Re: How do you like your pre-selector? #fdm-duo #pre-selector

Clint Chron

Hi Paul White,


I suspect that there would not be enough demand for the special filters to warrant Elad’s financial investment in the project.   The current Elad ham band filters, while effective, do not use a standard design.  Please keep in mind that the available Elad filters are wider than a ham band, so they are usable for some SWL bands.  I am hoping that Elad will provide schematics for the SWL/Ham bands using their FPCB-B3 and FPCB-H5 bare circuit boards. 


Here is what I measured on the Elad filters for the low/high -3 db filter points:


80M       3.2 – 4.5 MHz

40M       6.4 – 8.6 MHz                     standard 3 pole filter designed with Elsie would have a band pass of 6.6 – 8.3 MHz

20M       12.4 – 15.3 MHz


The current Elad circuit boards are very small and can probably only accommodate a filter with a small number of poles (max of 3 toroid coils).  A bare board could be redesigned to use filters that could be modeled with a program such as Elsie.  The board could be designed to use through-hole parts (no SMT parts) so that it would be easy to assemble.   If you only need a filter for a specific SWL band, then one could easily be built and installed in a small enclosure.  I have a AM broadcast band reject notch filter that covers 500 to 1600 Khz.  I use this filter to get rid of the ADC overload on my Duo (there are strong AM broadcast stations near my QTH).  With this filter, I can listen to the 200 to 500 Khz band.  With the typical AM band high pass filter, any frequency below 1600 Khz would be filtered out.


Here is a link to a HF band pass filter board that has continuous coverage of all bands (ham and SW) from about 1.7 to 64 MHz in 10 separate bands:


The board uses BCD control for changing bands.  I have designed a small BCD controller circuit board that interfaces to the DB9 connector on the S2 and Duo radios.  You could also use the Elad SFE Experimenter board to do the same thing.


Good luck.








From: [] On Behalf Of Paul White
Sent: Thursday, March 19, 2020 3:08 AM
Subject: Re: [EladSDR] How do you like your pre-selector? #fdm-duo #pre-selector


Hi, Clint
Isn't it a little disappointing that the available filters are designed for the amateur bands only?
I wouldn't have the skills to build on the unpopulated boards.

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