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SENDER
SENDER S.A.
SENDER A.M. Transmitters
SENDER
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 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 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.
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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.
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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.
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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
A1
Synth
A2
Combiner
PWM
An
PWR
Supply
Control
Output
Filter
Out
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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 .
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Near future projects
• 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
SENDER
Introduction
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
• 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
ANTENNA
STL
RX
Audio &
Rem. Ctrl.
RF
H.V
TRANSF.
DISTR.
BOARD
TX
T.P.
ATU
A.C.
GROUND PLANE
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TRANSMITTER BASIC BLOCKS
•
•
•
•
•
•
•
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
• 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)
SIMPLIFIED DIAGRAM:
R.F.
AMPLIFIER
D.C. SUPPLY
Switch
(Mosfet)
PWM FILTER
LOAD
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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
PWM waveform
1)
S
V
2)
RL 3)
4)
Filtered output voltage
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PWM Frequency spectrum
Amplitude
D.C Component
PWM 0°
Audio
72 kHz
144 kHz
Frecuency
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PWM Frequency spectrum
Amplitude
D.C. component
PWM 180°
Audio
72 KHZ components out of phase
72 kHz
144 kHz
Frecuency
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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
Rload +/- 15%
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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.
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Modulated class D R.F. Amplifier.
+V
T1
T2
PWM filter
RL
T3
T4
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Class D r.f. Amplifier diagram
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Class D Bridge parasitic
elements
V+
Cgd
Cgd
Cds
Cgs
Cds
Cgs
RL
Cgd
Cgd
Cds
Cgs
Ciss = Cgs + Cgd
Cds
Cgs
Crss = Cgd
Coss = Cds + Cgd
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Mosfets drive
Vgs
V+
T1
RL
Dead
time
T3
Vgs(thr)
time
T2
T4
Vgs peak = 13V
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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
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Class D bridge current paths
V+
T1
T2
RL
V+
T3
T1
T4
T2
RL
T3
T4
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Class D bridge undisered current
paths.
V+
T1
T2
RL
V+
T3
T1
T4
T2
RL
T3
T4
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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
Class D R.F. Amp typical
waveforms.
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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
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IRFP350 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)
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Class D amplifier example
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Class D Simulation
(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
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Class E Amplifier diagram
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Class E amplifier example
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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
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Clase E Waveforms
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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 = 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
• 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)
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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)
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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
• 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
• Impedance change
– Low heigth antennas are particularly
unstable
• Restricted bandwidth
• Interference from other stations
• Discharges
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Short antenna example
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.
4.55uH 40.9uH
j180
j20
Zin
50+j0
11.37nF
-j20
ZL
8-j160
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A.T.U.Sensibility to antenna
impedance changes
Change in XL (+/- 10 ohm=6%)
if ZL=8-j150
Zin=19.5-j24.4
if ZL=8-j160
Zin=50+J0
if Zl=8-J170
Zin=19.5+j24.4
Change in RL ( +/- 1 ohm =12.5%)
if ZL=7-j160
Zin=57.1+j0
if ZL=9-j160
Zin=44.4+j0
RL and XL simultaneous variation
if ZL=7-j150
Zin=18.8-j26.8
if ZL=7-j170
Zin=18.8+j26.8
if ZL=9-j150
Zin=19.9-j22
if ZL=9-j170
Zin=19.9+j22
SWR=3.26
SWR=1
SWR=3.26
SWR=1.14
SWR=1.14
SWR=3.52
SWR=3.52
SWR=3.10
SWR=3.10
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Complex A.T.U. (dual T)
-j44.9
Zin
50+j0
-j92.5
j50.5
20-J13
-20°
Variations in XL
if ZL=8-j150
if ZL=8-j160
if ZL=8-j170
j5
j145
ZL
8-j160
j37
20°
Zin=50+j62.5
Zin=50+j0
Zin=50-j62.5
SWR=3.26
SWR=1.00
SWR=3.26
Note: SWR of 8+/-j10 refered to a 8+j0 is 3.26
!
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Load ladder
RF amplifiers
1
50 Ohm
Z1
combiner
n
filter
Antenna
A.T.U.
Zn
15 Ohm
Extreme values for SWR 1:1.5, refered to 50 Ohm, are:
33.3+j0
75.0+j0
50-j20.4
50+j20.4
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Load variation effects
Class D amplifier
Load
VSWR
 (%)
15
15-j6.1
15+j6.1
22.5
10.0
1
1.5
1.5
1.5
1.5
97.93
96.55
97.83
98.47
96.94
P (1/2
bridge)
132.36
151.92
93.00
96.08
165.02
Vmax (V)
Imax (A)
110.81
109.80
110.83
110.02
110.84
4.12
57.77
3.44
13.89
5.66
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A.T.U. And amplifier stresses
20°+20°
90°
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
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Class D waveforms
Ro=15
VSWR=1:1
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Class D waveforms
Ro=15-j6.1
VSWR=1:1.5
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Class D waveforms
Ro=15+j6.1
VSWR=1:1.5
Class D waveforms
Ro=22.5
VSWR=1:1.5
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Class D waveforms
Ro=10.0
VSWR=1:1.5
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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%
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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
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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=0.1 L=50 H=100m h=120m
N = 12.7 discharges per year.
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Discharge current
circulation
1. Strike
2. Antenna
3. Discharge through the antenna
4. Guy
5. Isolator
6. Spark gap
7. Ground rod
15
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
17
1
3
2
4
14
13
12
11
16
9
5
8
6
7
10
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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
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Ground system equivalent circuit
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Discharge voltages and currents
Interference
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
•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
• 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
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
• 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
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
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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 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.)
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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
True 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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Pablo Phillips D.
Agosto 1999