Not that I have very much QRM problems here, but I live in an urban area so there is always some of it. Sometimes there is a level of S7-S9.
Fortunately, it is not always that loud and it is not always present. Despite many searches in neighborhood, I have not yet succeeded in locating it.
So I was looking for a way to suppress this QRM. Now there are many so-called "Noise Canceler" on the marked, commercial and homebrew.
Since this is for me an experiment I did not want to spend too much money on it. Finally, I'm not sure if it will work so it had to be "Home Made".
On the DARC website I came across a diagram of DK9NL - Hanns.
The principle is based the fact that the interfering signal coming from the main antenna is the local interfering signal superimposed by an auxiliary antenna phase that are canceled interference.
It seemed to me a fairly simple circuit that was easy to build myself. To make it easy DH4YM - Dirk has a PCB-service where you can order the board. He provides a nice, completely drilled board for a fair amateur price. There are no special or SMD components used. Most could be found in the junkbox and otherwise at your local shop and of course, on the Internet.