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5-10 5100 ES Series Portable Radio Service Manual
Circuit Description
5.3.1 Receiver
5.3.1.1
Front End Bandpass Filter
A varactor-tuned bandpass filter (including W3 and W4) is used in the front-end of the
receiver. This filter provides first-image rejection with minimal loss to provide the desired
level of receiver sensitivity. The front-end bandpass filter center frequency is tuned via
voltages from an 8-channel D/A converter. Ceramic resonators provide a high circuit Q
and lower loss than a fixed inductor. A back-to-back varactor diode configuration
increases the circuit's third-order intercept point.
5.3.1.2
Front End LNA and Bypass Switching
Low Noise Amplifier (LNA) U33 is critical in determining the overall noise figure of the
receiver. The RF2361 amplifier provides a good noise figure, gain, intercept point and
power consumption. RF switches U28 and U37 bypass the signal around the LNA when
required to increase the effective third-order intercept point and the interference rejection
capabilities of the receiver.
5.3.1.3
Post-LNA Bandpass Filters
Additional bandpass filters are used after the LNA. These filters are fixed-tuned since
varactor-tuned filters would have an excessive third-order intercept point. One filter bank
is tuned to the 700 MHz receive band and the other bank to the 800 MHz receive band. RF
switches U8 and U7 select the desired band. These filters have better selectivity and more
loss than the front-end filters, but the gain of the LNA minimizes the impact of the filter
loss on the receiver sensitivity.
5.3.1.4
Mixer and LO Filter
A double-balanced, low-level ADEX-10L mixer (MX1) with a LO drive of +4 dBm is
used for the first conversion. This mixer provides good dynamic range with 3 dB lower
LO drive than the more tradi7 dBm drive mixers. This provides power savings and
reduces conducted and radiated LO leakage from the receiver. A high-side mix is used for
the 700 MHz receive band and a low-side mix is used for the 800 MHz receive band. This
band plan reduces the tuning range requirements for the VCOs.
A LO filter (including W1 and W2) is used prior to LO port of the mixer to reduce the
effect of wideband noise from the LO synthesizer on the receiver sensitivity. This filter is
varactor-tuned with the center frequency tuned via a voltage from a D/A converter.
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Страница 70: ...6 2 5100 ES Series Portable Radio Service Manual January 2007 Alignment Procedure ...
Страница 74: ...7 4 5100 ES Series Portable Radio Service Manual January 2007 Troubleshooting ...
Страница 125: ...January 2007 5100 ES Series Portable Radio Service Manual 9 47 Parts List Figure 9 4 Front Housing Assembly Model III ...
Страница 126: ...January 2007 5100 ES Series Portable Radio Service Manual 9 48 Parts List Figure 9 5 Front Housing Assembly Model II ...
Страница 127: ...January 2007 5100 ES Series Portable Radio Service Manual 9 49 Parts List Figure 9 6 Front Housing Assembly Model I ...
Страница 132: ...January 2007 5100 ES Series Portable Radio Service Manual 9 54 Parts List Figure 9 11 Front Cover Assembly Model II III ...
Страница 133: ...January 2007 5100 ES Series Portable Radio Service Manual 9 55 Parts List Figure 9 12 Front Cover Assembly Model I ...
Страница 134: ...January 2007 5100 ES Series Portable Radio Service Manual 9 56 Parts List Figure 9 13 Front Cover Assembly Detail ...
Страница 180: ...10 46 5100 ES Series Portable Radio Service Manual January 2007 Schematic Diagrams and Component Layouts ...