Changing frequency on a metal detector

[lamarc]

IF wanted to change frequency on a metal detector say from 18khz down to 13khz or say switch on to another by a switch how could you do it. Thanks Lamar

[Carl-NC]

With some effort, you could probably could, especially going lower. Some detectors derive audio tones off the TX frequency, so they might shift as well.

You would need to see whether the frequency is set by a crystal, or a passive oscillator that uses the TX coil (i.e., Colpitts or Hartley). If a crystal, then the coil will need to be wideband or retuned. If passive, then just tune down the osc. using additional capacitance. RX coil may also need retuning.

- Carl

[lamarc]

Thanks Carl

Thank for the info the detector I am referring to is a xp-goldmaxx running on 18khz. I can pick up a nickle at 15 inches air testing.By lowering the khz say to maybe 7.5 or some what would give me more depth.It already has a stock 9 inch dd stock coil. Lamar

[lamarc]

Thanks Carl

Thank for the info the detector I am referring to is a xp-goldmaxx running on 18khz. I can pick up a nickle at 15 inches air testing.By lowering the khz say to maybe 7.5 or some what would give me more depth.It already has a stock 9 inch dd stock coil. Lamar

[Carl-NC]

I don't know anything about that detector, so I can't offer any more guidance.

- Carl

[Radioactive]

As Carl said, The oscillator is fixed with a cap or resistor. I have replaced the fixed cap with a variable one to shift the frequency, but you can only shift it a few Hz high or low. Some use a crystal oscillator, so you would need to change or replace the crystal frequency. Now as every good RF Eng. knows, it is easer to move higher then lower in frequency. You want to move it more than 50% of the fundamental frequency, thats a big deal. (18 KHz. to 7 KHz.)
Now, if it uses a 555 as an oscillator, you can change the frequency a lot, you have to look at the circuit. You have to remember that you will need to move the receiver also, then you will need to change the coil. You will need to change so much, you need to start from the ground up. Remember it's a balanced circuit. Good Luck.

[lamarc]

Well I better leave well enough alone because

air testing a nickle at 15 inches with a good hit is not bad. Thanks Lamar