52
52
mosaic-H RF Gain Adjustment
52
Appendix C
mosaic-H RF Gain Adjustment
This appendix in only applicable to the dual-antenna mosaic-H module.
The pre-amplification in front of the mosaic-H is required to be between 15 and 35 dB
(AGC gain reported by the receiver between 30 and 50dB). This is net pre-amplification,
equal to the active gain of the antenna minus losses in the coax cables at 1.6 GHz. Above
35 dB of pre-amplification, the cross-talk of the auxiliary antenna into the main antenna
could degrade performance.
Applications which work with high gain antennas shall use in-line attenuators. These can
be implemented on the PCB as indicated in the figure below.
•
TVS diode: use SESD0402X1BN-0010-098 or equivalent
•
Inductor L: select an inductor which is self-resonant between 1350 and 1450
MHz, with at least 300 mA current rating, e.g. Würth 744786139A
•
Avoid stubs at the RF path. The inductors, TVS diodes and R1 resistors shall be
very close to the RF trace, and have short grounding if applicable.
If the target attenuation is A dB, the resistors R1 and R2 can be dimensioned as follows,
rounding to the nearest E12
3
value:
𝑅1 = 50.
1 + 10
−𝐴 20
⁄
1 − 10
−𝐴 20
⁄
𝑂ℎ𝑚
𝑅2 =
5000. 𝑅1
𝑅1
2
− 2500
𝑂ℎ𝑚
The table below shows R1 and R2 values for some common attenuations:
Attenuation [dB]
R1 [Ohm]
R2 [Ohm]
6
150
39
10
100
68
20
56
220
3
E12 series multipliers of a power of ten: 1.0, 1.2, 1.5, ,1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2
