Chers all !
How many of us dreamed about having some kinda extreme narrow preselector for CW contests when lower bands is full of bigguns and transceiver front-end is getting overloaded?
Well, I did it ! for 40 meter band and only some cw channels,otherwise it would be extremely expensive to be honest.
Basically it is just a crystal 3 poles ladder filter, channel selection relays, T/R relays, an Arduino controller and few t37-6 toroids for L-match circuitry for each channel.
Because the original design using a simple switch to change channel relays and wanted an Arduino afterwards, I needed an extra transistors board for Arduino interfacing.Also, a special care was to design T/R logic to avoid damaging X-tals if PTT cable is disconnected and transmitting 100 W straight into filter.To compensate this, I found that Icom has a T/R pin on DIN connector (apart of SEND RCA) ,pin that presents 6V dc when RX and zero when TX.
So was as simple as pie to use 6 V into NPN transistor base to create a TCVR detector.If cable not connected then filter goes into ByPass mode to send all the power to antenna.In the next future will implement Icom Ci-V protocol to change TCVR freq using filter rotary encoder when filter is enabled.
The video bellow is self explanatory, I let Icom to SSB filter while enabling / disabling my new gadget to observe real bandwidth.