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Electronics => RF, Microwave, Ham Radio => Topic started by: man_marius on October 13, 2021, 01:10:39 pm

Title: Labsat 3 Wide band noise level GPS position
Post by: man_marius on October 13, 2021, 01:10:39 pm

Hi

I have a problem with a labsat,
I have a GPS receiver that I want to verify. I have a scenario on the labsat recorded. When I play this scenario for my DUT gps receiver, I do not get signal acquisition. I know the scenario I recorded is okay, because some time back I was able to get a PVT solution.

My speculations
After checking the datasheet of the labsat I was to see that they use 3 bit quantization (best case scenario). This raises the noise level by around 20dB. Reducing my SNR can this explain the acquisition problems?

Is there a why to improve the SNR with the Labsat?

One way of doing that will simulate the antenna patterns, is it possible to do with the Labsat?

Title: Re: Labsat 3 Wide band noise level GPS position
Post by: ConKbot on October 15, 2021, 08:45:49 pm

If you have a 20db receiver noise figure, and a 2db n.f. LNA, then you are going to need at least 24db of gain on your LNA before the system noise figure drops below 3db.

https://www.pasternack.com/t-calculator-noise-figure.aspx (https://www.pasternack.com/t-calculator-noise-figure.aspx)

Note that cable loss/passive splitters between the LNA and receiver(recorder in this case) count against your LNA gain. So make sure your (LNAgain)-(cable loss) figure is over 24db, preferably 30db.
Also, when you start throwing high gain preamps at things, you're going to want band limiting also, either in the antenna passband, or a dedicated filter. With 30dbm of gain at 1575, a cell phone at 1800 can drive an LNA non-linear pretty easily without a bit of pre-selection.