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  1. #1

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    Kraft Spectrum info

    I am looking for a pin out on the module in a Kraft Spectrum 6 radio. I have one on 53.2 that I am interested in converting to 2.4 since I can't find what I did with the receivers on 53.2 AM. I think it would be great to fly this old transmitter on 2.4.

    Thanks,
    Pete

  2. #2

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    RE: Kraft Spectrum info

    As Phil Kraft died not too long ago, you need to travel over to SAM Talk at Yahoo, as someone there knew of what you are speaking. Takes forever to get ahold of the operators there too.

    Wm.
    Thousands of Laser Cut parts, thousands
    And plans too

  3. #3

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    RE: Kraft Spectrum info

    Try Radio South

    L.
    Cherokee Flyer
    Club SAITO #696

  4. #4

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    RE: Kraft Spectrum info

    if the module in the spectrum is am then any am narrow band rx will work if fm then you can use jr or airtronics.I think I have a narrowband am on 52 something if interested let me know

  5. #5

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    RE: Kraft Spectrum info

    Right now it is on 53.2 mHz AM. On 53 mHz there is no narrow band. The channels are spaced at 100kHz apart. I want to convert this to 2.4gHz. I was looking for info on the pin out for the internal module. I can find the modulation line with a scope if I can't get the info. I know some of the pins that go to the module control the voltage meter on the front of the transmitter. I would like to keep the meter functional even though I will remove the module and replace it with one of the hack modules avalable.

    I love the feel of this transmitter and would like to give it a new life.

    Thanks,
    Pete

  6. #6

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    RE: Kraft Spectrum info

    The Kraft Spectrum was the best natural balanced transmitter ever made in my opinion.
    You can hold that thing with just two fingers per hand and it would just sit there perfectly
    level. I like the feel of this transmitter also. It’s also one of the hardest transmitters to
    find modules for. Good luck on your conversion, maybe I'll give it a try once you are done.
    Let me/us know how it turns out.

    Ron

  7. #7

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    RE: Kraft Spectrum info

    I have all the modifications done to the Kraft Spectrum 6. It has the FRsky DIY module in it. Other than a short antenna and a bind button it looks about the same. There were some modifications I had to do to get it to work with this module. I would be glad to share this information if anyone is interested.

    The Kraft Spectrum 6 now works great on 2.4 gHz.

    Pete

  8. #8

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    RE: Kraft Spectrum info

    I for one would like to know your process and what mods you had to make
    to get this transmitter to work with the FRsky DIY module. Would you have
    any photos?

    Ron

  9. #9

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    RE: Kraft Spectrum info

    I can open up the transmitter and take some pics later (I'm at work now). I will try to write this up as follows:

    You will need to open up the back of the transmitter. Pull out the module. You will see two rows of female pins in the transmitter that the module plugged into. Ignore the top small row. On the bottom row as you are looking at the back of the transmitter the right pin will be the + power. The center pin will be the modulation PPM line. The left pin will be the ground. I got a pin connector that would plug into the female connector in the Kraft transmitter to wire everything to.

    On the FRsky (or Corona) hack module there will be 3 wires. + power, ground, and the PPM modulation input. DO NOT CONNECT THE PPM MODULATION INPUT TO THE CENTER PIN ABOVE FOR THE MODULATION OUTPUT OF THE TRANSMITTER!!!!

    The PPM modulation output of a Kraft is inverted with respect to all the other popular transmitters on the market. Also the voltage swing on the Kraft is larger than the FRsky (or Corona) module wants to see. So the modification I needed to make is to invert the modulation PPM pulses and lower the voltage. I did this with a simple NPN transistor inverter and I used a 5 volt regulator on the collector. (If you need I can detail this.) So I built a little PCB with one transistor, a regulator, and a few resistors. This PCB must be connected to the power pins (per above) in the transmitter and the PPM modulation pin. The output of this PCB goes to the FRsky PPM modulation input line. The FRsky also gets it's power from the pins in the transmitter. (I have thought about a different way to do this would be to use a single op-amp as a inverter with negative gain. Any thoughts out there on this?)

    The little PCB that inverts the signal I built up as small as I could. Seeing I was using parts that I had on hand, I used a larger regulator than I needed but it works. I enclosed the PCB with some heat shrink tubing with 4 wires coming out of it, +,-, PPM modulation input and PPM modulation (inverted) output. I put this little PCB under the PCB that the original Kraft module plugs into with double stick tape. I put the FRsky module with double sticky tape where the original Kraft module would be located. Once everything is wired and mounted there is one last step, mounting the bind pushbutton and LED PCB. FRsky unlike Corona does not give you a drilling template. I very carefully measured the centers between the LED and bind button to be .312 inch. I located this on the top of the transmitter between the antenna and the slider for channel 5. I drilled the two holes with a .130 inch drill on the top. Next I used two 2-56 screws and nuts to mount this assembly inside the transmitter.

    Antenna....remove the Kraft assembly. The hole in the transmitter is too large for the FRsky antenna mount. Inside the transmitter I used a quarter inch washer and on the outside I used another quarter inch washer. The washer I used on the outside is thin copper and matches the gold look of the transmitter very nice. I got them at Lowes for pocket change. I put the original antenna ground lug into this assembly then fed through it the FRsky RF connector to be used as the antenna mount.

    The original Kraft antenna wire (white) with a solder lug is still in the transmitter. I put a piece of heat shrink over the solder lug to insulate it and tucked it under the module mount PCB.

    One of my goals in planning this out was to be able to put the transmitter back to 53.2 mHz if I wanted. The only thing I can not undo was drilling the holes for the bind button and LED. I don't think I will ever restore the transmitter back now. I am going to leave it on 2.4 gHz. I do have one more of these Kraft Spectrum 6 transmitters to think about doing a modification to.

    I hope this helps. Let me know if you need more information. This can be done in a weekend once you have all the parts for a low cost. I hope I didn't get too detailed but I don't know your background so more info is better than not enough. I've also done a Kraft series 74 for a good friend and it involved similar work.

    There is a thread in RCG that is over 100 pages long on the FRsky hack DIY module. Lots of good info there.

    Happy Holidays,
    Pete

  10. #10
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    RE: Kraft Spectrum info

    And when you are done it looks like this.
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    Club Saito # 677-Team Boca Bearings-Star Collectibles Muscatine-Glowhead Brotherhood #19

  11. #11

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    RE: Kraft Spectrum info

    Pete,

    Congrats on the conversion. Have you flown it yet? Everything you've done
    sound pretty easy but I may need a schematic showing resistor values, their
    location in the circuit, and the location of the four wires. I should be able to
    work it from there. I was surprised at the price of the 2.4 module you used.
    Looks like a cheap way to go to 2.4 ghz and bring life back to one of your
    old loved transmitters.

    Ron

  12. #12

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    RE: Kraft Spectrum info

    Ron

    I have not flown the system yet but I have done range checks that are great. The last range check I put the receiver on a block of wood in the bed of my truck and it worked great. I would have thought that the bed of the truck would have blocked a lot of the signal but it was not problem.

    I will send you a PM about me getting you some drawings to do the modifications I have done.

    Pete


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