AM broadcast band filter

For the receiver I build a broadcast band filter. This should front end overload and intermod created by these stations and allow for better Ham band receiption. I also wanted to learn how to build my own coils.

I found a design at the vk3il blog. This filter was modeled with the ELSIE (free version). It is a 7-pole Chebychev filter with cutoff frequencies of 1.7MHz.


I started by winding some coils from 22, 26 and 30 awg magnet wire. I use a MingHe model LC100-A meter to masure these coils. I found holding the coils with my fingers didn’t make a sizeable different in the coil. What did make a difference was how tight the coile was wound and the lingth of the wire used. The size of the winding did make some difference but not as much as the amount of wire and how stable the winds where.

To make my coils I used a thick wall plastic tube. I put a hole with a T pin in the tube and put the 22awg wire through the hole. The wound the wire around the tube. Testing told me less then 20 turns would produce a coil with less then 2uh.

As I wound the wire I would use the LC meter to learn the value. When the value reached the 1.6 or 1.4uh needed I would put another hole in the tube and push the other end of the wire through it. I then secured the coil in place with some heat scrink.

Here are some pictures of the process and the results on the radio.

Coil tube. Whole made with T pin

Coil Measure.

AM broadcast bandfilter

Band before filter

Band with filter

I used 470pf instead of the 560pf caps. The result is a higher cut off frequency. It is 2.9MHz not 1.7MHz. I’ll correct this when I get the correct caps.


Start here:

I have a new radio. I picked up a KiwiSDR ( receiver from Seeed. (

The KiwiSDR was developed by the Funkamateur John Seamons ZL / KF6VO, is a branch of the OpenWebSDR project and realy started life as a kickstarter project.

This is the best HF (10kz-30mz) receiver I own. With the propagation so bad (its 2017) hams are using web based SDR receivers to make contacts. I share my SDR because I use other’s SDRs. Check out the list at (

There a a couple of web based SDR servers out. The first I found was This is a sound card based SDR. Meaning, It receives left and right chanles as the quaditure IQ data from the sound card. This limits the band width the software can receive. To receive RF, most people use a down converter like the SoftRock ( tuned to the band they want to receive and feed the output the the sound card. With multipule receivers and sound cards WdbSDR can supply multipule bands to the web. Also you could downconvert any band.

I have two softrock receivers and the software for the WebSDR and I’m working on them. The KiwiSDR is up and running now. Why? Because it came out of the box working. It’s 100% plug and play.

I think I like the KiwiSDR more than the Websdr because it is fully open source. Both the hardware ( and software ( are avaible. So you could build your own or modify it for your needs. The web interface is written in Python. All you realy need to do is plug it in (power, antenna, network) and connect to it with a browser (Not IE). It boots into you’re wired network via DHCP.

I’ll be looping the my house to make a wire loop antenna for it. For now is has a 100 foot long wire attached.

Technical data:

  • Frequency range: 10KHz - 30MHz
  • Operating modes: AM, AMn, LSB, USB, CW, CWn, NBFM
  • Bandwidth filter: Adjustable between 50Hz - 10KHz
  • 30MHz low pass filter
  • 14bit ADC with 65MHz clock frequency
  • SMA RF antenna connection
  • 3.3V SMA connector for GPS active antenna

There are several places to purchase the KiwiSDR if you are intersted.

You can purchase a KiwiSDR here. SeeedStudio


I’ve added a new SDR. The FlyDog SDR is use the KiwiSDR software with new hardware arunning on a RasberryPi 3.

Tradition is… Amature Radio Operators don’t get along with each other’s projects. Witness APRS.

As the KiwiSDR source code is open source and itself boarrowed from OpenWebRX, it could be considered fair game to fork.The KiwiSDR developers don’t quite see it that way. John Seamons (ZL/KF6VO), the leader of the KiwiSDR project has announced that despite the clones KiwiSDR development will remain 100% open source with any future updates also being available to the cloners should they choose to implement them. He also mentioned to us that the clones will also be able to contribute to the TDoA service and can be listed on the KiwiSDR ( directory. However, the reverse proxy feature will be limited only for official products. (Research needed here.)