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mosaic-H RF Gain Adjustment
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In case a 10-dB attenuator is inserted, the supported net pre-amplification range would
be 25-45 dB. If the design is intended for one particular target configuration, for instance
with 45 dB pre-amplification, it is recommended to optimize the attenuator towards a 25
dB net pre-amplification in front of the module. In the example of a 45 dB pre-
amplification, a 20 dB attenuation shall be targeted.
The difference in pre-amplification in front of the main and auxiliary inputs of the module
shall be less than 5 dB. Higher mismatch could induce cross-talk between the signals of
both antennas, which could get significant compared to typical errors induced by
reflections and antenna non-idealities. When using identical antennas for the main and
auxiliary input, differences between pre-amplification usually relate to differences in cable
lengths. For example, RG58 cable will typically have between 0.5 and 0.8 dB/m loss at the
GNSS operating frequencies (consider 1.6 GHz). Therefore, RG58 cable length differences
beyond 6 m could cause issues.
In applications with limited asymmetry between both pre-amplifications (<5 dB), it is
recommended to route the stronger signal to the main antenna input and the weaker
signal to the auxiliary antenna input of the module. The circuit in section 4.2.3.2 is then
sufficient.
In applications with a more substantial asymmetry, an attenuator circuit is to be inserted
to reduce the strongest signal to the level of the weaker one. An example is shown in the
figure below, in which case the strongest signal would be at the AUX connector. R1 and
R2 shall be dimensioned as explained earlier, targeting an attenuation equal to the
expected difference between the pre-amplifications.
