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://www.arrad38.fr/bidouilles/Notch_FM/Notch_FM.htm and this webpage includes measurements. The Amateur Radio Association of Dauphine's website address is http://www.arrad38.fr
ORDERS for a complete PCB Module EUR 11.28 The prices do not include 24% Greek VAT applicable only to individual buyers from European Union.
The PCB Module includes a high-quality ENIG 0.8mm thick with 1 oz gold over nickel over copper FR4 PCB (20 x 37 mm) that comes with all SMD components factory pre-soldered. RF capacitors and high Q inductors are used in the filter elements. Two SMA female connectors are also supplied unsoldered. A short 1 mm trim is needed on the central pins for not exceeding the pcb pads as you can check before soldering. If you want one of the two connectors to be male, please leave a note when ordering. Or, if you need them soldered on the PCB again, please leave a note. The shipping is with registered mail (your signature is required upon delivery).
We usually ship the next day and it takes about a week to 10 days for USA or Australia, less than a week for Europe.
If you want to order from France, check with Christophe , F1JKY as he can offer better price on shipping: Web Site of ARRAD ( Association of the Radio - Amateurs Relays of the Dauphine ) : http://www.arrad38.fr
88-110 MHZ Band-Reject Filter
Eliminate "ghost" signals on 28 MHZ (!) or on 145 MHZ (!) by simply adding this filter between your antenna and receiver.