Power Supply Noise
Posted: Fri May 04, 2018 4:01 pm
Hi,
Just for curiosity, I decided to look at the power supplies with scope. My Portsdown is fed from a 18V battery from which is derived the various voltages to power it. The RPi is fed from an Ebay type regulator set to 5.1V. 3 78XX chips feed the other units with 12, 8 and 5 volts respectively.First I measured the 5.1V supple close to the RPi. It was showing around 100mV of a spiky signal which, my scope said, was at 200KHz or so.Next I look at the 8V (modulator) supply. Here is a more sinusoidal display, also about 100mV. Now for the shock. The input (18V) supply was showing 400mV of spiky noise. This puzzled me as , normally, regulators reduce noise considerably, especially when decoupled correctly.
I should add that the RPi was not in transmit mode when these measurements were made.I should also add that it all works perfectly so am I worrying over nothing?
Comments appreciated, thanks, Gordon
Just for curiosity, I decided to look at the power supplies with scope. My Portsdown is fed from a 18V battery from which is derived the various voltages to power it. The RPi is fed from an Ebay type regulator set to 5.1V. 3 78XX chips feed the other units with 12, 8 and 5 volts respectively.First I measured the 5.1V supple close to the RPi. It was showing around 100mV of a spiky signal which, my scope said, was at 200KHz or so.Next I look at the 8V (modulator) supply. Here is a more sinusoidal display, also about 100mV. Now for the shock. The input (18V) supply was showing 400mV of spiky noise. This puzzled me as , normally, regulators reduce noise considerably, especially when decoupled correctly.
I should add that the RPi was not in transmit mode when these measurements were made.I should also add that it all works perfectly so am I worrying over nothing?
Comments appreciated, thanks, Gordon