VLF null and frequency

[manhunt47]

I think I also have seen series resonant TX coil with parallel resonant Rx, in other words, the other way around from scenario above. Have a look at seabass schematic here somewhere in forum. Do advance search, it is here as project posted by someone in the past.
The 7 degrees phase shift in your plot is due to the LCR8 effect on Vrx.

Hello dbanner
The subject you mentioned (seabass schematic ) did not find me even in Advanced Search.
Your explanation for the cause of the phase difference between Vin and Vrx is entirely correct, but the point is, why is the reason for choosing these values of Lrx and Crx at this resonant frequency of the receiver?
And why is the higher resonance frequency of the transmitter Tx not selected and what is its effect?

[dbanner]

Two coils tuned "off" resonance with respect to one another, behave in effect like a filter , this incurres a phase shift of the received signal. If the Rx resonant frequency is higher than TX, then this would be low pass filter, causing a negative phase shift and vice versa.
I'm just postulating here, not sure.
In series resonant Rx, what you have is high pass filter, so the tx frequency would be above Rx resonance. The advantages of this are obvious. Better discrimination, less interference from emi, better ground balance capabilities.
I'm still walking on thin ice.

[dbanner]

Maybe when Rx resonant frequency is different from the tx freq., The Rx coil and cap act as a band filter(or high pass or low pass), resulting in a phase shift of Vin. The amount of phase shift dependent on the difference between the TX freq. and the cut off freq. of the filter.
I'm walking on thin ice here

[dbanner]

I think I also have seen series resonant TX coil with parallel resonant Rx, in other words, the other way around from scenario above. Have a look at seabass schematic here somewhere in forum. Do advance search, it is here as project posted by someone in the past.
The 7 degrees phase shift in your plot is due to the LCR8 effect on Vrx.

[manhunt47]

Now, the question is, what is the difference between the series resonance and the parallel with regard to frequency and phase responses?
Which are the better choices?
And what are the disadvantages of each?
Please answer these questions with a precise and accurate answer

[manhunt47]

Now let's answer the frequency and phase response of the Cibola circuit with the assumption that the transmitter frequency is 14300 HZ and the resonance frequency in the receiver is set to 10338 HZ.
Here, the frequency response and phase of the Vin signal are displayed in relation to Vrx and do not respond to the opamp behavior.


As you can see, the transmitter frequency is 14300 in Cibola, and in this case the Vin signal is 7 degrees behind the Vrx.


But if the sender frequency was 10330 Hz, which is the same frequency of the resonant circuit of the receiver, then the Vin signal to Vrx would not have any phase differences and would cause the maximum possible range to be transmitted to Vin

[manhunt47]

Hello again, everyone
Although I did not receive the correct answers from anyone, I would love to continue to do so in the hope of achieving better results.

Initially, the parallel resonance was checked and now I will investigate the resonance with your help.
For this research, the TESORO Cibola metal detector receiver has been used, which is a series resonant.
The simulated circuit as well as an ideal series resonant circuit are shown below.


Initially, I have shown the Vin signal at the input preamp relative to the Vrx caused by the Rx coil.
As you can see, the Vin range is slightly less than Vrx, and the phase is lowered to Vrx.



Also, the Vout signal is displayed at the output of the preamp as well as the Vin, and there is a delay between these two signals at 5 °, which is due to the preamp behavior.

[manhunt47]

Both TX and Rx coil are in same horizontal plane, so any current flow in Rx should be in phase with TX provided they are tuned to resonate at same frequency. But by changing Rx resonant frequency, the phase shifts, but why? And how can this be calculated accurately? Nobody say nothing of this fundamental issue.

Of course, this may not be so difficult to understand, but it has a hard calculation.
In the previous report in the raptor project, I showed that in the parallel resonant circuit, the preamp input voltage is taken from the two ends of the Crx capacitor, showing the signals, and as you can see, the preamp input voltage of Vin is approximately 90 degrees behind the Vrx voltage This is due to the resonance and voltage division of Crx and Lrx, but this is not all that, because the displacement of the coils on each other and the null adjustment also have a second effect on phase change and can change it.

[manhunt47]

Regarding spread between TX freq. and Rx resonant frequency, you have made keen observation. I asked same question as to how is this is calculated in theory, I mean the relationship between the 'off" resonant frequency spread and phases. Is it an arbitrary thing? Does it matter? It must affect the ground balance range(ability to adjust GB to reject ferrite in old tesoro, and discrimination, but why does resonant frequency of Rx with respect to TX freq. affect the phase relationship between the two, nobody can explain this mathematically.
RAPTOR designer must surely understand this subject expertly, to know what spread to implement, and corresponding phase shifting in schematic design.
Hence a circuit can be designed around any coil and vice versa

It may seem that the only effect of choosing the resonance frequency of RX is only to change the initial phase or phase range, which is compensated by changing the range of ground balance and is within the correct range!!!!!!!
But this does not seem to me to be the case because I tested that in the parallel resonant circuit, the sensitivity was lower by choosing frequencies far away from the TX transmitter frequency, but when the resonant frequency of RX is closer to the TX transmitter, it increases the sensitivity and depth of the penetration.
Also, I did not calculate anything here, just the difference in the choice of frequencies

[manhunt47]

recommended for reading before asking theoretical questions

No fun jokes
Perhaps you should have named your own name instead of the author

[manhunt47]

I suspect it may have to do with the cost efficiency of coil production on a large scale, obviating the necessity to match individual search coils to a particular detector, and the tolerance for precise nulling without affecting phases too adversely. It was an economic decision.
Now there is less of a deviation of performance between detectors of same model, and coils can be readily interchanged and also a greater variety of coils made available too.
Obviously some slight redesign of schematic would be needed. That's for the engineers. Manager always looking to cut costs and improve efficiency. Engineers operate the other way around. Sparing no expense in the pursuit of perfection.

Hello dbanner
Your idea was really interesting, maybe it's exactly like you say because in parallel resonance the Loop Null Adjustment is much harder than the series resonance .


And this makes the range of different loops in the parallel resonance very low, which is why the dominant new designs are based on the series resonance .

But the important thing is, which one provides better performance and greater sensitivity and better resolution? And proof of this is very important.
Because there is no Manager here

[dbanner]

Both TX and Rx coil are in same horizontal plane, so any current flow in Rx should be in phase with TX provided they are tuned to resonate at same frequency. But by changing Rx resonant frequency, the phase shifts, but why? And how can this be calculated accurately? Nobody say nothing of this fundamental issue.

[dbanner]

In the following, the frequency response and phase of the RAPTOR circuit are simulated and brought forth. As we see, at the resonant frequency, we have the highest amplitude amplitude in Vin.
And at resonance frequencies The VIN is 90 degrees behind the Vrx


Regarding this frequency response, I think that in the resonant frequency range, if there is noise, it is easily amplified and entered with a high amplitude, but in the other frequencies there is no increase in noise.


And the next thing is, I think the Vin signal range can change greatly with changes in L and C tanks.


And the other thing is that I think near the resonance frequency, the phase changes are also very severe and can break the resolution.


And the odd thing is why the frequency of the transmitter in the Raptor circuit is so close to the receiver circuit's resonant frequency ?????


But in Tesoro's TGSL metal detector, I think the distance between transmitter frequency and resonant frequency of the receiver circuit was much higher than that of RAPTOR.

Regarding spread between TX freq. and Rx resonant frequency, you have made keen observation. I asked same question as to how is this is calculated in theory, I mean the relationship between the 'off" resonant frequency spread and phases. Is it an arbitrary thing? Does it matter? It must affect the ground balance range(ability to adjust GB to reject ferrite in old tesoro, and discrimination, but why does resonant frequency of Rx with respect to TX freq. affect the phase relationship between the two, nobody can explain this mathematically.
RAPTOR designer must surely understand this subject expertly, to know what spread to implement, and corresponding phase shifting in schematic design.
Hence a circuit can be designed around any coil and vice versa

[kt315]

Please answer my questions if possible and someone has the opportunity

recommended for reading before asking theoretical questions

[dbanner]

I suspect it may have to do with the cost efficiency of coil production on a large scale, obviating the necessity to match individual search coils to a particular detector, and the tolerance for precise nulling without affecting phases too adversely. It was an economic decision.
Now there is less of a deviation of performance between detectors of same model, and coils can be readily interchanged and also a greater variety of coils made available too.
Obviously some slight redesign of schematic would be needed. That's for the engineers. Manager always looking to cut costs and improve efficiency. Engineers operate the other way around. Sparing no expense in the pursuit of perfection.