Contest Club
QRV since 1993.

Bandpass filters for PI4CC

Contesting is all about the ability to listen. Undesired strong signals, even out-of-band, can cause undesired QRM due to overloading receivers. Harmonics that end up in the next higher bands are even worse. With our current coax stub filters we can suppress small frequency-slices (notches), but the majority of the spectrum passes unattenuated. So, we embarked on a project to remove all signals that are outside the bands of interest.

This bandpass filter project aims at serveral goals:

  • Ability to handle high power (1 kW)
  • Low insertion loss to avoid heat build-up in order to avoid a cooling fan.
  • Adjacent band attenuation > 80 dB.
  • Easy reproduction, modular setup.
  • Rugged, stable housing.

The project is finished and the project details has moved here.
Construction details, needed parts , tips and layout are here.

A view of the 6 filters installed at our patch panel. From top to the bottom: Stackmatch/power splitter, hp-filter + W3NQN filter, coax/rotor patch panel.
On the right side our (remote) rotor control cabinet.

Each plot can be blow-up with a click.

10 meter top view.

10 meter bandpass.

10 meter S11.


15 meter top view.

15 meter bandpass.

15 meter S11.


20 meter top view.

20 meter bandpass.

20 meter S11.


40 meter top view.

40 meter bandpass.

40 meter S11.


80 meter top view.

80 meter bandpass.

80 meter S11.


160 meter top view.

160 meter bandpass.

160 meter S11.


It not easy job to to build a good filter. You will need some skills, tools and patience to fulfilll the job!

Needed tools are at least a VNA to trim the coils. Prefferd a spectrum analyser to check the performance.
A work branche to modify the enclosure, to drill the holes and do some metal works.

To get an idea about the cost for a 10 - 80M filter :

  • The C's per filter vary between 45 and 81 euro.
  • An enclose 26 euro.
  • A set of PCB's 25 euro.
  • 2 female N connectors 10 euro.
  • Some copper tube.
So the cost will be between 115 and 145 euro per filter.

If you still want to continue to build your own filter(s), you may look here.

If you decide to buy a set of PCB's, you will get a nice tool to tunee the needed coils for free.

Attenuation per filter in other band(s).

Last update 18-6-2017


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