Monday, March 5, 2012

Great little low pass filter board

I had decided to build an all-band low-pass filter to use with my propeller projects and others.  In adding up the costs and spending a little time looking around, I decided to purchase a great little kit from Virgil Stamps K5OOR down in Texas rather than roll my own.  His low pass filter kit fit the bill exactly.

I am working on interfacing it to the propeller and plan to do band switching automatically based on the frequency chosen.  This board will easily handle up to 100 watts of power.  You can see plots of the filter response here.


  1. Howdy;
    I too built that board by K5OOR expecting it
    to handle 100 watts OK. I was going to use it with
    my CCI EB-63 (140w from 2 X MRF$%$) throttled back too 100 watts. Virgil,K5OOR even assured me it would
    handle the 140 watts from EB63.
    The kit was an easy build, but boy, those torif inductors are are SMALL and close together.
    To make a long story short, the LPF Network got
    very, VERY hot when handling just 50 watts CW for a short time. I am talking about blistering my finger if I touched the windings on a toroid!
    I was running into a 300w dummy load.
    Then I checked the Input SWR's on all bands.
    They were all OK except 80m, which was 3:1 on 80m.
    I double checked all solder joints, windings, and cap values. I do not have an L/C Meter to check the
    actual inductance values on the toroids. I just went by the instructions.
    So I emailedVirgil and asked him how I should
    proceed to troubleshoot this problem, ALL I ot was
    a snotty "THAT IS IMPOSSIBLE!!". I had already checked ALL parts placement,even removing several caps to check the values. (They are packed SO close and tight, you can't read the values on the "inner" onces.

    Any advice on how to proceed to fix this is appreciated. I would LOVE to use it even at a lower wattage IF I can fix the 80m problem. Does YOUR K5OOR 100w LPF heat up so much when you use it?h yeah, I did NOT key down for long periods, which would overheat anything....just a few seconds at a time to plot a graph.
    THanks and 73, Ken AD6KA

    1. Hi Ken,

      I was just rereading some comments on my blog posts and ran across your comments about the K5OOR filter board and wanted to get back to you (albeit a bit late) about how you made out on that project? If you are still having problems, maybe we can take it offline by email at and see if we can work it out. Otherwise, let me know how you got on with the project and if I can help in any way, happy to do so.

      73's de Jeff KO7M

  2. Thank you for providing us with such precise information. Continue to make similar posts. I needed a low pass filter only a few months ago. I came upon the Anatech Electronics website while searching on the internet. Then I have decided to place my first order with them and I received all of my low pass filters on time and at a better price than I had expected. If you require a low pass filter, place your order with them and save money.