When powering the FPV video transmitter (VTX) and camera with main battery, noise from ESC and motors might cause jumping lines and interference to your footage. In this post we will discuss how we can filter out noise in our power.
ESC’s and motors draw large amount of current, and the fluctuation of motor speed and current draw introduce noise in your power system.
Solutions to Noisy Power Source
The simplest solution is to use a separate battery only for your FPV equipment, however the downside being the extra weight. Alternatively you can use a power filter (as known as a LC filter) to clean up the “dirty” power. I wrote a post on how I built one before, check my LC filter build log out.
Here is the schematics I follow to build my own LC power filter.
For the inductor, make sure it can support the current in the application. Exceeding the rated current would cuase the inductance to drop due to saturation. Lower inductance will affect the filtering effectiveness.
For the capacitor, make sure it’s rated above the voltage of the application. 25V is a good value for 3S and 4S LiPo batteries.
For RC hobby purposes, I don’t think the value of capacitors and inductor matter too much. I have seen people reported good results with 100uH to 500uH inductors, 0.1uF ceramic capacitor (For high frequency noises), and 100uF to 1000uF capacitor with Low ESR. (Important: low ESR caps are extremely important to ensure good filtering)
Why can’t I see this noise from my multimeter?
Noise that affects your FPV gear is normally high frequency voltage spikes DC multimeters are unable to detect them. To Observe them requires much more sophisticated test equipment such as an oscilloscope.
But how is this connected on the quad Oscar? Do you connect it between the battery and the battery terminals on the ESC, like you do for a low esr cap? Or do you connect it between the battery terminals and your VTX? Power the camera from the VTX after first filtering the power entering the VTX? Ive read both articles…pretty sure you never say how to actually hook this up – sorry.
What I don’t get in all of this is why filtering isn’t part of the VTX / Camera?
At a per unit cost of less than a dollar each IMO this would be a trivial thing to add which would greatly enhance the overall performance of a FPV product.
We begin to see better power filtering now in VTX such as the Tramp and Unify Pro HV.
I guess it all comes down to design and cost, extra filtering makes VTX bigger/heavier and more expensive to make.
Thank you for the info. Is there any way to calculate the required capacitor value as a decoupling capacitor in a circuit (eg. a motor driver circuit) that a motor is connected also. Thanks in advance.
The diode is not only for polarity protection. It filters one “half” of the ripple away. You can simulate the behaviour i.e. with LTSpice.
Couldn’t you run the FPV off the balancing plug but off all the cells in parallel? Wouldn’t this eliminate the video noise?
you can do that, but the noise is still there, because the power source from balance plug is exactly same as the discharge plug
Could you show how this is wired up, along with the mini voltage regulator on a mini quad?
just goes pcb to filter to vtx