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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.
7.2 Bluetooth Antenna tuning
1. The Bluetooth antenna may not need tuning (it will depend if the Bluetooth range is acceptable as is), but the
process is the same as tuning the GPS/Satellite antenna, with the exception the frequency markers in the VNA
will be changed to 2.402GHz, 2.44GHz, and 2.48GHz.
Use or disclosure of data contained on this sheet is subject to the restrictions in the Distribution Statements on the title page of this
06/18/20
GLOBALSTAR PROPRIETARY AND CONFIDENTIAL INFORMATION
document.
Subject to Change without Notice
P a g e | 86
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