I have added this simple preselector to my RX. (from LF today - RSGB publications)

Advantages : parts are easy to find  - it is easy to build - verry efficient to pick up little signal in a verry small bandpass.

Inconvenients :if you want monitoring a large bandpass with your SDR, the signals outside de BP of the filter are excluded : the best way is then to include a bypass position (use then a 6 position rotary swich), first bypass the whole preselector, pick the wanted signal , and then tune it using the other postions of the rotary switch.


Table of positions of the rotary switch :

pos 1 10kHz-40 kHz
pos 2 21kHz-90kHz
pos 3 45kHz-200 kHz
pos 4 100kHz-400kHz
pos 5(*) 210kHz-600kHz


(*) use only 1 X 500 uF section for the 210-600 Khz position


The RF parts are to find at Mouser.com - see table below for the references.

100mH 710-744747 1107
47mH 710-744747 1473
10mH 710-744721 1103
2.2mH 710-744721 1222
1mH 710-744721 1102