SENDER A.M. TransmittersSENDER A.M. Transmitters

SENDER S.A.SENDER

SENDER S.A.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.

SENDER

Product LineProduct Line 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

SENDER

Product highlightsProduct 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.

SENDER

Basic specificationsBasic 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.

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 15000 SS W=80 cm,H=181cm D=81 cM , 500 Kg.

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.

SENDER

Basic block diagramBasic block diagram

Synth

PWM

Combiner

An

A2

A1

OutputFilter

ControlPWRSupply

Out

SENDER

Relationship with Relationship with RICHARDSON ELECTRONICSRICHARDSON 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 .

SENDER

Near future projectsNear future projects

• FCC type acceptance.

• Frequency agile 1.5 KW transmitter.

• IBOC compatibility.

• Inboard audio processor and modulation monitor.

• Higher power amplifiers

SENDER

Reliability in A.M. stations

SENDER

IntroductionIntroduction

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

Station Concept

SENDER

Experience with stations using Solid Experience with stations using Solid State A.M. TransmittersState 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 stabilityInterference from nearby stations

Reliability is reduced in unprotected stations

SENDER

A.C.

Basic elements of a station Basic elements of a station

GROUND PLANE

ATUTX

STL RX

RF

Audio &Rem. Ctrl.

T.P.

H.V TRANSF.

DISTR.BOARD

ANTENNA

SENDER

TRANSMITTER BASIC BLOCKSTRANSMITTER BASIC BLOCKS

• POWER SUPPLY• PWM MODULATOR• R.F. DRIVER• CLASS D or E• R.F. OUTPUT FILTER• CONTROL,PROTECTIONS,SIGNALING• EXTERNAL INTERFACE

SENDER

PWM MODULATORPWM 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.

SENDER

PWM PWM (PULSE WIDTH MODULATION)(PULSE WIDTH MODULATION)

SIMPLIFIED DIAGRAM:

D.C. SUPPLY Switch(Mosfet) PWM FILTER LOAD

R.F. AMPLIFIER

SENDER

PWM BASIC OPERATIONPWM BASIC OPERATION

Filtered output voltagePWM waveform

1)

2)

3)

4)

S

V RL

• 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

SENDER

PWM Frequency spectrumPWM Frequency spectrum

72 kHz 144 kHz

D.C Component

Audio

Amplitude

Frecuency

PWM 0°

SENDER

PWM Frequency spectrumPWM Frequency spectrum

72 kHz144 kHz

D.C. component

Audio

Amplitude

Frecuency

72 KHZ components out of phase

PWM 180°

SENDER

PWM filter diagramPWM filter diagramSENDER

PWM filter frequency responsePWM filter frequency responseSENDER

PWM filter response sensibility PWM filter response sensibility to load changesto load changes

Rload +/- 15%

SENDER

Load change consequencesLoad 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.

SENDER

Modulated class D R.F. Amplifier.Modulated class D R.F. Amplifier.

T1

T2

RLT3

T4

PWM filter

+V

SENDER

Class D r.f. Amplifier diagramClass D r.f. Amplifier diagramSENDER

Class D Bridge parasitic Class D Bridge parasitic elementselements

RL

V+

CdsCdsCgd

Cgs

CdsCdsCgd

Cgs

Ciss = Cgs + Cgd Crss = Cgd Coss = Cds + Cgd

CdsCdsCgd

Cgs

CdsCdsCgd

Cgs

SENDER

Mosfets driveMosfets drive

T1

T2

RLT3

V+

Vgs(thr)

Vgs peak = 13V

Dead time

Vgs

timeT4

SENDER

R.F. drive circuitR.F. drive circuit

Cgs

Drive signalLs Cs

Lp

• Ls and Cs series resonant• Lp paralel resonant with mosfet input

capacitance (Partially)MOSFET drive

SENDER

Class D bridge current pathsClass D bridge current paths

T1

T2

RLT3

T4

V+

T1

T2

RLT3

T4

V+

SENDER

Class D bridge undisered current Class D bridge undisered current paths.paths.

T1

T2

RLT3T3

T4T4

V+V+

T1T1

T2T2

RLT3

T4

V+V+

SENDER

Class D Amplifier basics.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

SENDER

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

SENDER

MOSFET characteristicsMOSFET characteristics

• No secondary breakdown• positive temperature coeff. Of Rdson

(Simplify parallel operation)• Voltage controled device (Vgs)• Driver impedance dependent switching

times.• Intrinsic antiparallel diode

SENDER

IRFP350 MOSFETIRFP350 MOSFET

• Rdson = 0.3 ohms• Vdss = 400 Vdc• Vgs = +/- 20 Vmax Vth = 3 V Vsat = 9 V• Id = 16 A @ Tc=25ºC 10 A @ Tc=100ºC• Idmax = 64 A• Capacitance @ 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)

SENDER

Class D amplifier exampleClass D amplifier example

SENDER

SENDER

Class D SimulationClass D Simulation(1/2 bridge,Vmax<400x.75/2.5)(1/2 bridge,Vmax<400x.75/2.5)

• 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

• 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)

*Simulated with HB plusfrom Design Automation

SENDER

Class E Amplifier diagramClass E Amplifier diagramSENDER

Class E amplifier exampleClass E amplifier exampleSENDER

Class E amplifier basics.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

SENDER

Clase E WaveformsClase E WaveformsSENDER

Clase E SimulationClase E Simulation(Vmax<400x.75/2.5)(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 = 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

SENDER

Passband Output filterPassband 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)

SENDER

Output filterOutput 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)

SENDER

Output filter diagramOutput filter diagramSENDER

Output filter frequency responseOutput filter frequency responseSENDER

Real and imaginary part of filter Real and imaginary part of filter input impedanceinput impedance

SENDER

Protections integrated in the Protections integrated in the output filteroutput filter

SENDER

SENDER

SENDER

Posible Transmitter AgresionsPosible 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

SENDER

Antenna related problemsAntenna related problems

• Impedance change– Low heigth antennas are particularly

unstable• Restricted bandwidth• Interference from other stations• Discharges

SENDER

Short antenna exampleShort antenna example

60 m tower operating at 700 kHz

ZL = 8 - j160Q = 20Electrical length = 50.4º

SENDER

Type T -90º Standard A.T.U.Type T -90º Standard A.T.U.

4.55uHj20

40.9uHj180

ZL8-j160

11.37nF-j20

Zin50+j0

SENDER

A.T.U.Sensibility to antenna A.T.U.Sensibility to antenna impedance changesimpedance changes

Change in XL (+/- 10 ohm=6%)if ZL=8-j150 Zin=19.5-j24.4 SWR=3.26if ZL=8-j160 Zin=50+J0 SWR=1if 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=1.14if ZL=9-j160 Zin=44.4+j0 SWR=1.14RL and XL simultaneous variationif ZL=7-j150 Zin=18.8-j26.8 SWR=3.52if ZL=7-j170 Zin=18.8+j26.8 SWR=3.52if ZL=9-j150 Zin=19.9-j22 SWR=3.10if ZL=9-j170 Zin=19.9+j22 SWR=3.10

SENDER

Complex A.T.U. (dual T)Complex A.T.U. (dual T)

j5 j145

ZL8-j160j37

Zin50+j0

j50.5

-j92.5

-j44.9

Variations in XLif ZL=8-j150 Zin=50+j62.5 SWR=3.26if ZL=8-j160 Zin=50+j0 SWR=1.00if ZL=8-j170 Zin=50-j62.5 SWR=3.26

Note: SWR of 8+/-j10 refered to a 8+j0 is 3.26 !

20°-20°

20-J13

SENDER

Load ladderLoad ladder

RF amplifiers

Zn

Z1

Extreme values for SWR 1:1.5, refered to 50 Ohm, are:33.3+j0 75.0+j050-j20.4 50+j20.4

1

n

combiner filter A.T.U.

Antenna50 Ohm

15 Ohm

SENDER

Load variation effectsLoad variation effects

Class D amplifierClass D amplifier

Load VSWR (%) P (1/2bridge)

Vmax (V) Imax (A)

15 1 97.93 132.36 110.81 4.1215-j6.1 1.5 96.55 151.92 109.80 57.7715+j6.1 1.5 97.83 93.00 110.83 3.44

22.5 1.5 98.47 96.08 110.02 13.8910.0 1.5 96.94 165.02 110.84 5.66

SENDER

A.T.U. And amplifier stressesA.T.U. And amplifier stresses

A)ZL=50-J62.5Eff=93.5% Po=4.5W Ip=15.5A

B) ZL=50+J62.5Eff=90.9% Po=2.02W Ip=1A

C) ZL=19.5+J24.4Eff=84% Po=44W Ip=105A

D)ZL=19.5+J24.4Eff=93.8% Po=395W Ip=73.7A

90°

20°+20°

SENDER

Class D waveformsClass D waveformsRo=15 VSWR=1:1

SENDER

Class D waveformsClass D waveformsRo=15-j6.1 VSWR=1:1.5

SENDER

Class D waveformsClass D waveformsRo=15+j6.1 VSWR=1:1.5

SENDER

Class D waveformsClass D waveforms

Ro=22.5 VSWR=1:1.5

SENDER

Class D waveformsClass D waveformsRo=10.0 VSWR=1:1.5

SENDER

Atmospheric dischargesAtmospheric discharges

• At the antenna• In A.C.lines• In telephone lines

Characteristics

Imax: 200 kA Itypical: 10 a 20 kAdI/dT typical: 10 kA/usegRisetime: 2 useg Decay time:40 useg to 50%

SENDER

Criteria to minimize damagesCriteria 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

SENDER

Discharge probability functionDischarge probability function

N = 15 L (C·H+h)2 ·10-6

N = Discharges per yearL = 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=0.1 L=50 H=100m h=120mN = 12.7 discharges per year.

SENDER

Discharge current Discharge current circulationcirculation

1

14

107

2

5

3

8 611

4

13 1215 9

16

17

1. Strike 2. Antenna 3. Discharge through the antenna 4. Guy 5. Isolator 6. Spark gap 7. Ground rod 8. Base insulator 9. Cnecting Loop11. A.T.U. isolator12. A.T.U.13. Ferrite core14. Coaxial cable15. Discharge current in caxial cable16. A.T.U. Spark gap17. Disipator

SENDER

Equipment InstalationEquipment Instalation

A.C. Line transient protector

Panelboard

Coaxial cable

Building ground

Ferrite toroids

Transmitter A.C. line

A.C. mains

Reference ground

Ground to auxiliary

equipment

SENDER

Ground system equivalent circuitGround system equivalent circuitSENDER

Discharge voltages and currentsDischarge voltages and currentsSENDER

InterferenceInterference

1.- Intermodulation products are generated

2.- SWR protection is desensitized

3.- Dangerous voltages at the R.F. Amplifier and output filter maybe generated.

SENDER

Transmitter ProtectionsTransmitter Protections

•A.C.inputOverloadShort cicuitTransientsOvervoltageUndervoltageAssimetry

•D.C.supplyOverloadTransientsFailure

• R.F.OvercurrentSWRPhaseoverpowerTransients

• Internal R.F. Drive TemperaturePLL

SENDER

Factory tests to ensure transmitter Factory tests to ensure transmitter reliabilityreliability

• 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

SENDER

ConclusionsConclusions

• Transmitter intrinsic reliability– Power stages regimes much lower than devices

limits– Simple low power stages with low number of

components

• Rational protections adjustment

Reliability in a transmitting sytem is a function of:

SENDER

ConclusionsConclusions

• 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

SENDER

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

SENDER

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. 8901 A or B , Belar

AMM3, TFT 923 A.M. or similar.)

2.3 An H.P. vector impedance meter may be used instead of 2.1,2.2 and 2.3

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

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.)

SENDER

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

SENDER

SENDERSENDER

Pablo Phillips D.Agosto 1999

SENDER