FS: Kiwi Switcher PCB

edited April 24 in General Chat

Hi All,

Sorry if I'm not allowed to post adverts but I have an item for sale that maybe of general interest. After spending a lot of money and time, I don't want to throw this away. It's a 'glue' PCB with:

6-20V to 5V buck power module @2A

Active antenna input

2x other antenna inputs

Compatible with kiwiSDR antenna switch extension (now built into main software project)

Notch filters - see trimmer caps in picture - for reducing loud BC stations

1.5MHz high pass on 3 channels

2m to 24MHz converter, easily configured to make the kiwiSDR show the correct frequency (e.g. 145.500MHz)

Will accept Si5431/SI570 to adapt to a 70cm converter (never used this)

Why am I selling? I made a new board with a better 2m converter and put down an SMD position to remove that 100k mod resistor you see on the back. The 120MHz oscillator needs replacing as I pinched it for the new board. Oscillators are £11 in Mouser.

100x55mm size

A neat solution for anyone that wants to have several antennas on their kiwiSDR!

Photos below hosted on my own server to save bandwidth. Will negotiate over price.

73, Rob.



  • Hi Rob,

    That's actually really interesting.

    I have a proposal document for a Kiwi "accessory box" containing most of these functions plus more. It's geared towards supporting 4 Kiwis. For example the HF front end (with antenna switch, notching, filtering, balanced antenna input etc.) has 4 outputs. As does the GPSDO or GPS splitter (option).

    It's also meant to contain a wide input voltage power supply module using quiet boost/buck conversion and post linear regulation to finally solve the Kiwi power problem in a more reasonable way.

    But detailed design has not been completed.

  • Hi John,

    This is an 'accessory box' but we all have our own definition of what it has to do!

    The problem is everyone will want some thing different. I put in a 5V switcher having found the 7805 replacements to be the cheapest way. People are hyper-aware of any noise issues but I have not found any with a Murata module. It does have a common mode filter on there, plus a lot of 10/100nF ceramics

    Switching multiple receivers is not catered for but it would be possible to gear these together somehow. I found the logic outputs of the Beagle board are not quite 0V when off, that plays havoc with FET gates, so included a resistor network to sort out the levels.

    The 2m converter is a problem here, with a local 1kW pager on 152MHz. I changed the board to put on larger coils and other ways to help the Q and filtering.

    As you contributed a chunk of your life to this project, I can send you a blank PCB for free? Also KiCAD files are available for all this.


  • Hi Rob,

    Just some thoughts,

    In order to extend the KiWi to cover additional bands, I was musing over an idea to implement a configurable external down convertor.

    The main issue seems to be switching RF filters to avoid aliasing from the mixing products.

    How about using a synthesised LO and mixer on the input to shift the signals to a fixed frequency 30MHz bandwidth IF, at UHF or higher. Then mix it back down to 0-30MHz using a second synthesised LO and mixer.

    By using different input LO frequencies, you could choose which 30MHz wide chunk of the spectrum is down-converted, and you could make the frequency range selectable without having to switch RF filters.

    Having some form of external band pass filtering at the input would be useful, but this could be provided externally as part of the antenna system, and as it would not need to have a precise passband, something like an antenna diplexer may be enough to provide the required characteristic.



  • jksjks
    edited April 25

    Glenn has already designed and tested a 0-2 GHz Kiwi "frequency extender". I haven't had time to look at it much yet. http://sonic.net/%7En6gn/OSHW/KiwiExtender.html

  • Ah, that's probably where my thoughts originated.

    I must have seen it, but didn't remember the detail.

    Job done :-)



  • Hi All,

    Glenn's converter is a lot more complicated and ambitious than I had in mind, being a simple ham radio man on 2m/70cm. After all there are lots of SDRs out there with wideband coverage, it seems like covering the same ground differently.

    I do have the option of using a small micro to set the frequency of a Skyworks PLL. They have been busy releasing low-jitter parts recently. Using the Beagle logic outputs and antenna selector to set the L.O. is feasible. But the problem of filtering remains.

    Locally here the pagers render Beofang's finest useless. Getting rejection of 152MHz takes fixed filters hand tweaked. Or a helical notch at that frequency.

    73s, Rob

  • jksjks
    edited April 25

    Hi Rob,

    Okay, understood. Sort of like how any LF/MW/HF Kiwi frontend module for the accessory box absolutely has to contain set of dedicated, tunable series traps for the AM BCB. Since so many people live in a town with a local blowtorch not too far away (causing ADC overload problems).

    I would very much like to see your KiCAD. I think the design of the proposed accessory box will definitely be more of a community effort since all of you have the expertise in these areas I do not. KiwiSDR will simply be an aggregator of the ideas and put them into a manufactured product.

    But it's still very early and I've put little time into it with everything else that's been going on. However these problems deserved to be solved in a more consistent way. And in a way that is compatible with the existing Kiwi-1/Kiwi-2 products rather than being part of some future product alone.

    One of accessory box ideas is to make it hold a number of "modules", say 4. One would be the standard HF frontend. One for power supply. The other two could be for optional modules (e.g. GPS splitter/DO) or even a custom user-built board.

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