User's Manual

RF Integration
Rev 3.0.3 Mar.12 Proprietary and Confidential 15
Developing custom antennas
Consider the following points when developing custom-designed antennas:
• A skilled RF engineer should do the development to ensure that the RF
performance is maintained.
• Identify the bands that need to be supported.
Determining the antenna’s location
Consider the following points when deciding where to put the antenna:
• Antenna location may affect RF performance. Although the module is
shielded to prevent interference in most applications, the placement of the
antenna is still very important—if the host device is insufficiently shielded,
high levels of broadband or spurious noise can degrade the module’s perfor-
mance.
• Connecting cables between the module and the antenna must have 50 
impedance. If the impedance of the module is mismatched, RF performance
is reduced significantly.
• Antenna cables should be routed, if possible, away from noise sources
(switching power supplies, LCD assemblies, etc.). If the cables are near the
noise sources, the noise may be coupled into the RF cable and into the
antenna.
Note: The MC7750 is
based on ZIF (Zero Inter-
mediate Frequency)
technologies. When
performing EMC (Electro-
magnetic Compatibility)
tests, there are no IF
(Intermediate Frequency)
components from the
module to consider.
Interference and sensitivity
Several sources of interference can affect the RF performance of the module
(RF desense). Common sources include power supply noise and device-
generated RF.
RF desense can be addressed through a combination of mitigation techniques
and radiated sensitivity measurement.
Power supply noise
Noise in the power supply can lead to noise in the RF signal.
Note: Values in this guide
are taken from the
MC7750 product technical
specification (PTS) —in
the case of a discrepancy
between this document
and the PTS, use the value
listed in the PTS.
The power supply ripple limit for the module is no more than 200 mVp-p 1 Hz to
100 kHz. This limit includes voltage ripple due to transmitter burst activity.
Interference from other wireless devices
Wireless devices operating inside the host device can cause interference that
affects the module.
To determine the most suitable locations for antennas on your host device,
evaluate each wireless device’s radio system, considering the following:
• Any harmonics, sub-harmonics, or cross-products of signals generated by
wireless devices that fall in the module’s Rx range may cause spurious
response, resulting in decreased Rx performance.