Informações sobre o equipamento:

Aeroflex 2025 Gerador
Fabricante:
Aeroflex
Modelo: 2025
Data: 1999
Categoria: Instrumentos de medição
Grupo: Gerador
Descrição: AM/FM SIGNAL GENERATORS
Informações:
                                    Introduction
The 2023, 2023A, 2023B, 2024 and 2025 AM/FM Signal
Generators cover the following
frequency ranges:
9 kHz to 1.2 GHz 2023 and 2023A
9 kHz to 2.05 GHz 2023B
9 kHz to 2.4 GHz 2024
9 kHz to 2.51 GHz 2025
Output levels from -140 dBm to +13 dBm are available.
Factory fitted options are available to
extend the level to +25 dBm (+19 dBm above 1.2 GHz) and to
provide SINAD measurement
capability. Fig. 1-1 is a block diagram of the frequency
synthesis and signal processing circuits.
Synthesizer
A VCXO operating at 100 MHz is phase locked to the internal
(or external) frequency standard
using a phase comparator at 10 MHz. The VCXO signal is
divided by 20 to give a 5 MHz
reference frequency for the fractional-N loop phase comparator.
A fractional-N loop is used to lock a multiplied low-noise
VCO to the reference with a resolution
of l Hz. The VCO tunes from 400 to 535 MHz and is multiplied
by three, four or five to yield a
signal in the range 1.2 to 2.51 GHz. A high speed
programmable divider is used to divide the
multiplied VCO frequency down to 5 MHz and a phase
comparator compares this signal with the
reference derived from the VCXO. The output from the phase
comparator corrects the VCO
frequency. In order to provide the required division ratio,
the programmable divider is required to
act as a fractional divider. The fractional-N gate array
controls the division ratio of the
programmable divider. The variation of this division ratio
by the controller enables the loop to
lock, with non-integer division ratios, to the reference
with the resolution of 1 Hz without
introducing spurious signals.
FM is produced using a two-point modulation scheme. The FM
signal is inserted into the loop by
summing the FM signal with the VCO tune line to modulate the
VCO directly. Simultaneously,
the FM signal is fed to the fractional-N controller via a
1-bit oversampled A-D converter which
converts an analogue input into a bit stream of ‘1’s and
‘0’s. The controller uses this input to
modulate the division ratio in sympathy with the modulation.
This allows frequencies less than
the loop bandwidth, including DC, to modulate the output
frequency.
In order to maintain good FM performance of the two-point
modulation system, the VCO FM
tracking characteristics are required to be known. The
sensitivity of the FM system via the 1-bit
oversampled A-D converter is VCO independent and accurately
calibrated by a DC calibration
system. The VCO tracking is derived by an automatic FM
SELFCAL routine during calibration.
During an FM SELFCAL, the error signal on the tune line, for
a frequency near the loop
bandwidth, is monitored while varying the FM calibration
numbers, allowing the variation in VCO
sensitivities to be calibrated out. This will remove any
perturbation of FM flatness near the loop
bandwidth due to mismatch of two modulation paths.
RF processing
The VCO on board AA1 operates in the range 400 to 535 MHz
and feeds to a harmonic generator
whose 3rd, 4th and 5th harmonics are selected by
voltage-tuned band-pass filters to provide a
frequency in the range 1.2 to 2.4 GHz (2.51 GHz on board
AA1/1). To generate frequencies
below 1.2 GHz this signal is divided by factors of two to
produce frequencies in the range 10 MHz
to 1.2 GHz. A bank of switched half octave harmonic filters
follows which is used to reduce
unwanted harmonics at the output. Then the signal passes
through the amplitude modulator where
the output level envelope is controlled. The output from the
modulator is peak detected. For
frequencies less than 10 MHz the signal is mixed with an
input from the 100 MHz VCXO. The
resulting output in the frequency range 9 kHz to 2.4 or 2.51
GHz is fed from the output amplifier
to attenuator board AA2. For pulse operation the signal is
taken to the pulse modulator which
operates in the range 30 MHz to 2.51 GHz. Otherwise the
pulse modulator is bypassed and the
signal is fed to the output attenuator. This is controlled
by relays and provides attenuation in steps
of 11 dB up to 132 dB. The attenuator also includes an RPP
(Reverse Power Protection) system to
protect the instrument from accidental application of
reverse power.

LF processing
The LF processing all takes place on control board AB1 or
AB1/1, and may be conveniently
subdivided into the following major functional elements.
LF output
A DSP (Digital Signal Processor) is used to generate the
audio frequency signals used for internal
modulation. One output from the DSP is used to supply the
front panel LF OUTPUT socket.
For external modulation the signal applied to the EXT MOD
INPUT socket first passes through
AC/DC coupling selection and then can either be applied
directly or via an ALC (Automatic Level
Control) circuit to the audio multiplexers. The external
direct signal can also be summed with the
audio frequency from the DSP.
AM and level control
For amplitude modulation the modulation depth is set by a
12-bit A-D converter. A second A-D
converter is used to produce the ALC reference for the RF
board. Square law correction is applied
to both signals.
FM/ϕM
For frequency modulation the signal amplitude controls the
FM deviation. For phase modulation
the signal is passed through a differentiator circuit.

Estes manuais estão disponíveis para os equipamentos acima:

Tipo manual: Manual de serviço Aeroflex-8780-Manual-Page-1-Picture
Páginas: 315
Tamanho: 6.89 Mbytes (7229185 Bytes)
Idioma: Inglês
Revisão: 1
Manual-ID/Number: 46892/377
Data: 08 Março 1999
Qualidade: Documento eletrônico, digitalização, bem legível.
Envie data:
MD5: c4980ac32baafbf11177dd867edf9c83
Downloads: 334 desde 05 Fevereiro 2017
Informações:
Includes information on:
Option 1: No attenuator
Option 2: DC operation
Option 3: High power
Option 4: High stability frequency standard
Option 5: Rear panel connectors
Option 7: Fast pulse modulation
Option 10: 1 V peak mod input
Option 11: Fast pulse and high power
Option 12: SINAD

Intended audience
The book is intended for qualified service engineers and
assumes a knowledge of the instrument to
a level covered in:
Operating Manual 46882-225 for 2023 and 2024
Operating Manual 46882-373 for 2023A, 2023B and 2025.
Structure
Chapter 1 Technical description
This includes block diagrams and detailed board circuit
descriptions. The circuit
descriptions refer directly to the servicing diagrams
contained in Chapter 7.
Chapter 2 Maintenance
Refer to this chapter for board and unit access, service
policy and routine safety
testing and inspection.
Chapter 3 Adjustment procedures
Refer to this chapter for information on password use and
adjustment procedures.
Chapter 4 Initial repair
What to do if the instrument shows no signs of life.
Chapter 5 Fault diagnosis
Based on error message reports; narrows the search down to a
defined circuit area.
Chapter 6 Replaceable parts
Contains instrument and board component parts, and a section
on miscellaneous
mechanical parts.
Chapter 7 Servicing diagrams
Contains interconnection drawings, board circuits and
component layout
diagrams.
Associated publications
Refer to the relevant Operating Manual (part number
46882-225 for 2023 and 2024, part number
46882-373 for 2023A, 2023B and 2025) for an up-to-date list
of associated publications.
Aeroflex-8780-Manual-Page-1-Picture


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