Download JN3 Hardware User Guide

7.
RF Front End Design
The JN3 contains an integrated LNA and pre-select SAW filter. This allows the JN3 to work
well with a passive GPS antenna. If the antenna cannot be located near the JN3, then an active
antenna (that is, an antenna with a low noise amplifier built in) can be used. The following
items will be discussed in turn to assist in designing the “RF front end”.
1. RF signal requirements
2. GPS antenna polarization
3. GPS antenna gain
4. System noise floor
5. Active versus passive antenna
6. RF trace losses
7. Implications of the pre-select SAW filter
8. External LNA gain and Noise Figure
9. Powering the external LNA (active antenna)
10. RF interference
11. Shielding