Globalstar ST100 User Manual page 84

8545-0194-01 v1.0
16. Remove the u.FL / SMA adapter cable from the ST100 calibration board and connect it to the other ST100 board for
antenna tuning (NOTE: the other ST100 board will require a semi-rigid RF coax if J2 is not installed).
17. Once the u.FL/SMA adapter is connected to the other ST100 PCB, record the impedances of the 1575.42MHz and
1615MHz markers. This is the initial antenna impedance without tuning. You can also take a photo to have as a reference
for later.
18. When tuning a RF network, the goal is to get the impedance on the Smith Chart to move as close as possible to the center
of the Smith Chart circle. This is the 50 ohm point (50 +j0). Another good rule of thumb is to have a minimum of -10dB
return loss (S11) for all orientations of the antenna.
19. Once the initial impedances have been recorded, use a Smith Chart simulation tool to determine which components (i.e.
shunt inductor or series capacitor) should be added to move the impedance as close as possible to the Smith Chart center
point. (NOTE: Iowa Hills Smith Chart is a free tool that can be downloaded.)
20. The values from the simulation may not be exact, so you may have to experimentally solder the simulation values onto the
ST100 PCB, and check on the VNA if these values are getting the impedance closer to the center point.
NOTE: L21, L14, and L13 are the matching components that can be used. L13 can be used, but past experience shows
to start with using L21, and then L14. The components that Globalstar has used in the past have been Murata LQP03TN
inductors and Murata GJM15, 0402 HiQ, tight tolerance capacitors.
21. Once both 1575.42MHz and 1615MHz impedances are close to the center point and you have -10dB return loss for both
frequencies in all end-application orientations, the tuning can be stopped. Record the final tuning values.
22. Remove the 0402, 0 ohm resistor that was installed in step 7, and install a 0 ohm, 0402 on R16. The ST100 board with a
tuned antenna is now ready to be tested outdoors.
ST100 User Manual v1 Confidential & Proprietary Information 77