3 dB down and coil Q VS bandwidth

[dbanner]

In the "off resonance" type of IB coil, what are the Parameters of the RX coil which are important to the overall selectivity of the search coil, and what if the resonant frequency of the RX tuned with parallel C fall outside of the 3 dB down bandwidth as seems to be the case with most all "off resonance" designs?

Despite the coupling efficiency of the Rx coil, it seems to be tuned to some Harmonic resonance outside of the 3 dB down bandwidth, but why?, and not just an arbitrary value. Anyone have experience in this area of coil design parameters?

[dbanner]

I have done some thinking on harmonization of frequencies based on the notes of the musical scale, namely E-F-G-A-B-C-D-E
Now here I suspect some similarities, so I octaved up the standard notes of the musical scale to the band of the IB detectors, and I was amazed. If one is familiar with musical scales, in particular the Harmonic minor scales, you will see that the third, fifth, seventh etc. all harmonize with the first note (fundamental (f) of that scale.
Now I wonder if there are some clues to the way "harmonic resonance" otherwise known as "off resonance" coils are designed for best performance characteristics.

[dbanner]

Now if you look at the table I posted, If you take C at 4168 hertz, and the fifth note of the C scale,which is G at 6271 hertz, you can see Whites coil. (6590-6271=319), so increase 4168 by 319 you get 4487 hertz.
In other words, make G 6.59kHz, then use same notal relationship to C and you will get 4.5kHz, exactly the Tx and Rx of the whites coil.

So in the whites coil, perhaps Rx frequency of 4.5kHz represents the fundamental(f) and 6.59kHz is the fifth. The two frequencies harmonize!

[Nandor]

Very interesting conclusion!

What about Tesoro, were Tx is lower than Rx.

[dbanner]

Very interesting conclusion!

What about Tesoro, were Tx is lower than Rx.

.
Look at G on table at 12543 hertz and A at 14080 hertz
Now make G 14543 hertz and so A becomes 14080+2000=16080 Hertz! There it is, the tesoro frequencies for TGSL! Tx 14.5kHz, Rx 16.1 kHz.
Remenber that all 3rds, 5ths, 7ths harmonize with (f), so if 16.1kHz represents (f), then 14.5kHz would represent the seventh note in the A scale, which would harmonize with (f).
All I am doing is shifting the notes by equal magnitudes to maintain the same musical notes seperation.

[dbanner]

In the musical scales, A is at 440 hertz relative to middle C. But you could make A any frequency, while maintaining the same octave spread between notes.
The point is that I am applying the same principles of notal harmonics to see if there is anything similar to "off resonance" coil frequency relationships.
Maybe walking down a blind ally, but somehow I have the feeling that all these matters are interconnected, such is the beauty of the universe.

[dbanner]

Now the seventh harmonic is weaker than the fifth, so the tesoro Rx coil Q is less than the Whites. The tesoro Rx may have a wider bandwidth. I wish I could run all the numbers, but my math is poor.

[Nandor]

This reminds me of my first search coil, I was tuning it and there was a frequency were the TGSL had very good sensitivity but I could not adjust GB properly, maybe it was the 5th harmony of TX 14,6kHz. The 20 degrees phase shift for TGSL does not allow it, maybe with some phase shifter modification TGSL could work with 5th harmony RX.

I like your topics man!

[bbsailor]

I have done some thinking on harmonization of frequencies based on the notes of the musical scale, namely E-F-G-A-B-C-D-E
Now here I suspect some similarities, so I octaved up the standard notes of the musical scale to the band of the IB detectors, and I was amazed. If one is familiar with musical scales, in particular the Harmonic minor scales, you will see that the third, fifth, seventh etc. all harmonize with the first note (fundamental (f) of that scale.
Now I wonder if there are some clues to the way "harmonic resonance" otherwise known as "off resonance" coils are designed for best performance characteristics.

Here is a little more insight to musical scales. Look up the 12th root of two or what number multiplied by itself 12 times will give you the number 2. There are 12 tones in a musical scale and the octave is at twice the frequency as the fundamental, thus the number 2. Look at the fret board on a guitar and see that each fret going up the neck gets slightly closer together. At the 12 th fret the string is half as long and at twice the frequency as the open string frequency.

One more interesting thing about fret spacing is that is a good visual reference to compound interest. The rule of 72 states that if you divide the interest rate return into 72 you will see how long it takes to double your money.

Thus we have harmonics in electronics, music and money.

Joseph J. Rogowski

[dbanner]

Here is a little more insight to musical scales. Look up the 12th root of two or what number multiplied by itself 12 times will give you the number 2. There are 12 tones in a musical scale and the octave is at twice the frequency as the fundamental, thus the number 2. Look at the fret board on a guitar and see that each fret going up the neck gets slightly closer together. At the 12 th fret the string is half as long and at twice the frequency as the open string frequency.

One more interesting thing about fret spacing is that is a good visual reference to compound interest. The rule of 72 states that if you divide the interest rate return into 72 you will see how long it takes to double your money.

Thus we have harmonics in electronics, music and money.

Joseph J. Rogowski

bbsailor, just what the heck are you trying to say?


If I learn to play guitar and study electronics, I will become rich because of the harmonic relationship between the three?

You confuse me....

[bbsailor]

I have done some thinking on harmonization of frequencies based on the notes of the musical scale, namely E-F-G-A-B-C-D-E
Now here I suspect some similarities, so I octaved up the standard notes of the musical scale to the band of the IB detectors, and I was amazed. If one is familiar with musical scales, in particular the Harmonic minor scales, you will see that the third, fifth, seventh etc. all harmonize with the first note (fundamental (f) of that scale.
Now I wonder if there are some clues to the way "harmonic resonance" otherwise known as "off resonance" coils are designed for best performance characteristics.

Here is a little more insight to musical scales. Look up the 12th root of two or what number multiplied by itself 12 times will give you the number 2. There are 12 tones in a musical scale and the octave is at twice the frequency as the fundamental, thus the number 2. Look at the fret board on a guitar and see that each fret going up the neck gets slightly closer together. At the 12 th fret the string is half as long and at twice the frequency as the open string frequency.

One more interesting thing about fret spacing is that is a good visual reference to compound interest. The rule of 72 states that if you divide the interest rate return into 72 you will see how long it takes to double your money.

Thus we have harmonics in electronics, music and money.

Joseph J. Rogowski

[dbanner]

Maybe I will table out the frequencies of the octaves of all twelve notes (whole tones and semitone steps) to include the sharps and flats etc. between say 5kHz and 30kHz. So I can have a reference.

Then explore the coil Q and bandwidth parameters with specific reference to off resonance coils. I have a feeling the ambient temperature must have something to do with getting the Rx to respond in the linear region, such that the sensitivity does not drop off sharply with temp variations. But picking a harmonic frequency for the off resonance spread might be beneficial to the whole thing. I simply do not know why.
All this requires going back to math school. I forgot all those bode diagrams techniques long time ago.

[Nandor]

Maybe I will table out the frequencies of the octaves of all twelve notes (whole tones and semitone steps) to include the sharps and flats etc. between say 5kHz and 30kHz. So I can have a reference.

Then explore the coil Q and bandwidth parameters with specific reference to off resonance coils. I have a feeling the ambient temperature must have something to do with getting the Rx to respond in the linear region, such that the sensitivity does not drop off sharply with temp variations. But picking a harmonic frequency for the off resonance spread might be beneficial to the whole thing. I simply do not know why.
All this requires going back to math school. I forgot all those bode diagrams techniques long time ago.

Watch this, Mark Rowan talks about Tx frequency from 04:00 mins. "https://www.youtube.com/watch?v=87PL...6C53B3&index=8"

Calculating frequencies would be enough fom 5kHz-20kHz I think. As almost everybody looks for silver which likes low frequency, thats why IDX is more sensitive on silver and brass that TGSL.
Maybe the TGSL on a lower frequency and at 5th harmonic with 20 degree shift would be more sensitive too.

[dbanner]

I'll have a look at that video.

The silver sabre uses the same coil and is nearer to 12kHz I think. You could modify the TGSL to operate at the lower frequencies(below say 10kHz) .Maybe by using a Rx of say 8.5Khz and then de-tuning the Tx down until you can achieve the 20 degrees phase offset.
I saw nice online software for calculating values of components in active filters(op-amps). Analog Devices Filter Wizard.https://www.google.com/url?sa=t&rct=...vXSSK_SfOb4jj6

[Nandor]

How interesting I just have read the Silver Sabre topic .

Happily th TGSL has Differential pre amp so its easy to set another frequency, we know that it can run at 8kHz but what about 6 or 7 kHz? I have a modified version TGSL with Minelab Oscillator and other stuff it pretty tolerant.

I have to make some test again with it, I also made Golden Mask type coil with Tx 1mH and Rx 6.5mH. That would do, but I just don't know how to get good Rx frequency if i tune it for 7kHz. Sound would be low but the voltage converter should do fine.