Passband filters HA8LFK

Dear All,
is it possible to add the BPF of HA8LFK?

Did you already try to add these BPFs?

Looking forward,
Giulio IZ3EAW


  • by adding a BPF, you'd make it a single user receiver, unless everyone wanted to be on the same band! What problem are you trying to solve?
  • jksjks
    edited December 2018
    I hope Martin will often an opinion. He'll be the expert on this.

    That schematic resolution is terrible, but I think the switching diodes are 1SV271s:
    The $64 question of course is what the IMD performance of the switching diodes are and if they meet your requirements.

    Sending control voltage to them is another headache. The antenna switch extension has a "backend" for driving Beagle GPIOs (
    Here's a thread where Martin attaches to the Beagle P8 GPIO pins by soldering to the top of the Kiwi board:

    Be aware that the Beagle (and Kiwi) I/O is strictly 3.3V only and is not 5V compatible. If you backfeed 5V to either input you will burn them out. In the case of this particular diode switching arrangement the only question is if 3.3V is enough to drive the diodes into a properly biased condition (IMD again). You might want to use a 1-transistor, 1-resistor level shifter to get to 5V and offer some protection to the GPIOs.

    Fewer than 10% of the Kiwis sold are publicly accessible, so single-band filtering may make sense for a fair number of people and situations. But otherwise Jim is absolutely correct.
  • Hi Giulio,

    Happy Christmas.

    The switched band pass filter seems to be very similar to that found in many 1970 onwards Superhet design based Amateur radio transceivers, so I would expect that (as John has already stated) if you drive the switching diodes correctly, it would probably be adequate for the purpose.

    However that may not be the best solution for use with the KiWi SDR.

    I think we need to better understand the problem you are trying to solve before anybody makes any proper recommendations.

    Can you provide a bit more background information ?


    Martin - G8JNJ
  • Dear All,
    thank you for the feedback. Close to my QTH (300m), there is a contester. During the weekends he usually goes with 1K so: OVERFOW on the whole spectrum. I thought I could mitigate the problem using BPF but given that I want to maintain my RX free for everybody, this choice is sensless.
    Giulio - IZ3EAW
  • Hi Giulio,

    That is a problem for you.

    I don't think the simple band pass filters would help in that situation as they probably wouldn't provide enough stop band attenuation. You would need to use filters with a much better defined cut-off of the type used by amateurs when operating in contests from the same site. Bandpass Filters.pdf

    Which bands does the amateur use ?


    Martin - G8JNJ
  • Dear Martin,
    All I will find a friend that can host my Kiwi + LZ1AQ loops.
    Congrats for your antennas!
    Giulio IZ3EAW
Sign In or Register to comment.