AB02S bias t for active gps antenna

#1

Hi Heltec (and others),

I’m using a number of the AB02S boards and working through trying to find the ideal antenna. I’m trying to assess whether active gps antennas will actually work.

From what I have seen of the v1.1 schematic, it appears that there is either an error in the way bias t power is wired, or it was never intended to provide power for an active antenna. Either that or the schematic has the internal antenna and the U.FL connector back to front.

Either way can some one from heltec comment on the state of bias -t power on the AB02S?

AB

#2

As far as I know there is error on schematic. The descriptions of antennas are swapped.
E1 is the external U.FL connector and E2 is the internal antenna.

So there is bias power for external antenna through 82nH inductor and 10 ohm resistor.

I used external active GPS antenna with no modifications to the board and it worked fine.

#3

Thanks @crey, that’s the conclusion I’ve come to as well. I would have expected a DC blocking capacitor between the t and the air530 chip but maybe the chip has one in-built.

#4

I designed some GPS receivers using u-blox chips and they also don’t need blocking capacitors.
The passive power circuit was very similar.

#5

Thanks for spotting and reporting the swap of E1 and E2.

So the antennas can coexist on the board? is there any hardware modification you would advice for long term use?