LimeSDR-USB as GPS receiver

#1

Hello Everyone,

I am trying to use LimeSDR-USB as a GPS receiver. To achieve this, I have an active GPS L1 antenna and a LimeSDR-USB. Now, I must give some power to the antenna to power up the LNAs inside.

For this I need a Bias T. Can someone please suggest me a suitable Bias T which is not so expensive and can work well in my case.

Thank You All,
Priyanka

#2

Hello Priyanka,

The LimeSDR-mini has an option to solder a bias inductor e.g. MN24 TDK 33nH 0402 on the Rx path. You then have to choose 3.3V or 5V bias with EITHER R21 (5.0V) 47R 0402, OR R20 (3.3V) 47R 0402. C21 100nF 0402.

But for other LimeSDRs…

Minicircuits sell a range of Bias Tees for around $60 each. e.g. ZFBT-4R2G+.

Otherwise it is very easy to make a Bias Tee, e.g. strip board, 2 SMA connectors, 10nF chip capacitor (RF path) and 33nH chip inductor (DC feed) on the active antenna side. I would normally fit 47R and x2 100nF on the non RF side of the inductor. One capacitor on the 47R-33nH junction, the other on the other side of the 47R. This RC filtering helps to reduce supply noise from linear voltage regulators.

Low cost active antennas for GPS typcially draw about 10mA.

If you need to choose a linear voltage regulator (LDO), the TI LP5900 and LP5907 are very low noise.

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#3

Thanks a lot Danny for you reply. This is really helpful.