Announcement

Collapse
No announcement yet.

DD coil nulling... again.

Collapse
X
Collapse
 
  • Page of 1
  • Filter
  • Time
  • Show
Clear All
new posts
Previous template Next
  • #1

    DD coil nulling... again.

    I know there was a lot discussion about that. In short, I don't have an oscilloscope, so I'm trying to null the coil as per one of the guides found on forum (measuring voltage in Rx loop). I have Tx connected to pcb (shielding is not connected anywhere- should be?), multimeter set at 200mV and connected to Rx. Now, moving slightly two loops, I should get as less mV in Rx as possible if I understood the procedure. The problem is that my cheap multimeter doesn't show any voltage, doesn't matter how I move the loops. Does it matter how Tx is connected to pcb because I'm not sure now if I did it correctly (I mean start of the loop and end)? Any thoughts? Cheers

    Greg
    Tags: None
  • #2
    Check TX side first. If there is no signal you cannot sense something on RX side too.

    Comment

    • #3
      I knew it's going to happen! With still no success of getting any voltage in Rx loop, I connected it to pcb. I soldered wires on the front side of the pcb, where all the components are. I played with loops a bit to get as best depth as I can. Machine was working ok, but depth was poor. So, I thought, time to buy oscilloscope and decided to put my Troy X3 all back together. After plugging original coil, when I start it, it makes one longer beep (normally is one short) and there is no reaction to metal. I checked all the wires coming from pcb to the plug and looks like all wires are ok. I'm 90% sure I have not done accidental shorts on the pcb and 99% sure no mechanical damage to any of the components. Any ideas? Thanks

      Greg

      Comment

      • #4
        I take it you are on A.C.

        My meter does not do a very good job of measuring the peak to peak on my TX. With a scope it's 16V with my meter it measures 6V not tried the RX but guess it's not going to show much.

        Comment

        • #5
          Probably you can build a bridge rectifier with four 1n4148 diodes to convert AC signal to DC voltage and connect it between your RX coil and multimeter in lower DC mode.
          also you can try to use same bridge and connect it between output of RX preamplifier and your multimeter.
          Also you can try PC oscilloscope that not required any hardware and works with your computer sound card. Like Visual Analyser http://www.sillanumsoft.org/prod01.htm or any other.
          Or search Google for "sound card oscilloscope" you will see many solutions.
          Or buy on eBay PC oscilloscope like Hantek 6022BE or some regular oscilloscope under $100.

          Comment

          • #6
            Originally posted by Waikiki_Sweep View Post
            Probably you can build a bridge rectifier with four 1n4148 diodes to convert AC signal to DC voltage and connect it between your RX coil and multimeter in lower DC mode.
            This idea will not work due the forward-voltage drop across the diodes.

            Comment

            • #7
              You could use an opamp precision rectifier these can often see down to 10mV or so. S

              Comment

              • #8
                How about to connect TX to oscillator and RX to computer microphone input (or high gain audio amplifier) using capacitor?
                1,2,3 kilo Hertz will be audible (not sure for 6 or more).
                Then slowly move coils to catch low sound point.

                Comment

                Previous template Next
                Working...
                X