SparkFun Forums

[siegelj]

Hi,

I recently made a design with a GE864-GPS and foolishly assumed I could use the same antennas as the GM862 without additional work. The end result is that I had an on-board LNA, an active antenna, and no way to power said antenna.

I know I should be able to use a passive antenna since I can use my GSM antenna and get reasonably good signal), but I can't seem to find any decently priced passive GPS antennas with u.FL connectors. Does anyone have a suggestion? I'm looking for 100, and have been targeting $350USD total (since I shouldn't -really- need much more than a PCB antenna).

Thank you!

[michelebavaro]

Hi,

I found this one:
http://www.aldafunk.com/GPS-Antenna/Pas ... ::215.html
but the price is outside your range

My suggestion would be to just buy a 100 25x25 elements and produce a small interface PCB. I am not an expert, but I think that microstrip antennas would not be the best for GPS as it is better to have right-handed circular polarisation and spiral antennas tend to be quite big in standard dielectrics.
Or browse Alibaba and cross fingers.

Sorry,
Mic

[siegelj]

Thanks Mic,

I had a look at that one and Alibaba isn't turning up much other than pin-mount.

I do already have 100 active antennas here, but my board doesn't provide power to the antenna (and so I get no signal). Could I modify the u.fl connector to supply a voltage to the antenna easily? If it was one wire, I'd do it in a second - but if I have to build 100 setups with an inductor, a resistor, ... (as I think I would have to), it may be easier to continue the search than do all the rework.

[michelebavaro]

Well, the most basic bias tee you can build is 1 inductor and 1 capacitor.

The capacitor must block the DC from flowing back to the GPS module (LNA input), whilst the inductor (choosen with the appropriate value, self-resonant frequency, and quality factor) will block the RF from flowing into your power supply.
For GPS L1 values between 47nH and 82nH and between 100pF and 470pF are most common.
So if you already have a cap on the GPS line, just a simple inductor placed from VCC to the RF pad of the u.FL connector will do. It's nothing clever really.. I imagine that you already considered this option and discarded it...

[MichaelN]

I second Michele's suggestion of adding an inductor / capacitor to provide power. I've had to do this when I forgot to provide provision on the PCB. As Michele suggsets, make sure the self-resonant frequency of the inductor is well above that used by GPS (about 1500MHz).