When i use the CHIPs on board battery connector to charge a LiPo battery, my SNR drops below 2.5, but when i disconnect the LiPo battery from the CHIP, my SNR goes up to 5 - 6.
Is this an RF noise problem or something else?
Probably load sharing issue. Are you able to measure power at the input of the CHIP?
You can set some register values on the AXP209 to divert less power to charging the battery: AXP209 - linux-sunxi.org
I made the mistake of assuming that the USB micro port would handle the power needs of the Outernet RX and charge the battery. I never expected the battery to be charged at any more than 500ma, but I can see now that the total amps is too much. The CHIP has a charge input connection and NTC recommends that you use this option for running the CHIP with high USB loads and charging. So that is what i will do. Thanks for your help, very much appreciated.
Can you please confirm that when using the Charge-In port of CHIP do you still see the SNR drop when battery is used or this phenomena is disappears?
I can not say yes, the problem is fixed by using the charge input on the CHIP, but I can say that it just added another layer of problems.
I had problems with the LiPo not getting charged, no matter what power input i used. I had problems with the CHIP turning off as soon as the Rx gets power and sometimes the CHIP would not turn on or off.
I noticed that the Rx/LNA sometimes had power even when the CHIP was turned off.
So is all this just a sign of a faulty CHIP board or some issue with noise from the power supply?
What i can say is that i have removed the LiPo and i am not using the charge input.
I will try a 12v - 5v dc to dc switch mode power supply and a 12v battery + solar panel and see if that affects the SNR and CHIP in odd ways.
I need to look into all this some more and get back to you.
This morning i tried the on board battery and micro USB combination and had no problems with SNR.
So 5Ah LiPo and a mains phone charger powering the CHIP via the micro USB is working, no SNR problems.
Using the charge in option makes no difference to the SNR.
So it does look like it was a load sharing issue as @cyoung said.
It looks like the charging current for the LiPo and the outernet Rx was pulling the voltage down to a point that odd things were happening with the SNR and the CHIP.
I measured the volts and amps from an after market mains phone charger today and got without a battery connected 4.71v 900ma for a short time at startup then it settles down to 670ma at around 5.02v.
With the battery connected, i measured 4.63v 1.2A at startup and then settles down to 4.69v at 1A
So on the day of the bad SNR, the voltages must have been too low for the whole setup.