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Cable connected to the coil will have small but finite effect on coil performance. Adding 1.5 or 1.8m of coax will add some capacitance, like 150-200pF for common cable types, to other circuit capacitances, but you well may not notice that. This added capacitance will slow down coil a bit, but not dramatically, will change SRF somewhat lower, and if you want to tune detector “on knife edge” small variation of dumping resistor value is needed. No need for some exotic cable types etc. for this coil.
Best way to adjust detector is with cable, shield and all in place, then you can optimize Rdump value and minimal sampling delay.
10” coin range is not good at all. In order to utilize full potential of this coil, minimal sampling delay must be set, then all advantage is from this shorter delay compared to standard coils, increased sensitivity to small objects\gold, larger “coin” range etc, no other magic involved.
If you have scope, this adjustment is simple, if not, try iterative way.
First, set Rdump to some convenient value, like 330R, set delay pot. to minimum, adjust delay trimmer (reduce resistance) to the point when detector stops responding, if needed, change component values to get that point, then increase delay just a bit above this to get response. Delay now will be around or below 10uS.
Then try to tweak Rdump value. Reducing it will overdump the coil, delay will increase and at some value detector will again stop responding, so you need to increase delay a bit to get response. This is too low value. From this point, goal is to increase Rdump to the point when minimal delay adjustment can be achieved, but not above that. Too large Rdump value will underdump the coil, some ringing will appear on waveform, but you wont notice that in air tests, analog detectors are very tolerant. However, in ground tests, significant ringing will produce some instability and loss of range.
Use some pot. or trimmer for this rdump adjustment, then, when you find optimal value, replace with resistor(s) to within 5% of measured value.
If everything is done right, outdoors tested on battery power, you have to achieve like 11-12” for small gold ring, 13-14” for coin (18mm 1E) or better.
Please note that this ranges are not guaranteed or absolute, may vary in different designs due to different PCB layouts, noise problems (7660 synced or not etc), component quality\type, and other factors, so i not claim that every construction or kit will work like this.
Best way to adjust detector is with cable, shield and all in place, then you can optimize Rdump value and minimal sampling delay.
10” coin range is not good at all. In order to utilize full potential of this coil, minimal sampling delay must be set, then all advantage is from this shorter delay compared to standard coils, increased sensitivity to small objects\gold, larger “coin” range etc, no other magic involved.
If you have scope, this adjustment is simple, if not, try iterative way.
First, set Rdump to some convenient value, like 330R, set delay pot. to minimum, adjust delay trimmer (reduce resistance) to the point when detector stops responding, if needed, change component values to get that point, then increase delay just a bit above this to get response. Delay now will be around or below 10uS.
Then try to tweak Rdump value. Reducing it will overdump the coil, delay will increase and at some value detector will again stop responding, so you need to increase delay a bit to get response. This is too low value. From this point, goal is to increase Rdump to the point when minimal delay adjustment can be achieved, but not above that. Too large Rdump value will underdump the coil, some ringing will appear on waveform, but you wont notice that in air tests, analog detectors are very tolerant. However, in ground tests, significant ringing will produce some instability and loss of range.
Use some pot. or trimmer for this rdump adjustment, then, when you find optimal value, replace with resistor(s) to within 5% of measured value.
If everything is done right, outdoors tested on battery power, you have to achieve like 11-12” for small gold ring, 13-14” for coin (18mm 1E) or better.
Please note that this ranges are not guaranteed or absolute, may vary in different designs due to different PCB layouts, noise problems (7660 synced or not etc), component quality\type, and other factors, so i not claim that every construction or kit will work like this.
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