LC Filter and FPV

LC filter is one of the most basic filters in electroincs, which comprises of just one inductor and one capacitor in its simplest form. This circuit is widely used by FPV hobbyists to suppress noise in power created by ESC and motors.

What is an LC Filter?

An LC filter is made up of an inductor (L) and a capacitor (C). It’s that simple.

An inductor resists changes to the current flowing through it, while a capacitor resists changes to the voltage across it. See this post for a more sophisticated version of power filter.

It’s essentially a low pass filter, allowing lower frequencies to go through while attenuating higher frequencies.

Buy LC Filters

Looking to buy some LC filters? Here are some options I found that are suitable for RC.

Make sure the LC filters you are getting meet the voltage and current rating for your application.

How LC Filter Improves FPV Experience

In the quadcopter, Motors and ESC’s can generate noise which can affect your FPV video quality.

During flight, motor speed is constantly changing in order to stay airborne. The change of motor speed means change of current drawn by the motors, and voltage ripples (fluctuations in voltage level), which is basically noise.

The most common signs of noise are disturbing lines appearing across the screen when we are flying.

An LC filter can suppress the noise in the power getting to your FPV setup (e.g. your VTX and FPV camera). You might or might not need an LC filter. Some voltage regulators have some degree of power filtering ability,  but an LC filter can enhance filtering.

IMAG1241

IMAG1242

LC Filter vs. Low ESR Capacitor

I often get asked which method should be used to combat noise in their mini quad, LC filter, or Low ESR capacitor. But I must say they serve very different purposes and applications.

LC filter is mainly used to stop noise getting to their FPV system, it does not reduce the amount of noise in the original power. On the other hand, by putting low ESR capacitors in your power, you should notice a reduction in the noise level.

Make sure to check out my tutorial about what low ESR capacitors are and how to use them in a mini quad.

LC filter has current rating due to the inductor’s current limit, and therefore it’s mainly used in low current circuits. You often see LC filters built into the 5V and 12V circuits on flight controllers or PDB for powering your FPV setup. And they are usually more effective than only using capacitor alone.

On the other hand, when using only low ESR capacitors, you only need to make sure the voltage rating is high enough.

Building an LC Filter

The value of capacitor and inductor changes the resonant frequency. This makes it possible to suppress noise more effectively if you know the noise frequency. However you will still get certain extent of filtering effect using random capacitor and inductors, so do not worry :)

If you know how to work out the exact capacitance and inductance you need for your application, good for you! But if you don’t it’s okay, we are not building a rocket and it’s going to work just fine :)

Here is how you connect the capacitor and inductor.

lc-filter-circuit

When choosing capacitor, ensure the voltage rating meets your requirement. or example if you are connecting the LC filter directly to your LiPo battery it should support your LiPo battery’s voltage. As for capacitance, the larger the better, I think 100uF to 2000uF is a good range.

You can buy inductors, or you can make one yourself with a Ferrite ring (toroid) and some wires. Choose the length and diameter of the wires carefully. Ideally you should be able to wrap around the ferrite ring at least half a dozen times. And the wire gauge should be large enough to support the current.

If you are making your own inductor, I find it work better with just the positive wire wound on the toroid. When winding the cable around the ferrite ring, DO NOT finish your winding back to the starting side, it should exit at the opposite side.

As for the capacitor, any electrolytic ones should do just fine. They are widely available from old radios or PC parts for example. Or just pick some up from eBay, they are very cheap. It’s best to use low ESR capacitors which are much better for noise filtering purposes.

Make sure to place the capacitor on the output, where it connects to the VTX and camera.

Conclusion

LC filters are great because they are so simple and cheap to make or buy. They can help attenuate or even eliminate “noise” completely if you are having “lines issues in your FPV feed”. If using only capacitors doesn’t seem to solve the issue, you might want to consider adding an LC filter for your FPV system :)

Edit History

  • Feb 2014 – Article created
  • Jun 2018 – Article Updated with LC filter options

33 thoughts on “LC Filter and FPV

  1. alto

    It would be nice to include examples of before/after LC filter or mention how bad solder connections can be a major culprit.

    Reply
  2. Mathijs Groothuis

    Will a decent filter filter out _any_ distortion or just reduce the distortion? I use a low ESC 16 volt capacitor as distortion (nothing else yet) based on this video: youtube.com/watch?v=ZhvuQJPGHzU

    But when I give throttle peaks my OSD overlay goes away for a nano second and then goed back again, for every throttle spike. So no OSD reboots, but I do some flicker which is clearly correlated with the amount of throttle.

    Is this normal or can I do something to reduce this even more?

    Reply
    1. Oscar Post author

      Sounds like you need a proper LC filter for your FPV setup. make sure your OSD, camera and vTX have common ground too.

      Reply
    2. Chabrollson

      Hi guys.
      I agree with Oscar.
      Usually when osd flicker, you need to fix all the vtx and camera to the same ground on your fc.
      The lc filter really help to get a really good quality but if your ground are separated it’s not work better.

      Reply
  3. Cereal_killer

    Hi Oscar, I just swapped out some Afros for little bee’s and the video interferrance is HORRIBLE now! I had been using a small lc I built as described here (DIY ferrite ring w/ cap). I actually had a bad one of those same blue 1×2″ buck regulators you show above (the big black FET on it blew but the output cap & 330uH L were good so I physically cut the board and used it as an LC filter). This works pretty well and really makes a large difference but I’m still getting some annoying lines in the video (I can live with them but I’ve already spent time on it so why not make it perfect [if possible] ya know)

    I’m running my vtx off direct 4S battery voltage, do you think my next step should be a different value inductor or cap (right now it’s a 330uH / 220F) or to run the vtx off UBCC at 12v?

    Reply
    1. Oscar Post author

      Yea the littlebee ESC have very good active braking and it causes some serious power noise.
      you will need something better for filtering. consider buying a proper PDB with voltage regulator and filtering, like the DemonRC Core

      Reply
    1. hansi

      when one solders capacitors one is increasing the resistance of the path between the solderpoint and the capacitor it self with such a long connection as you have used for illustration above. I would like to give you a tip without coming off a knowitall, please dont take this the wrong way?

      If you solder the leads much tighter to the capacitors base you will get MUCH better flow of electrons as of opposites in the above picture. Capacitors are best off resting on a flat insulated surface with their “legs” going through the surface and beeing soldered from the backside. This way you will increase the flow and reduce heat and wasted energy.

      Thank for the huge contribution you have given to the quad community and all the hours you spent online assisting others for free. I hope what litte insight i bring into the quad scene will not go unnoticed for it is a thing of importance indeed.

      hansi

      Reply
  4. CB1

    Seems that way.
    They are both Foxeer HS1177 cams from Surveilzone. I may play with them more to see if I can get them any better.
    I have a RMRC-PICO-WIDE-V2 cam on my Hellbender122 that is excellent as far as being focused. Just seems odd to me that I can’t get the HS1177 cams any clearer. I would say that they both are the same as far as clarity.
    Thanks for the reply!

    Reply
    1. Oscar Post author

      Try the Runcam Swift, i found it to give me better performance (if you haven’t seen my test/review yet)

      Reply
  5. CB1

    Hello Oscar,

    I have two racing quads, both are on 4S running HS1177 camera, Aomway 200mw VTXs and directly connected to my PDB (shared power with the ESCs). I am not experiencing any noise in my video feed, however the video image just doesn’t seem sharp enough (a little blurry). I have focused both cameras as good as I can using a focus image and through my HD TV as well as adjusted the internal camera settings from some videos that I have seen on YouTube that offer some suggested settings for the HS1177. But the image is still a little blurry, in my opinion.
    Would a LC filter like this help my issue or should I look at something else to resolve this? http://www.ebay.com/itm/FPV-LC-Power-Filter-2A-LC-FILTER-for-RC-FPV-Aerial-Photography-US-STOCK-Y0M6-/282018491043?hash=item41a99caaa3:g:zgIAAOSwZ1lWgKVK
    Thanks for any advise!

    Reply
    1. Oscar Post author

      from what you described, i don’t think it’s your power, it sounds more like your cameras.
      LC filter won’t sharpen your image unfortunately, if you are not getting any noise then LC filter won’t do anything for you.

      Reply
    2. Chabrollson

      Take care, lot of camera pretend use hs1177 but if you get blur is usually because it’s a numerical camera and not a real cmos.
      For myself i use from lot of year only Sony super had cmos and it’s work really fine. The only matter with this one is you need to set up all day long when sun light turn..

      Reply
  6. Matt

    I think you will find the parts in a pc power supply. The motherboard doesn’t have the parts you are looking for :)

    Reply
    1. Nivaldo

      Hi Florian0311, I have the same doubt!? The filter is for the vTx or Cam? Today I tried the LC Filter just on the vTx and the lines don’t disappear.
      Tomorrow I’ll test it putting in the fpv cam!

      Reply
      1. t.goat

        If your vtx has 5v out, it’s better to put lcfilter before vtx, then power camera from vtx. That way it’s getting double filtered.

  7. Hannes

    Hi Oscar,

    I’m currently planning a built with littlebee ESCs which are quite notorious for voltage spikes that take out electronics like FC, VTX, or the camera. Would it be sufficient to solder a capacitor to the Vin and GND of the polulu step-down on the PDB or should I use a different combination of LC-Filter and BEC?

    Reply
  8. Romain

    Hi Oscar,
    I am suffering white stripes across my FPV video. I tried changing VTX, VTX antenna, camera, FPV goggles… nothing changed.
    So I tried to add a BEC 5V for the FPV camera power supply and the type of LC filter your describe here for the VTX power supply. Stripes are still there.
    https://youtu.be/ED97Aa0-SbY

    Any idea on what could be the cause and potential solutions ?

    Cheers

    Reply
    1. Oscar Post author

      do you get this before take off? if you don’t then it’s probably the power, if you always get this, it’s could you your signal.. check your VRX as well?

      Reply
      1. Romain

        Thanks for you reply. I do get this only after take off… But if this is due to power issue, the 5V BEC and LC filter should have fixed it, right ?

  9. Dmitri

    Hi Oscar,

    Thank you for your posts, they really help.

    I wanted to ask for your advice on filtering noise with 2-battery setup. I power FPV (vTx, camera and minimOSD V2 board) from a separate 3S, 12V battery # 2 (minimOSD is connected thru 12V-to-5V linear regulator.) From APM (powered by main 3S/12V battery # 1) I get telemetry data (Rx) and ground form battery # 1. I connected grounds of both batteries. Everything works except that I am still getting some horizontal lines on video. My question is if, by connecting grounds or two batteries, I am adding noise from battery # 1 and, if so, how I can reduce it in 2-battery setup by using LC filter or ferrite ring (and where to insert them to.)

    Thank you!
    Dmitri

    Reply
    1. Oscar Post author

      Using a separate battery for FPV gear you shouldn’t get any noise… there could be something else is wrong in your setup…

      Reply
  10. Levi

    Hi Oscar,
    I used a Schaffner Common Mode Choke(RN202-2-02) for an inducer, similar to a very popular FPV LC Common Mode filter Choke(RN202-1-02), yet I went with the model that can handle 2A, instead of 1. I set it all up, and when I connected I noticed that I had a video signal, but it was just black, with some static on a repeating, regular time interval. The difference between the two inducers is the mH and the mOhm, but I can’t figure out why my new inducer does not work. Any thoughts?

    Reply
  11. bncache

    Hi Oscar
    I just wanted to suggest smaller lighter coils to make the filter lighter.

    With leads like these:
    no.mouser.com/Passive-Components/Inductors/_/N-5gb4?P=1z0z819&Keyword=passive&FS=True
    and even smaller, leadless like these:
    no.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=47&storeId=10169&categoryId=700000005466&pageSize=25&beginIndex=1&showResults=true&pf=110137774,110178564
    Just make sure they are specced to handle the current drawn by the camera combo.

    bncache

    Reply
  12. Norbertas

    Here you can calculate what do you need for your LC filter:
    circuitcalculator.com/lcfilter.htm
    I’m filtering 1200-1500HZ freq. so for 1000uF (1000E-6H) capacitor i need to do only few turns on ferrite ring (~20uH or 20E-6H). When i do more turns on ferrite video gets very dark and loosing colors.

    Reply
  13. Gabor

    Nice post!
    I would like to do this in my FPV project. ~3.7 volt 1S lipo, the FPS setup works fine with it,but when I connect the quadcopter and give throttle,noise appears! how shall I start? what do I need for this config to make it work?

    Thank you!

    Reply
    1. Oscar Post author

      how much lift can you quadcopter carry? Get a 100uH – 200uH inductor, and a 50uF-100uF capacitor, solder them together shown in the pictures.

      Reply

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