52
Reciter Circuit Description
TB8100 Service Manual
© Tait Electronics Limited September 2006
Modulation Based
on Varicap Diodes
Modulation on the VCO is provided by an auxiliary varicap-based control
circuit which provides a modulation gain of 5kHz/V
p
.
Low Noise Amplifier
A BJT cascode amplifier is used as a broad band isolator and low noise
amplifier. This has internal self-bias circuitry, and the output provides
enough RF power to drive the following stages.
Harmonic Filter
The VCO has a relatively high harmonic content. A third order low pass
elliptic filter is used to attenuate this content.
Fixed Slope
Attenuator, Final
Driver and Fixed
Attenuator
A silicon BJT is used as a broad band matched Class A final driver to drive
the +20dBm local oscillator port of the mixer. To maintain a fixed output
level, a fixed slope attenuator is introduced at the input to the final driver so
that the attenuation rate (slope) increases with an increase in frequency. A
fixed attenuator provides a signal level of +11dBm
±
2dB to the input port
of the PA, providing better reverse isolation.
The B-band VCO frequency spans from either 136MHz to 156MHz, or
148MHz to 174MHz, according to the product type.
The C-band VCO frequency spans from either 174MHz to 193MHz, or
193MHz to 225MHz, according to the product type.
Refer to
“Identifying the Reciter” on page 70
for more information on
reciter product types.
2.5.4
VCO - UHF Reciter
The exciter VCO consists of a high Q VCO, modulation based on varicap
diodes, low noise amplifier, harmonic filter, fixed slope attenuator, final
driver and a fixed attenuator.
Note that the K-band reciter uses two VCOs (refer to
), with the appropriate VCO stage being selected for operation
according to the frequency of the channel in use. Only one VCO can be
operational at any one time.
High Q VCO
The VCO BJT transistor operates in a common collector, Colpitts oscillator
configuration, and uses a shorted quarter-wave ceramic coaxial resonator.
The open end of the resonator is terminated by a combination of a high Q
trimmer and varactor diodes. This forms a high Q resonator which is both
mechanically and electronically tunable. Mechanical tuning is possible by
adjusting the trimmer. Changes in the control voltage from the loop filter
are applied to the varactors to facilitate electronic tuning.
Содержание TB8100
Страница 1: ...TB8100 base station Service Manual MBA 00016 02 Issue 2 September 2006...
Страница 8: ...8 TB8100 Service Manual Tait Electronics Limited September 2006 19 Subrack Servicing 287 Glossary 295...
Страница 62: ...62 Reciter Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 64: ...64 Reciter Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 66: ...66 Reciter Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 68: ...68 Reciter Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 98: ...98 Reciter Fault Finding TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 108: ...108 Reciter Board Replacement TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 110: ...110 Reciter Spare Parts TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 112: ...112 Reciter Spare Parts TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 124: ...124 Power Amplifier Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 126: ...126 Power Amplifier Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 172: ...172 Power Amplifier Fault Finding TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 178: ...178 Power Amplifier Disassembly and Reassembly TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 200: ...200 Power Amplifier Spare Parts TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 212: ...212 Power Management Unit Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 214: ...214 Power Management Unit Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 248: ...248 Power Management Unit Fault Finding TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 268: ...268 Power Management Unit Spare Parts TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 276: ...276 Control Panel Circuit Description TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 288: ...288 Subrack Servicing TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 294: ...294 Subrack Servicing TB8100 Service Manual Tait Electronics Limited September 2006...
Страница 306: ...306 TB8100 Service Manual Tait Electronics Limited September 2006...