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  • Very nice feature to consider.

    In the future our MDs will have "scanners" to look for clear frequencies and hop there automatically!
    Some quality Radio control kit for models does just this.

    Andy, there are some big beacons at 12k from russia, plus the SAq Tx for swedish subs on 17.2kHz (but only twice a year!)

    I guess you use Winrad, Rocky, digital crystal set, Saq Rx.??


    If you wind a big coil 1m dia 50turns thin wire and attach it to an audio cable LH input into soundcard - download Saq SD Rx you can see stations in the 1 to 22kHz band live, using your soundcard as a spectrum analyser.

    You could offer your IGSL up to this to get the actual transmit frequency too !!!!!!

    Steve

    Comment


    • Resistance & Impedance

      Originally posted by simonbaker View Post
      Looks very nice, similar to experiments habitbraker and I were playing with. http://www.geotech1.com/forums/showp...&postcount=356
      I wonder if it is a little difficult to get L2 and L3 with those low resistance values.
      Also the low inductance of L2 implies fewer coil turns, and since magnetic field is proportional to current * turns (I think??), are we really getting as much bigger field as we think even though the voltage/current is a lot higher? Probably something we need to calculate, the magnetic field for these high-voltage coils.
      Also watch out for phase shift across your "dropper" divider circuit. Not much, but little things can add up...
      I like it! Hope you build it and show us some experiments.
      -SB
      Hi Simon, in that previous post you appear to have forgotten that at DC you have a DC resistance. Any AC signal in a coil means that the coil does not have resistance, it has impedance. You mentioned a 400% difference if I remember correctly.....
      The impedance is also given in Ohms which causes some people to forget that these "Ohms" are slightly different!!
      The impedance varies with the frequency, a higher frequency gives a higher impedance with the same coil......
      Hoping that I have just "jogged" your memory a bit.......this is why changing frequency changes many other things as well as the null of a search coil head for example.

      Have fun.

      Have a great day.

      Regards
      Andy

      Comment


      • Null change over soil

        All, we generally null in a garage or whatever.

        When using these detectors over AVERAGE soil is the null level the same. ?

        OR

        should we null over AVERAGE soil. - As the fresh air case is of little consequence!


        S

        Comment


        • TX coil power considerations

          Short question about the oscillator power delivered to the TX coil. In the current TGSL is see about 30-40 milliWatts of power in simulations. What kind of power levels do we need to double the ground penetration depth?

          Comment


          • Originally posted by joop View Post
            Short question about the oscillator power delivered to the TX coil. In the current TGSL is see about 30-40 milliWatts of power in simulations. What kind of power levels do we need to double the ground penetration depth?
            To double the depth, you would need to increase the TX power by 64 times. But this brings with it a whole host of other problems.

            Comment


            • Originally posted by Qiaozhi View Post
              To double the depth, you would need to increase the TX power by 64 times. But this brings with it a whole host of other problems.
              Thanks! Judging from some of my simulations I can get a 10 percent depth increase by optimizing the TX oscillator in the TGSL. Not much, but worth trying.

              64 times the power gives about 2 Watts for the oscillator. So we need some kind of large, hip-mount battery pack (to heavy to mount on the detector stem). Also, we need to re-design the transmit coil. Not impossible, quite a challenge.

              Comment


              • Getting the power is no problem - Li Ion or Li po have plenty to spare.


                Keeping it out of the Rx front end is though. You cant null all of that away.

                So then you may req a higher dynamic range Rx.

                Plus if you throw masses of energy into the soil - you magnetise it and it blocks your 'Vision' for small things deeper in the soil - for want of a better description.


                A heap of trade offs concatenated.

                S

                Comment


                • Thanks for sharing Golfnut!

                  Maybe will give it a try anyway, would be an interesting experiment. Get myself a good coil and make the TX power adjustable, see what happens when you crank up the power.

                  Okay on the RX frontend. Will look into that...

                  Comment


                  • Originally posted by der_fisherman View Post
                    Hi Simon, in that previous post you appear to have forgotten that at DC you have a DC resistance. Any AC signal in a coil means that the coil does not have resistance, it has impedance. You mentioned a 400% difference if I remember correctly.....
                    The impedance is also given in Ohms which causes some people to forget that these "Ohms" are slightly different!!
                    The impedance varies with the frequency, a higher frequency gives a higher impedance with the same coil......
                    Hoping that I have just "jogged" your memory a bit.......this is why changing frequency changes many other things as well as the null of a search coil head for example.

                    Have fun.

                    Have a great day.

                    Regards
                    Andy
                    I see what you are saying, but there are ways to estimate both the resistance and impedance components of a coil at a given frequency (in other words, estimating the reactance X) by looking at the response. The AC resistance and the impedance should make up the reactance.

                    The AC resistance can be different from the DC resistance as people have discussed, partly due to radiation, partly due to skin effect (not much at VLF freq), and partly due to "proximity effect" (bundle of wires), the last being the one I'm curious about.

                    I'll try to get back to an experiment to see how much the AC resistance really differs from the DC resistance. It is mainly important to those who are interested in hi-Q TX oscillators.

                    I think that was what I was trying to get at.

                    -SB

                    Comment


                    • Inductive and capacitive loads

                      Originally posted by simonbaker View Post
                      I see what you are saying, but there are ways to estimate both the resistance and impedance components of a coil at a given frequency (in other words, estimating the reactance X) by looking at the response. The AC resistance and the impedance should make up the reactance.
                      The AC resistance can be different from the DC resistance as people have discussed, partly due to radiation, partly due to skin effect (not much at VLF freq), and partly due to "proximity effect" (bundle of wires), the last being the one I'm curious about.
                      I'll try to get back to an experiment to see how much the AC resistance really differs from the DC resistance. It is mainly important to those who are interested in hi-Q TX oscillators.
                      I think that was what I was trying to get at.
                      -SB
                      OK.

                      The point I was trying to make was that the DC resistance will ALWAYS be the lowest as the voltage and current are always in phase in a DC circuit. Therefore even a frequency of 1 Hz will demonstrate an impedance higher than DC resistance (albeit only a tiny bit higher).

                      Luckily for us here were work our machines at quite low frequencies therefore many of the effects you mentioned do not come into measurable play....and we can usually safely ignore them.....(Helpful to me with my amateur level of analog electronics!)

                      Furthermore, as the current "lags" the voltage in a mainly inductive circuit, it also leads in a mainly capacitive circuit, but they are fully in phase with each other (current & voltage) when the circuit is at resonance, which gives us also maximum current for that capacitive/inductive circuit combination.....something needed for best search depth in a Tx coil. (this also gives optimum battery life with best power output.)

                      So it is VERY important for us all to keep this in mind.

                      Here is a web site that shows the above in a simple animated fashion:-

                      http://www.kwantlen.ca/science/physi...s/Phasors.html

                      Regards

                      Andy

                      PS. I love all your posts Simon, my posts are there to "add a bit on" to some of yours and to make things clearer for myself and others here.....never to upset you personally. Not as criticism, only discussion for all......

                      Comment


                      • Originally posted by der_fisherman View Post
                        OK.

                        The point I was trying to make was that the DC resistance will ALWAYS be the lowest as the voltage and current are always in phase in a DC circuit. Therefore even a frequency of 1 Hz will demonstrate an impedance higher than DC resistance (albeit only a tiny bit higher).

                        Luckily for us here were work our machines at quite low frequencies therefore many of the effects you mentioned do not come into measurable play....and we can usually safely ignore them.....(Helpful to me with my amateur level of analog electronics!)

                        Furthermore, as the current "lags" the voltage in a mainly inductive circuit, it also leads in a mainly capacitive circuit, but they are fully in phase with each other (current & voltage) when the circuit is at resonance, which gives us also maximum current for that capacitive/inductive circuit combination.....something needed for best search depth in a Tx coil. (this also gives optimum battery life with best power output.)

                        So it is VERY important for us all to keep this in mind.

                        Here is a web site that shows the above in a simple animated fashion:-

                        http://www.kwantlen.ca/science/physi...s/Phasors.html

                        Regards

                        Andy

                        PS. I love all your posts Simon, my posts are there to "add a bit on" to some of yours and to make things clearer for myself and others here.....never to upset you personally. Not as criticism, only discussion for all......
                        Good thoughts, and never worry about questioning any of my ideas, it is always helpful to discuss and debate -- I have a tendency to always rebut, but I also believe in totally open mind, correcting mistakes, realizing theories can change and evolve and only represent a way to look at experimental data and aren't the "truth". So I enjoy discussions no matter how lengthy. Your contributions are always welcome and valued as are everyone's (IMO).

                        Cheers,

                        -SB

                        Comment


                        • Hi all, I just put together a SilverDog kit IGSL TGSL and while running some initial checks I found that my -5v rail was only -3.2V.

                          I desoldered the anode of D4 and it measured -6.2v.

                          I resoldered it and started looking for shorts - found none.

                          I measured the resistance to gnd and other rails and there was nothing that indicates a short or semi-short.

                          I then started lifting IC's to see if one of them was dud and found that when I removed U4, the supply rail changed to -6.2V so I figured it was the IC.

                          To confirm this, I swapped U4 with U7 (they're the same) and the supply rail went back to -3.2V which proves that the IC is fine and there is some other reason.

                          So my question is this... Is this behavior normal? I'm suspecting that the -ve voltage generator that is supplied by the 7.3 kHz signal isn't capable of providing the necessary current, which may or may not be a fault.

                          Is -3.2V while the board is operating normal?

                          I'm working off this schematic FWIW:
                          http://silverdog.co.uk/shop/image/da...LTGSLcoils.JPG

                          Thanks

                          p.s. The board is drawing about 100ma from the 12V supply which I figure is normal.

                          Comment


                          • Originally posted by Farside View Post
                            Hi all, I just put together a SilverDog kit IGSL TGSL and while running some initial checks I found that my -5v rail was only -3.2V.

                            I desoldered the anode of D4 and it measured -6.2v.

                            I resoldered it and started looking for shorts - found none.

                            I measured the resistance to gnd and other rails and there was nothing that indicates a short or semi-short.

                            I then started lifting IC's to see if one of them was dud and found that when I removed U4, the supply rail changed to -6.2V so I figured it was the IC.

                            To confirm this, I swapped U4 with U7 (they're the same) and the supply rail went back to -3.2V which proves that the IC is fine and there is some other reason.

                            So my question is this... Is this behavior normal? I'm suspecting that the -ve voltage generator that is supplied by the 7.3 kHz signal isn't capable of providing the necessary current, which may or may not be a fault.

                            Is -3.2V while the board is operating normal?

                            I'm working off this schematic FWIW:
                            http://silverdog.co.uk/shop/image/da...LTGSLcoils.JPG

                            Thanks

                            p.s. The board is drawing about 100ma from the 12V supply which I figure is normal.
                            I would suspect transistors Q3 and Q4, make sure they are correct (not leads reversed) and are turning on and off fully (saturating). You could even try replacing in case one is out of spec. If the transistors look good, double-check resistors R25 through R28, make sure they are not wrong. If not wrong, you could try using smaller resistors to see if that pumps a little more current out.

                            I think 100 mA sounds about right for IGSL, at least near the upper range.

                            -SB

                            Comment


                            • check 4024 pin 14 is there have +U i have the same problem when draw PCB forget this pin is +

                              Comment


                              • check polarity of electrolytics


                                post good photo of the board

                                Comment

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