Hf Contest Front-End Cw Filter

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.

73’s Gabriel


2 thoughts on “Hf Contest Front-End Cw Filter

  1. Long time reader, first time commenter — so, thought
    I’d drop a comment.. — and at the same time ask for a favor.

    Your wordpress site is very simplistic – hope you don’t mind me asking what theme you’re
    using? (and don’t mind if I steal it? :P)

    I just launched my small businesses site –also built in wordpress like
    yours– but the theme slows (!) the site down quite a bit.

    Keep up the good work– and take care of yourself during the coronavirus scare!


    1. Hi,
      the theme used is “Justread” whithin worpdress repo.
      Also keep in mind that I own the server my website is hosted on so keep this in mind.
      So entire CPU; I/O; Quality RAM is serving my only.
      You too mate , take care during corona issue and hoping not to crash global markets.

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