Common Practices For Internal Options Board Design - Tait TM8000 Series Applications Manual

4.1.3

Common Practices for Internal Options Board Design

Thermal
Considerations
Sealing
Electromagnetic
Compatibility
Susceptibility to
Interference
Emissions from the
Internal Options
Board
90 Creating Your Own Options Board
Select components which withstand the temperatures inside the radio body,
in particular during high duty cycles and high ambient temperatures.
Tait recommends the use of industrial-grade components (<85°C).
Heat dissipation added by an internal options board can reduce the radio's
operating temperature range or duty cycle. Keep heat dissipation to a
minimum.
The IP54 protection class no longer applies when the external options
connector or an additional connector are used. When fitting one of these
connectors, it is the integrator's sole responsibility to provide adequate
sealing.
It is important that the internal options board is electro-magnetically
compatible (EMC) with the radio itself and the external environment.
This means that the internal options board is not affected by and does not
interfere with the radio or the external environment. An EMC problem has
three components: a source, a coupling mechanism and a receiver.
The coupling mechanism can be conducted and/or radiated.
Key things to consider are as follows:
If the internal options board has connections via the external options
connector and the radio's antenna is located close to the options cable,
significant RF pick up on to the cable may occur.
If the internal options board contains sensitive analogue circuits (particularly
microphone circuits), digital ground noise may be a problem if the internal
options board is not earthed correctly.
Electrostatic discharge (ESD) onto the options cable may cause damage to
the internal options board or malfunction if proper protection is not
provided.
The radio's receiver is extremely sensitive and radiation from the internal
options board on the desired channel frequency may cause interference.
If the internal options board has connections via the external options
connector and the radio's antenna is located close to the cable, radiation
from the cable may be picked by the antenna as interference.
Radiation from the options cable, if strong enough, may interfere with other
devices near the radio or cause failure to comply with EMC regulations in
your country or region. The cable creates a good antenna at high
frequencies.
Follow the guidelines in "Guidelines for EMC Design" on page
TM8000 3DK Hardware Developer's Kit Application Manual
September 2003 © Tait Electronics Ltd
91.