User's Manual Part 1

MC75 Hardware Interface Description

Strictly confidential / Draft

MC75_V00.190a Page 58 of 91 15.02.2005

4 Antenna Interface

The RF interface has an impedance of 50. MC75 is capable of sustaining a total mismatch

at the antenna connector or pad without any damage, even when transmitting at maximum

RF power.

The external antenna must be matched properly to achieve best performance regarding

radiated power, DC-power consumption, modulation accuracy and harmonic suppression.

Matching networks are not included on the MC75 PCB and should be placed in the host

application.

Regarding the return loss MC75 provides the following values in the active band:

Table 10: Return loss in the active band

State of module Return loss of module Recommended return loss of application

Receive > 8dB > 12dB

Transmit not applicable > 12dB

Idle < 5dB not applicable

The connection of the antenna or other equipment must be decoupled from DC voltage. This

is necessary because the antenna connector is DC coupled to ground via an inductor for

ESD protection.

4.1 Antenna Installation

To suit the physical design of individual applications MC75 offers two alternative approaches

to connecting the antenna:

• Recommended approach: U.FL-R-SMT antenna connector from Hirose assembled on

the component side of the PCB (top view on MC75). See Section 4.3 for details.

• Antenna pad and grounding plane placed on the bottom side. See Section 4.2.

The U.FL-R-SMT connector has been chosen as antenna reference point (ARP) for the

Siemens reference equipment submitted to type approve MC75. All RF data specified

throughout this manual are related to the ARP. For compliance with the test results of the

Siemens type approval you are advised to give priority to the connector, rather than using the

antenna pad.

IMPORTANT: Both solutions can only be applied alternatively. This means, whenever an

antenna is plugged to the Hirose connector, the pad must not be used. Vice versa, if the

antenna is connected to the pad, then the Hirose connector must be left empty.