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Re: [Paparazzi-devel] STM32 and GPS receive

From: Stephen Dwyer
Subject: Re: [Paparazzi-devel] STM32 and GPS receive
Date: Thu, 13 Dec 2012 15:23:13 -0700


I was experiencing some issues with a LEA-5H with a helical antenna, (not locking, low signals), and so in light of this discussion we tried to take a very rough look at whether lisa/m v2 was generating any major noise. Using an agilent spectrum analyzer and a crappy dipole antenna, we did not see any extra noise or signal from Lisa/M v2.0 beyond the existing noise floor, with the exception of extremely intermittent and non-reproducible spikes, of which a few were generated during testing. These usually occurred when we plugged in the system, and generated a spark from the battery. Otherwise, noise and spikes were probably from whatever random RFI was floating around our lab (could have been anything, tons of machine shop and test equipment in our building, no good test location).

We are definitely familiar with GPS interference from processors. A few years ago we used a Geode based SBC running at 500MHz, it was awful. Huge spikes right around 1500-1600MHz (nice harmonic of 500). We couldn't get a GPS lock within a metre of the computer.

If anyone is interested, I have a few screenshots from the testing. Let me know and I will post them somewhere.

-Stephen Dwyer

On Mon, Nov 19, 2012 at 7:43 AM, Christophe De Wagter <address@hidden> wrote:
Thank you for this throughout and interesing research.


On Sat, Nov 17, 2012 at 3:06 PM, Sergey Krukowski <address@hidden> wrote:
I tried any possible power supply configurations to be sure that the internal switching regulator does not affect this. And it is absolutely unambiguouslyfor me - the problem is in STM32F1.
I've also tried LisaM with only a led test programm on it - same result. Ublox5 GPS receiver has noticeable worse receive nearby the board.

I found yet one forum topic about it

The solution could probably be to switch off the HSI after HSE and PLL init. As I see, the HSI is switched on in rcc_clock_setup_in_hse_12mhz_out_72mhz function and stays on from that point.
By adding rcc_osc_off(HSI) at the end of this function could probably help.


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