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RF Sampler

Discussion in 'Home Brew' started by Moleculo, Jan 21, 2009.

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  1. Moleculo

    Moleculo Administrator
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    Here's a homebrew RF sampler that's easy to build. I use this to connect to an Oscilloscope and Frequency counter (T off the BNC plug) It's pretty straight forward to build and the pictures pretty much explain themselves.

    [​IMG]

    Here's the inside...note the resistor and the ferrite core.

    [​IMG]


     
    #1 Moleculo, Jan 21, 2009
    Robb and rabbiporkchop like this.

  2. Sonwatcher

    Sonwatcher Active Member

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    2k resistor ?
     
    #2 Sonwatcher, Jan 21, 2009
    Last edited: Jan 21, 2009
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    You missed it by a power of ten and then some. It's a 100 ohm resistor. Brown-black-brown.
     
    #3 Captain Kilowatt, Jan 22, 2009
    Beetle and tecnicoloco like this.
  4. Sonwatcher

    Sonwatcher Active Member

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    Ok, read the bands as red . Thanks !
     
    #4 Sonwatcher, Jan 22, 2009
  5. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Here's another good one to use Every toolbox needs one of these

    and another that is in the ARRL Handbook is quite handy as well. It is made from copper pie and a copper Tee and end cap. I can't find a pix online anywhere but I will try and find my old one I have here somewhere. It is great for VHF and UHF pickup but will work on HF as well.The great thing is that it does not upset the SWR on V/Uhf.
     
    #5 Captain Kilowatt, Jan 22, 2009
  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    That's OK. I said it was a 200 ohm resistior when in fact it is a 100 ohm unit. :headbang Corrected above. :D
     
    #6 Captain Kilowatt, Jan 22, 2009
  7. Cityboy

    Cityboy Active Member

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    I also did this RF sampler and works great with my B+K 35mhz osc. I also did one more thing to make it convient to hook my frequency counter on and sample at the same time. I drilled another hole in the box and put another bnc connector with another 100ohm resistor that connects on to the same point as the one for the scope. I then drilled a hole in the side of my Wawassee jb-1004 freq counter and put a bnc connector in the case and grounded it and ran a wire from the center terminal of the bnc and connected onto the wire that samples frequency that went around the bridge wire between the coaxial input of the freq counter. So now I don't have to have 2 coax jumper cables; 1 going from the transmitter to the freq counter and the other to the dummy load. It only requires 1 bnc jumper cable to the one I put on the side of the counter and it does a great job. I checked against my other jb-1002 fcm Wawasee and it is dead on in its sampling.
     
    #7 Cityboy, Mar 8, 2009
  8. galyndavis

    galyndavis Supporting Member

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    great idea!

    I bought the set of these off ebay, one for after the radio and another after the amp . I paid ( i was ashamed when i took the covers off) around 200 dollars for the set. Thanks for the post ....it will save others from paying too much for something this easy to build. Post like yours help folks to achieve their goals without going bankrupt doing it. There was a time when radio guys made all their tools.....very cool.


    thanks for sharing,

    galyn davis
     
    #8 galyndavis, Jul 9, 2009
  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    I have an MFJ-264 dummyload. I installed a small toroid over the wire going from the RF connector to the load resistor and wound it with a half dozen turns of wire. I connected this to a BNC jack that I mounted in the lower right corner of the case. This allows me to make measurements without having to insert anything inline as the dummy load is connected to an MFJ-1700B antenna/transmitter switch.
     
    #9 Captain Kilowatt, Jul 9, 2009
  10. GnG8d

    GnG8d Well-Known Member

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    If I understand, you used the wire wrapped around the toroid to the BNC jack? I have a couple of these dummy loads here and I like this idea over yet another device inline.
     
    #10 GnG8d, Jan 27, 2011
  11. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Correct, the wires from the toroid simply connect to the BNC jack.
     
    #11 Captain Kilowatt, Jan 27, 2011
  12. GnG8d

    GnG8d Well-Known Member

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    One more question. You placed the toroid between the connector and the resistor. The pic in the OP shows a resistor between the toroid and BNC. Whats the significance of that?
     
    #12 GnG8d, Jan 27, 2011
  13. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    The resistors just drop the voltage into the scope or freq. counter etc. I didn't use any resistors as I usually use a 10:1 probe on my 'scope and terminate the input to the counter with a 50 ohm load if necessary. If you use a 1:1 probe or run high power then go ahead and install the resistor.The value is not critical at all. I just have 100 watts so I didn't bother.
     
    #13 Captain Kilowatt, Jan 27, 2011
  14. GnG8d

    GnG8d Well-Known Member

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    Thanks CK. I'll have to tear it apart further. It has a 3/8"x0.06" metal strap connecting the SO259 to the resistor, not a wire, but it could be made into a wire.
     
    #14 GnG8d, Jan 27, 2011
  15. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    It doesn't matter what the connection is between the jack and the resistor as long as the toroid will fit over it. i did mine years ago and don't remember if I left it as a strap or changed over to a more flexible wire but either way it will work.
     
    #15 Captain Kilowatt, Jan 27, 2011
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