Cinterion
®
EMS31-US Hardware Interface Overview
2.2 RF Antenna Interface
17
EMS31_US_HIO_v00.103
2017-11-27
Confidential / Preliminary
Page 14 of 33
2.1.5
Control Signals
2.1.5.1
Status LED
Note that this feature is not available with release 1.
The LED line can also be configured as GPO5 line, and can be used to drive a status LED that
indicates different operating modes of the module (for GPOs see
Section 2.1.4
). LED and
GPIO5 functionality are mutually exclusive.
2.2
RF Antenna Interface
The RF interface has an impedance of 50
Ω
. EMS31-US is capable of sustaining a 10:1 voltage
standing wave ratio (VSWR) mismatch at the antenna line without any damage, even when
transmitting at maximum RF power.
The external antenna must be matched properly to achieve best performance regarding radi-
ated power, modulation accuracy and harmonic suppression. Antenna matching networks are
not included on the EMS31-US module and should be placed in the host application if the an-
tenna does not have an impedance of 50
Ω
.
Regarding the return loss EMS31-US provides the following values in the active band:
Table 3:
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
