88-108 MHZ BAND-REJECT FILTER (BUILT & TESTED ENCASED IN A DIE-CAST ALU BOX)

WITHSTANDS 80 W CW AT 1...70 MHZ and 136-175 MHZ and 50 W AT 430 MHZ

ELIMINATE "GHOST" SIGNALS ON 28 MHZ (!) OR ON 145 MHZ (!)  BY SIMPLY ADDING THIS FILTER BETWEEN YOUR ANTENNA AND TRANCEIVER.

Local 88-108 MHZ broadcasters can be so strong that may overdrive your SDR receiver, especially if you use an LNA. This causes the noise floor to increase over a very wide frequency range way outside of the 88-108 MHZ band and produce signals you can see them existing but in reality they don't! Nobody is really there! They are products of the strong broadcast transmissions. These products are so strong, they can sometimes mask weak wanted signals too!

​Christophe, F1JKY, president of the Amateur Radio Association of Dauphine's in France, did it again, he designed and prototyped a nice band-reject filter to greatly attenuate those emissions and thus "clean-up" the receiver from below 25 MHZ up to 1.5 GHZ.

The filter design, an optimized Chebyschev 7-th order band-stop, is excellent, the PCB and the high Q components are of high quality and the reception below and above the 88-108 MHZ broadcast band are not affected. The Return Loss is high from 10 MHZ to 1.5 GHZ except in the stop-band. Only there are a few dBs of loss close to the edges but reducing the center of the broadcast band so much, rewards you with a clean reception almost elsewhere in the spectrum. The -3 dB attenuation frequencies are on 80.4 MHZ and on 128 MHZ, while the loss is 21 dB  on 88 MHZ , in  the center of the band more than 80 dB and on 108 MHZ it is 17 dB.

His original realization is described here:  http://f1jky.fr/bidouilles/lna_pga103_schubert/lna_pga103_schubert.htm
and this webpage includes measurements. 
The Amateur Radio Association of Dauphine's website address is http://f1jky.fr

This high-power version of the filter has variable elements so the user can optimize the notch at the frequency of interest.