What is a KX3 Band Decoder

Are you a KX3 owner?  Ever wished you could squeeze band info out of your KX3 like you can on the K3?  Control big amplifiers, automatic antenna tuners, band switches?

Well you can!  I designed a KX3 Band decoder package.  It sniffs your KX3 serial PC connection for band information and generates the band signals found on the 15 pin K3 ACC connector.  It uses the same band signal drivers and coding as the K3 and shows up on the same exact pins!  This allows you  to connect any of your ham equipment that you can use with a K3  band selection data to the KX3!

Owners manual here and Theory of Operations here

The KX3 band decoder fits inside of a 3″ by 6″ by 1″ box.  It has two PC (3mm stereo) connectors so you can plug into your KX3 and your PC (you don’t need the PC if you have KX3 in AI (auto info) mode).  There is a 15 pin compact female sub D connector, just like on the back of the K3.  You can power this device with anything from 8 volts to 19 volts (safe for same battery/power use as the KX3)

The KX3 band decoder uses a tiny postage stamp size Arduino and the same exact driver chips as is used inside the K3.

No configuration required.  Plug it all in and instant band decoder.

I originally built this up on a wire bread board and used it on my Marshal Islands trip to drive my automatic band pass filter.  When I got home I decided I wanted to have a more robust version so I did a ‘board’ layout and improved the power supply circuit.  My miniumum board order had to be 10 boards.  I’ve built most of them up.  I don’t drill out the tiny front panel as I do not have equipment for the D sub so if you want one you will need to do the front panel yourself.

A few have been sold but I still have a number available for sale to those interested. Pricing is $75 which inludes US postage to US locations.  Orders placed between 8/4/2015 and 10/5/2015 will be shipped on 10/6/2015.

20160701Sold out!  Now taking a list.  Next buy will be in the fall. I need at least 9 on the list to do the group purchase.  If you are interested please send your info via this post and I will put you on the list.



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40 Responses to What is a KX3 Band Decoder

  1. Don Solberg (K9AQ) says:

    I have a KX3 that I am trying to interface to a homebrew solid state linear for auto band changing. I have written my own band decoder using an Arduino and it works, sort of. It works good if it is the only device on the serial line. However I also need to run Win4K3Suite and Log4OM logging software. My decoder can not handle the increased traffic on the serial line so I am looking at alternatives.

    Have you used your band decoder along with other applications talking to the KX3 serial port?


    • admin says:

      My kx3 band decoder does not actively communicate with the Kx3. My kx3 bd only listens to the kx3. Basically it acts like a serial port sniffer and does not interfere with any kx3 to other device (like a pc) communications. My kx3 bd has 2 1/8 inch jacks that just pass through the tx/rx lines. Kx3 bd simply listens to the line from the kx3 and picks out band info.So, yes, I use my pc with my kx3 nd!

  2. Dan Codianni says:

    Interested in buying kx3 band decoder.


  3. Interested in buying Kx3 band decoder says:

    Thanks, just now getting into Arduino applications and would like to use this with my KX3, KAT500, and Win4KX3 Suite software. Sounds like a fun project to learn from.

    good on QRZ.com

  4. Bob says:

    does this decoder also pull out XV band information?

    I am looking to pull out a line I can set to high or low for each band, including the multiple XV (transverter) band as well.

    eg: i want to know when the band is say 70cm, so I can then use this to automatically switch the 10M RF output to the XV and not the antenna – does this provide the required functionality – if so, certainly interested!

    • admin says:

      Bob, the decoder simply creates the 4 bcd signals found on the 15 pin din located at the back of a K3. No other signals are generated. I’m not a vhf’er so I cannot comment on whether the bcd signals are sufficient for what you would like to do.

  5. Jeff (K8KZB) says:

    I would like to buy one please let me know by my email when you will have more ready 🙂

  6. David G3WGN says:

    I’d like to be ‘on the leest’ for the next buy.
    If you prefer, I can have it shipped to a US address.
    73, David

  7. Jeff says:

    Awesome that you are ordering!!!! I hope to use mine for field day with my Bandpass filter 🙂 Let me know when you need my money.

  8. Howard "Pat" Patterson says:

    Planning to use my KX3 as IF in my VHF/UHF Rover. Using KX3 Utility Command tests it looks like the VHF/UHF RF frequency is returned in the “IF” command response. I configured the KX3 with a transverter XV2 with RF of 222, IF of 28 and no Offset. With radio tuned to the XV2 defined band 222.000.000 is displayed on VFO A. Sending IF command to radio return “IF00222000000” plus the RIT offset and mode. Looks like if the contents of you “band definitions” were changed to reflect VHF bands rather than the standard 160M-6M ranges the outputs would work to drive antenna switches and PTT keying for the correct VHF/UHF band selected.

    Please add me to the “list” for 1 Band Decoder.
    Pat, W5VY

  9. Howard "Pat" Patterson says:

    After further thought, I think I’ll try driving some relays with an Arduino Mega I have. I failed to look closely at the 15pin D connector on your board. I would rather have an output for each VHF/UHF band rather than the “K3” Band 0-4 scheme. Your scheme really is sweet to mimick the K3 function but I don’t have a K3…or widgets that are built to connect to the K3 15pin D-Sub!
    Enjoyed looking through you Blog. First licensed in 1964. Worked in Engineering and IT.

    Thanks es 73,
    Pat, W5VY

  10. Bill, W4ISH says:

    Love the ability to auto switch the bands on both the KAT500 and the KPA500 when used with the KX3! But I do have a slight problem: I have the BD in line between the PX3 and the KX3-to-KXPA100 Adapter (yes, I drive the KPA500 with about 23 watts from the KXPA100!) . The only problem is, the KX3, when setting the PA MODE to “ON”, resets it to “OFF” after about 5 seconds. This normally will happen when the KX3 does not sense the RS232 cable making the complete circuit from KX3 –> PX3 –>BD –> Adapter –> KXPA100. But with the BD inserted in the line, the KX3 thinks the RS232 line is not connected, and therefore switches the PA MODE to OFF.
    When I move the BD to between the KX3 and the PX3, then the PA MODE will stay on, but the AMP and Tuner usually will not switch bands until about 30 seconds or, if I turn the Tuning knob, it will switch in about 10 seconds. I have the KPA500 RADIO setting on K3 (or it wouldn’t work at all!) but the slowness of switching seems to be an eternity when I’m in the heat of operating.
    Is there a way to speed up this switching, or is this a function of the KPA500 and/or KAT500?

    • admin says:

      Hi Pat. That is very odd. If you review the pdf on the KX3 Band Decoder you will see that the BD does not interact with the serial port. It simply ‘sniffs’ the serial data. The serial line phone plugs are a straight pass through. The ‘sniff’ is done through a 220 ohm resistor that drives the base of a transistor which has an overshoot diode to protect the transistor.

      If you look at the schematic in the pdf you will see the 220 ohm resistor. You could increase the size of that transistor. 1K would probably still work, maybe even 4.7K. Although, that 220 ohm should not cause a degradation in the serial signal.

      GL, Paula NX1P

    • admin says:

      Bill, final thought your second configuration. Do you have AI (auto information) set to on? It sounds like the KX3 is not automatically sending band information.

      73, Paula NX1P

  11. Jim Noe says:

    Please add me to the “decoder list.”
    Jim K6AR

  12. Cool Arduino application; I’m interested pending details.

    Two things to consider: First, it would probably work with the KX2 as well as the KX3. I don’t think you would have to do anything except test it. Second, many users of the encoded band data from K3 ACC use it to drive a band decoder (e.g. Top Ten Band Aide) that outputs individual band lines for antenna switches, bandpass filters and the like. (Many such devices don’t digest the encoded data directly.) Does your Arduino have enough output lines to do that? It might need a buffer amp or two between the chip and the outputs but it could save users an extra box.

    • admin says:

      Two additional lines are exposed on the 15 pin connector and 2 lines are exposed internally to a header. None are programmed into the arduino so you would need to down load the sketch, get it running and add code for the additional lines.
      Paula NX1P

  13. Guy Hamblen says:

    Paula, please put me on your list for your KX3 Band Decoder when you run another batch. Thanks, Guy/n7un

  14. WT2P says:

    Please add me to the list for the next group purchase, de WT2P

  15. Tony says:

    Does this covers VHF and UHF BANDS TOO

    • admin says:

      6 meters is covered. I don’t have the 2 meter option in my KX3 or K3 so I don’t know what the band info is. I could add that band info and set to what ever the K3 outputs.

  16. Gary Slagel says:

    I learned about your BD via the expert amp email list. I’m not sure from your website, does the BD come assembled or as a kit? Also, I’m using the kx3 with the kxpa100 so currently my ACC1 is attached to the kxpa100. Would I put the BD in series by plugging the kx3 ACC1 to the BD KX3/PC port and then the other BD KX3/PC port into the kxpa100? Or split the line from the ACC1 between the BD and the kxpa100? If one of these scenarios will work I want to be on your buy list! Thanks. KT0A

    • admin says:

      Hi Gary,
      BD come assembled or as a kit? It comes assembled.
      Would I put the BD in series by plugging the kx3 ACC1 to the BD KX3/PC port and then the other BD KX3/PC port into the kxpa100? Or split the line from the ACC1 between the BD and the kxpa100? If one of these scenarios will work PUT IN SERIES. Send me your call so I can put you on the list.

  17. Gary Slagel says:

    Hi Paula,
    I’m interested in ur BP… wonder if its a kit or a built up product? Can you put me on the list for the next group buy? Thanks – Gary/KT0A

  18. Daniel Codianni says:

    Are you still selling decoder? thanks dc


  19. Dr Bruce Macaulay says:

    Good morning.
    I’m interested in purchasing the band decoder.
    Please put me ‘on the list’
    Bruce G4ABX

  20. Santiago Sanyé González says:

    I have a KX3 #5595

    I’m interested about information of this band decoder for this model.

    How much it cost?
    How to order ?
    What is delivery time?

    Thanks in advanced

    Santi Sanyé

    • admin says:

      Hi Santi, I am building a list for my next run. The price is $75 plus overseas shipping. It looks like I may do a run early in 2017. I will keep the list updated.
      Tnx 73, Paula NX1P

  21. Santiago Sanyé González says:

    Thanks Paula

    Can you put me in the next list for one band decoder ?

    Tnx in advanced

    EA3KX/QRP Santi Sanyé

  22. Kevin Magde says:

    Greetings Paula,

    Put me on the list for your next batch of KX3 band decoders.

    Kevin AC2KL

  23. John Klewer says:

    I am interested!

  24. Please include me on the list for your next buy.

    Richard, KC8RP

  25. al5m says:

    Hi Paula,
    I am interested in purchasing your KX3 band decoder. Please add me to your list.


  26. Jean-Louis DOMANGE says:

    Hi Paula.
    Interested in purchasing your KX3 band decoder.
    Questions :
    Do you supply the 15 pin cable with it ?
    What is the shipping cost to France ?


  27. K1VG says:

    I would also be interested in purchasing a KX3 band decoder out of the next batch.


  28. Daniel says:

    i am interested too in purchasing the KX3 Band Decoder.
    Give me a reply if possible.


    Daniel DL3DW

  29. Tatsuro Fuse says:

    Are you still selling decoder?
    de ja1pwk

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