User Manual
Transceiver Module TC695
Page 6 / 6
UM-TC695-V1-0.DOC [ Word 2000 ] sedh/dous
HBC-radiomatic GmbH • 74564 Crailsheim • Germany
2004-12-15
Information and specifications subject to change without notice.
www.hbc-radiomatic.com
2.3 Oscillator and frequency synthesizer
The VCO1 generates the first oscillator frequency with a power of about 0 dBm. With Q1
the signal is amplified to about 6dBm. A portion of the amplitude of the oscillator signal
is led back to the double synthesizer U8 via the voltage divider R29-R32 for reference
voltage formation. The synthesizer U8 is fed with 12.8 MHz via a highly stable (+-2ppm -
30/+70 deg. Celsius) clock source (TCXO1). The control voltage thus generated is led to
the oscillator VCO1 via the loop filter at the output of U8 (D01) and hence determines
the frequency stability of the VCO. The frequency setting is carried out with the help of
the microcontroller U14. The frequency data is read in via the lines DATA, CLOCK and
LE.
2.4 First IF 45 MHz
From the mixer output MI1 (IF), the input signal, which is now mixed to 45 MHz, passes
via the transmit-receive switch U6 into the first IF amplifier Q8 . The 4-pin quartz filter
XF2 located at the output of Q8 generates the channel selection with a bandwidth of
25kHz. The received signal then continues to the input of the 2
nd
mixer and the 2
nd
IF
preamplifier U12.
2.5 Second IF 455 kHz and RSSI
The received signal travels via the input RFin to the second mixer and is mixed with the
internal quartz oscillator XT4 44.545 MHz to the second IF of 455 kHz. Here the
receiving signal is further amplified and selected with 2 further band filters (FI5 and FI7).
The IF signal is demodulated with the demodulator circuit L10 and the integrated
quadrature demodulator and is then available as a LF signal and AFout of U12. At the
RSSIout output of U12 a voltage value RSSI (Radio Signal Strength Indicator) is issued,
similar to the input field strength, which goes into microprocessor U14 via RE2 for
further processing.
2.6 LF signal
After removing the HF residues (455 kHz) through a passive low-pass filter (R63, C132,
R51 and C115) the LF signal still travels through a digital low-pass filter to be amplified
again in U13. The max. LF pass frequency is 5 kHz. This LF output signal is now
available at Pin 18 (AF-out) on multipoint connector ST2 of the transceiver with an
adjustable voltage of 0.2 – 2 Volt (RE5).
3 Receiver 2 (scanner receiver):
3.1 The function of the 2
nd
receiver largely corresponds with that of receiver 1, 2.1-2.6,
with the difference that the second IF 21.4 MHz and the VCO2 frequency vary by the
difference of the 2
nd
IF above the input frequency. During reception, the second receiver
searches for the occupancy data of the frequencies. The 2
nd
receiver requires about 3
seconds for the process of scanning 67 frequencies. The field strength data for each
respective HF channel is issued via the Pin RSSIout, U11 for further processing on the
microprocessor. The field strength data on the frequencies is available via RS232 at St2
PIN 1 (TXD) for further processing (e.g. TC6X5 spectrum monitor)
