137kHz 5 pole elliptical low pass filter.

Bare bones Low Pass Filter - interior view.

Another seriously good high power low pass filter - for 136kHz.

Having built several amplifiers for the 2200m band, the occassion has risen again, to build a suitable high power filter, that will remove the harmonics to the required acceptable levels, when transmitting at significantly higher power levels.

To be really successful, one needs to look at removing or reducing greatly, the second and third harmonics of the output frequency from the RF output of the RF amplifier. The method chosen here was to use a 5 pole elliptical low pass filter than gives the required attenuation at the frequencies of concern and does this surprisingly well.

The program I used to design, optimise and plot the filter, is called ELSIE and is available from Tonne Software. The link is provided below. The site has a student version (free) which has limited number of elements that can be used in the design. This version is what I used and is more than adequate to perform all the tasks required.

I can highly recommend using this software tool in helping with your filter designs.

Again, I was pleasantly suprised when the design results closely matched the final tested filter results. Again, a good result. The component values were not exactly as designed but were suitably matched to be close. Within a few per cent. Let the results speak for themselves. Another job done.


2200m LPF Schematic

 Initial schematic of design used in  ELSIE.

2200m LPF Plot

 Theoretical response plots using  ELSIE.

2200m LPF Response

 Actual LPF measured  response.

Useful Links


VK5FQ website
12/02/14 Start build of new website.


Steph - VK5FQ
Adelaide, South Australia,