Using active antennas with LimeSDR

Hi everyone,

I’ve recently taken the plunge and pledged/ordered for a LimeSDR (USB A). I’ve got many ideas in mind for projects to use this board for, and one that is at the top of the list is a GPS receiver. Thing is, a typical GPS antenna is an active antenna, so it needs power on the coax. I am aware that the LimeSDR does not include an internal “bias tee” for providing power to an antenna, so I’m looking into what options I have. I have seen the video by LimeMicro demonstrating using an active patch antenna for receiving GPS signals, and that clearly has a bias tee of some sort attached that is powered from J16 on the LimeSDR. Does anyone know where (from the UK) I could purchase a similar component to use for exactly the same purpose? My attempts at googling this have tended to only find commercial and military high end equipment, which is not what I’m looking for. Am I using the wrong terminology?

Thanks in advance.

P.S. The video in question: You can see the bias tee clearly at 0:24, with power coming off pins on the LimeSDR.

Welcome, @DylanEde!

Something like this should do the trick:

Hi @andrewback, thanks for the reply. I’ve seen that part before, but I have a feeling that it’s far too high end for what I need. My other concern is the price. I am under the impression that for basic uses a bias tee should not need to be that expensive. For example they’re often included as part of low end SDRs. You can see in the video I linked that the bias tee in use there is just a small PCB with two SMA connectors and a pair of wires going to the J16 pins. The product you’ve linked appears to be quite a bit larger, the DC port is yet another SMA connector and it’s in a machined metal case.

Here’s a DIY solution:

I’ll try and find out where we got the one used in the demo, in case it was cheaper than the one from Farnell.

Hey, @andrewback, thanks for that. I look forward to any further information about the one in the demo. I’ve seen that blog post before, but I’m hoping to find a reasonable off-the-shelf part before resorting to making it myself, as my confidence in my soldering skills is not particularly high and I don’t have an old hard drive lying around to salvage the components from. Hopefully that blog post shows however that bias tees do not need to be expensive.

They’re technically simple devices, but RF and in particular as you go up in frequency — e.g. case in point being GNSS — performance is more sensitive to layout/construction. So the price on that part from Farnell isn’t actually that much in the scheme of things. That said, there are probably cheaper options.

Get one of these:

Ebay # 262708770651

It is as simple as it gets with usb power :slight_smile:



Nice and cheap!

That looks ideal, thanks! I’ve ordered one.