Philips 50 T Series, Руководство по обслуживанию

Страница: 83 / 105

Transmitter Functional Blocks
Chapter 9 - Theory of Operation
EEPROM
The EEPROM holds the following settings:
• Serial number
• Gain calibration factors
• Country code
• Japanese ID code
Japan ID
This module is only acitve for Japanese options (set by the country code). It
sends the required ID code for Japanese Telemetry Transmitters. If there is
no valid ID code (or country code) in the EEPROM, this module shuts off
the VCXO. RF emission is allowed only if a correct ID code is emitted first
after power up.
VCXO
The Voltage Controlled Xtal (crystal) Oscillator is a "MAGIC" M1400-
6XXXX type VCXO. It generates the 4mW, 2mW or 1mW RF carrier in the
406 to 470 MHz band. This is dependant on county options:
• 4 mW for USA and Australia
• 2 mW for Europe
• 1 mw for Japan
It also performs the FM modulation for this carrier with the composite signal
of the ultasound doppler or the fetal scalp ECG and the FSK subcarrier for
the digital information. The heart rate signals use 60% and the FSK
subcarrier uses 40%of the available RF peak deviation. An additional lowpass
filter at the VCXO's output reducers the RF carrier harmonics.
The outer shield of the heart rate transducer cables is used as an antenna. An
impedence matching network adapts the antenna impedance to the VCXO's
50 Ohms output.