(3 customer reviews)



  • Designed to help HF radios and receivers that struggle with front-end overload from AM broadcast interference, such as Xiegu radios X6100, X5105, G90, G106 and SDR receivers.
  • Lightweight and portable design, only 3 inches (77mm) in length and weighing just 20 grams. Perfect for Parks on the Air (POTA), Summits on the Air (SOTA) and Field Day.
  • Tested up to 20 watts with SSB, CW and digital FT8.
  • Quick and easy to build, see online instructions here.
  • High quality C0G (NP0) capacitors and Micrometals toroids.
SKU: N/A Category:

Kits and Prebuilt filters also available on Amazon with free prime shipping here.

All kits and prebuilt filters sold on this website, Ebay and Amazon are Version 2 now. Version 2 has much higher AM band rejection. If you specifically want version 1 please contact me.

The K9DP QRP broadcast interference (BCI) filter kit allows QRP (low-power) amateur radio operators to reduce or eliminate unwanted broadcast interference in their signals. Primary designed to help HF radios and receivers that struggle with front-end overload from AM broadcast stations, such as Xiegu X6100, X5105, G90, G106 and SDR receivers.

This lightweight and portable kit is ideal for use in field operations such as Parks on the Air (POTA), Summits on the Air (SOTA), and Field Day. It has been tested at power levels up to 20 watts with SSB, CW, and digital modes, and its small size and low weight make it easy to take with you wherever you go. Measuring only 3 inches (77mm) in length and weighing just 20 grams, it's a convenient choice for on-the-go operations.

The kit includes all of the materials and components needed to build the filter, including BNC connectors, capacitors, enameled wire, toroids, and a printed circuit board. The high quality online instructions provided with the kit will guide you through the process of soldering the components onto the board and assembling the filter, step by step. Once the filter is built and tested, it can be easily attached inline with your radio equipment using the female BNC connectors.

Overall, this kit is a great way for radio operators to enhance their radio’s performance and improve their communication experience. These filters have a 50Ω impedance and are symmetrical, so it's not important which end is the input or output.

Caution: High SWR can damage the filter. The filter should be inserted inline between the transceiver and tuner, rather than between the tuner and antenna. If your radio has an internal tuner, be sure to use a resonant antenna or an antenna with a matching circuit, such as an EFHW (end fed half wave), in combination with the filter.

Click Here For Build Instructions

Video by Steve KM9G testing version 2 of the filter.

Video by Thomas K4SWL testing the filter in the field.

Video by W6IWN

Additional information

Kit or Prebuilt

Kit, Prebuilt, Board Only


Female BNCs, Male/Female BNCs

3 reviews for K9DP QRP BCI Filter

  1. Ken W.

    I received the kit today and assembled it.
    At first I was a bit intimidated by the small parts, I assumed it’d be a bit bigger, but the assembly went with no problems.

    I ran some tests to see how much it blocked the local AM stations.
    First thing I did was tune the radio to one of the most powerful local AM station and then put the filter inline with the coax feed line. The signal from the AM station was dramatically lowered, I could hardly hear it. So this filter really works!!

    I then changed bands to 80, 40 and 20 where I’d been having the biggest problem and the noise level was way down and the AM station overlay was gone.

    I then switched to the 10 meter band where I have to use the antenna tuner built into the G90 to test what kind of heat might build up in the capacitors. I started off transmitting low power (1 watt) FT8 and saw no temperature increase. I then bumped the transmit power to 5 watts and let the radio transmit a number of CQ requests (10) and again saw no temperature increase. I kept following this pattern and bumping the transmit power in 5 watt increments until I reached max output. Each time I used a Raytek MiniTemp laser thermometer to measure the temperatures of the capacitors. The ambient room temp is ~67*, the capacitors never exceeded 72* during this experiment. I realize this isn’t conclusive and really didn’t push the unit very hard but it is a positive result.

    Overall I’m, very satisfied with the purchase.
    Good job!!

  2. Steve

    Just a note to thank you for designing/building/selling the filter for the x6100.
    Across the valley from me are transmission towers from commercial stations in Cleveland Ohio. Needless to say 10 and 15 meters bands were overpowered.

    The filter has cleared all that up for me. In fact, on 10 meters today I contacted W1AW volunteer station in Hawaii. 4600 miles on 10 watts with full copy both ways.

    Thanks for giving me my 10 and 15 meters bands back!

  3. Larry Goodwin KC6WOG

    I’ve got an AM station just a half-dozen miles away from me and it’s signal tends to swamp the front end of some of my QRP rigs, depending on my operating location. A quick search brought K9DP’s page to my attention, so I ordered a kit. You can hardly beat the price and convenience, getting everything you need for $20, shipped. It took about half an hour to assemble and I was ready to go. It’s already proven to be a BIG help, entirely eliminating BCI interference. A welcome addition to my go bag!

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