Many vendors provide positioning modules that support active antennas as well as ones that don't. I am using 4 positioning modules out of which 3 of them support active antennas and the other , CC4000 by TI , supports only passive antennas. To be honest I am testing modules for performance, in terms of TTFF for SGEE, CGEE and A-GPS.
Take a look if its necessary.
http://www.u-blox.com/en/gps-modules/pvt-modules/max-m8-series-concurrent-gnss-modules.html
https://www.linxtechnologies.com/en/products/gps-modules/fm-gps-receiver-module
http://www.ti.com/tool/cc4000gpsem
However all three claim to have almost same acquisition gains,about 143 dBi.
But let me make my question general so that it will help more people.
For all 4 positioning modules that claim to have almost same acquisition gains, how would the antenna type (active/passive) effect its performance? I mean with a passive antenna if the module can have a acquisition gain of 143dBi why bother fixing it an active antenna?
Is an active antenna necessary for applications that have really short antenna cables(about 2-3cm)?
If I have gone wrong somewhere, kindly direct me.
Best Answer
Active antennas contain a low noise amplifier and possibly a filter and line driver. It is very important to put the LNA as close to the antenna as possible to get some gain before the cable loss. The trick with GPS is that the signal is extremely small. The GPS signal is actually below the noise floor of the LNA, so adding more gain really does not help at all above mitigating the loss in the cable. What does help is the coding gain in the receiver when it despreads the signal. This does not depend on the receiver as the coding gain is dependent on the design of the code.