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Offline scout119Topic starter
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« on: June 29, 2010, 12:28:56 pm »
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Hello,

I hope someone can point me into a right direction with this. I am building bfo detector and would like to measure frequency of the search coil.

1. Is there a way to do that without oscilloscope or frequency counter?
2. How to measure it with oscilloscope (never used one before)?

Thanks in advance!

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Offline GoldDigger1950
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« Reply #1 on: June 29, 2010, 12:51:24 pm »
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A coil by itself and its inductance is not a measurement that independently affects its frequency of operation. It requires a capacitor in order to be frequency dependent. That being said, there are optimum coil inductance measurements for a range of frequencies which would be helpful to know in designing a coil. The reason for that is again dependent upon the capacitance in the rest of the design. The combination of a coil and capacitor make a tuned circuit called a tank circuit. This circuit will determine the actual frequency of operation.

In short, the coil is only half of the components that determine frequency.

You can measure the operating frequency of a tuned tank circuit using an LCR meter and applying your measurements to a formula. An oscilloscope is not needed.

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« Last Edit: June 29, 2010, 12:54:22 pm by GoldDigger1950 »
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« Reply #2 on: June 29, 2010, 12:58:02 pm »
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Thank you GD,

I guess I should have mentioned that I am using this design

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http://www.easytreasure.co.uk/bfo.htm


I am just trying to make sure my coil will work, before i will "seal" it in its assembly.

Thanks


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Offline GoldDigger1950
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« Reply #3 on: June 29, 2010, 01:07:17 pm »
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If you wound the coil according to the designer's specification, it should be fine. Looking at the spec and overall design at your link, I note that tuning is by the "seat of your pants" rather than design accuracy. Just build it, try it and worry later if it doesn't function right. I know that sounds a bit shonky but my advice is down to the loose design parameters of that circuit. Don't seal the coil until you're satisfied with its workings.

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« Reply #4 on: June 29, 2010, 01:20:30 pm »
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Make sense.
Thank you for your opinion.

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