frequency questions expert advice needed

[metal mania]

• I understand about coils due to that excellent book inside the metal detector best 25 quid I spent in a while. My question is this is it possible to have a variable frequency using a variable resistor on the board linked to the same on the coil.

[Qiaozhi]

• I understand about coils due to that excellent book inside the metal detector best 25 quid I spent in a while. My question is this is it possible to have a variable frequency using a variable resistor on the board linked to the same on the coil.

If the coil is connected in parallel with a tuning capacitor, then the transmit frequency is defined by this combination of components.
However, if you drive the LC circuit with a forced oscillator, you can adjust the frequency over a small range without causing excessive distortion to the waveform. Have a look at Page 225, Fig. 14.5. This is a simple example of a forced oscillator. You can adjust the TX frequency by replacing R21 with a trimmer.

[Tibuck19]

If the coil is connected in parallel with a tuning capacitor, then the transmit frequency is defined by this combination of components.
However, if you drive the LC circuit with a forced oscillator, you can adjust the frequency over a small range without causing excessive distortion to the waveform. Have a look at Page 225, Fig. 14.5. This is a simple example of a forced oscillator. You can adjust the TX frequency by replacing R21 with a trimmer.

How can I test the frequency of coils with out it being connected to a detector? I bought two used whites coil that are unknown to myself or the seller.

[kt315]

LOL. look http://www.geotech1.com/forums/showt...ester-of-coils
i will order a batch in near time. i do ALL you feeling yourself comfortly.

[Tibuck19]

LOL. look http://www.geotech1.com/forums/showt...ester-of-coils
i will order a batch in near time. i do ALL you feeling yourself comfortly.

That looks very handy! when is near time ????? id take one.