ABACOM Technologies TX-FM Manuel de démarrage rapide - Page 2

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Block Diagram and Pin-Out
LF Section and Modulator
The Low Frequency section consists of two AC-coupled amplifiers with voltage gains of: AMP 1 = 20 and
AMP 2 = 5 and have a LF bandwidth of 20 Hz to 30KHz.
The FM modulator is an oscillator stabilized by means a SAW resonator and modulated by a varicap
diode. This can be driven by a signal having a maximum peak-to-peak voltage (V
the maximum V
that can be input to the AMP 2 (pin 7) is 10V/ 5 = 2V.
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In a configuration where the two stages, AMP 1 and AMP 2, are directly connected to each other (by short-
circuiting pin 6 with pin 7) in order to amplify the LF input signal as much as possible, the max V
may be applied to pin 4 is 10V: (5 x 20) = 100 mV.
Pre-emphasis Network
In order to improve the signal-to-noise ratio and the dynamics of the demodulated signal (see RX-FM
AUDIO application note) it's advisable to fit a pre-emphasis network in between the 1
stages.
The pre-emphasis network shown above, lowers the bass tones by about 6 times with respect to the
trebles, makes the FM modulation index approximately constant over all the audio bandwidth and
increases the available dynamics for the bass tones.
Even if the pre-emphasis network is used, the max V
TX-Enable
Pin 2 makes it possible to enable or disable the FM transmitter simply by interfacing it with TTL or CMOS
logic families supplying output logic levels of 0 to 5V and 0 to 12V respectively
To ensure the FM transmitter module switchoff, the low level driving signal on pin 2 should be a 0V logic
level of below 0.5V
The maximum Off/On switching-time is about 100µs.
RF Output
Three types of integral antenna are recommended for use with our RF modules and are descibed as
follows:-
• •
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that can be input to pin 4 remains 100 mV.
pp
ABACOM Technologies
1)
+12V
2)
TX enable (5 to 12V)
3)
Ground
4)
Input 1 (LF)
5)
Ground
6)
Output 1 (LF)
7)
Input 2 (LF)
9)
Ground
13)
Ground
15)
RF output
16)
Ground
) of 10V and, therefore,
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that
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st
nd
and 2
LF amplifier
2