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I'm utilizing the RF module A7672A for GNSS positioning, aiming to identify the optimal antenna configuration to achieve the shortest TTFF in a compact PCB design, preferably using an SMT antenna. Based on my current tests:

Ceramic patch active antennas, such as ACTPAT182-01-IP, yielded a TTFF of 1 minute and 15 seconds. Ignion Dual band antenna with matching circuit (NN03-320) resulted in a TTFF of 3 minutes. Tilt antenna (YEGT001AA) also had a TTFF of 3 minutes. Now, I have a few questions:

Active or Passive Mode: For a compact design, is it more advantageous to operate the Sim A7672E module in active or passive mode?

Circuit Optimization: What components or circuitry between the module and the antenna can be added to optimize performance?

Antenna Types: Considering the goal of minimizing TTFF and maintaining a compact design, what type of antennas would be most suitable for this application?

Thank you for your help A7672 GNSS datasheet enter image description here

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  • \$\begingroup\$ Are you interested in cold or warm acquisition times, does the unit have battery backup for an RTC/almanac, if no battery backup can you set the RTC at startup, do you have the option of using AGPS? All of these factors can make a major difference to timings. \$\endgroup\$
    – colintd
    Jan 3 at 12:15
  • \$\begingroup\$ An active ceramic patch will always be best, but your small antennas sound terrible. Almost certainly something else is wrong. First, is the module compatible with a passive antenna? Does it need an external filter? Second, they're likely mismatched or mis-tuned. Do you have a NanoVNA? \$\endgroup\$
    – tomnexus
    Jan 3 at 22:20

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The biggest improvements will not come from the antenna (though that is important), rather you need to focus on providing a current RTC, a current Almanac, and if possible ephemerides and an approximate position. Taken together, these will all drastically reduce startup time.

Therefore look at options for battery backup of the module for RTC and Almanac (if not preserved in flash), or whether you can provide this information and more as part of your device startup sequence. Grouped under the title "Assisted GPS" or "AGPS", the use of these techniques is why mobile phones can lock on the GPS so quickly.

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  • \$\begingroup\$ So it is more on software optimization rather than hardware \$\endgroup\$ Jan 3 at 14:07
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    \$\begingroup\$ If your MPU has access to RTC and can obtain the almanac and ephemerides, then yes it is a software optimization. With good AGPS data you are much closer to warm restart than cold, and it can make an absolutely massive difference. Without that data, the GPS unit has to do a very wide range search across all possible satellites and transit times to get to first signal, and then wait until it has received the full almanac and ephemerides. Only then can it give you an accurate position. AGPS removes that long wait. \$\endgroup\$
    – colintd
    Jan 3 at 20:15
  • \$\begingroup\$ No, this was an antenna improvement question, and one way, the only simple way, of comparing antennas is TTFF. Of course backup power, RTC, Ephem, AssistNow, etc would help, but they don't improve the antenna. Why not just use Cell Locate or Wifi scanning or have the user type in their address? \$\endgroup\$
    – tomnexus
    Jan 3 at 22:17

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