and
output filter maybe generated.

71. Transmitter Protections
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Transmitter Protections
A.C.input
Overload
Short cicuit
Transients
Overvoltage
Undervoltage
Assimetry
D.C.supply
Failure
R.F.
Overcurrent
SWR
Phase
overpower
Transients
Internal
R.F. Drive Temperature
PLL

72. Factory tests to ensure transmitter reliability
SENDER
Factory tests to ensure transmitter reliability
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

73. Conclusions Reliability in a transmitting sytem is a function of:
SENDER
Conclusions
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

74. Conclusions High quality station engineering A.C. Transient protection
SENDER
Conclusions
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

75. Recomended instrumentation for test and adjustment
SENDER
Recomended instrumentation for test and adjustment
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)
R.F. generator (Delta RG3-A or similar)
2.2 Spectrum analyzer (HP 8553B or similar) or detector included in RG3-A

76. 2.3 An H.P. vector impedance meter
SENDER
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 50+J0 Ohm.
3.2 R.F. Ammeter (Delta TC-1 or similar)
or R.F. Wattmeter
4.- To measure frequency response and distortion:
4.1 General purpose oscilloscope, 2 channel 4.2 Audio analyzer (Audio precision Portable
One or similar)
4.3 Modulation monitor (H.P A or B , Belar AMM3, TFT 923 A.M. or similar.)

77. 5.1 Spectrum analyzer 100KHZ.to 50 MHZ or more
SENDER
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

78. 7.- To measure transmitter carrier frequency.
SENDER
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 True RMS digital multimeter, suitable to operate in high R.F. fields. (Our best experience is with Fuke Digital multimeters.)

79. 10.1 USASI Noise generator. (Delta SNG-1).
SENDER
10.- For long run test.
10.1 USASI Noise generator. (Delta SNG-1).

80. SENDER
SENDER
Pablo Phillips D.
Agosto 1999