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Cheap and simple DIY LC filter for FPV

Simplicity at its finest – LC filter

Lc filter closeup

If you are running your FPV gear on the same lipo that is powering your motors there is a high chance that you have problems with noise lines and interference in your fpv video.
This is very common and you probably recognize it from this image:
noise in fpv video
The reason for this is because of noise that your brushless motors and ESCs output when they are under load as you increase the throttle. As your motors rev up or down to balance your multicopter they are make the current fluctuate. The varying current makes your lipo voltage to go up and down resulting in noise in your FPV video.

Luckily there is a simple fix to this problem! The name of the solution is a LC filter. A LC filter is basically an inductor/coil “L” and a capacitor “C” working together. The inductor smoothens out the current flowing through it and the capacitor smoothens out the voltage. There is not much more to it besides the plugs – it’s almost like magic.

Items needed to build the LC filter:

The ferrite ring is the same as what is used on most ESC rc wires. When choosing a capacitor make sure it’s rated for more voltage than you are planning on using. It’s such a cheap component. Regarding the uF rating there seems to be little to no evidence of how it affects the performance of the filter, I used one rated 1000uF.

This is how I built mine:

Step 1 – Gather all parts and prepare you soldering iron.

components

I really like working with silicon wires. They are flexible, easy to strip and solder. You can use this tool for stripping them.

Step 2 – Coil the positive wire around the ferrite ring.

Coiled wire

You should wrap it tight together without overlapping them. This is what I’ve been told and how I’m doing it. Some people overlap the wire without any signal problems.

Step 3 – Solder JST plug and the ferrite ring

coil soldered to capacitor

In this step you can decide how long you want the JST wires to be. As long as you keep them within a reasonable length it doesn’t matter much. Be sure to solder the positive wires to the + pin of the capacitor. The negative (-) pin is often marked on the side. The order of coil and capacitor of the LC filter should be: lipo -> coil -> capacitor -> fpv gear.

Step 4 – Solder the negative wires

LC filter soldered

This is the last step unless you want to cover it with tape or shrink tube. You should not leave the capacitor pins exposed as it could be short-circuted by metal or carbon fibre. I covered them with two dabs of melt glue.

Step 5 – Check polarity!

You should ALWAYS check polarity of a component that you’ve soldered before plugging it into your application. Use a multimeter like this one to make sure that there is no short circuit or reversed polarity.

If everything seems alright it’s ready to be plugged in and tested. Enjoy a much clearer video feed!