As I am sure you are aware, the impedance of this type of antenna is highly dependent on the ground plane used with the antenna,? When I measured the antennas using my HP8753C VNA, I found they were only resonant as specified when mounted over a large copper ground plane.? As used in SHARI (and HT 's in general), where the ground plane consists of the case and the shield of the SA818 and the antenna can be adjacent to numerous other conductive surfaces, it is not possible to maintain a low VSWR.??
The SA818 module was designed by niceRF for use as the RF module in an HT using a rubber duck antenna.? They call it the " NiceRF SA818 1W Embedded walkie talkie module" so we know that it has been designed for use with a rubber ducky antenna with an uncontrolled impedance.? For a greater safety margin, SHARI is wired to operate at the low power setting of 1/2 watt.
Steve - N8AR
Steve-N8AR