VLF null and frequency

[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.

[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]

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.

[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?

[manhunt47]

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

It was interesting, but of course I think it's true about the circuit of the receiver of the resonant series.


If this is true, the choice of the resonant frequency of the receiver is in relation to the transmitter's frequency It only relates to the initial phase difference, but sensitivity and noise and the impact of various metals are still vague.

[manhunt47]

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.

But I think it's not like that, and in fact it's a Band pass filter circuit, which I've plotted on.
As can be seen, at TX frequencies below the resonance frequency, RX 10338HZ is more like the LOW PASS circuit and reduces the amplitude of the output voltage Vin
And also caused the signal to retard the Vin signal relative to the Vrx signal
And at higher frequencies than the resonance Rx, this phase difference is reversed.

Regarding the diagram and shape of the received signal amplitude, there is no difference in the choice of the sender Tx frequency higher or lower than the resonant frequency of the receiver.
But this choice of frequency is higher or lower than the resonance frequency Rx in the phase difference between Vrx and Vin, which is positive or negative.
In fact, in the Cibola circuit, selecting the sender frequency above the RX receiver has caused the Vin signal to retard to Vrx.


You said ((((The advantages of this are obvious. Better discrimination, less interference from emi, better ground balance capabilities.))) Can you prove this because I think there is not much difference between the frequencies higher and lower than the receiver's resonance frequency

[manhunt47]

If anyone can put or introduce a metal detector other than Cibola, which is input series resonant receivers, it will be of great help.

[dbanner]

The point I tried to make is that when both Rx and TX are at same resonance, in other words two identical coils of same inductance and tune capacitor, and when they are at balance( nulled), their is no phase shift of the received signal( or negligible phase shift). Both Rx and TX are in phase with each other.
However when Rx and TX are at different resonant frequency, there is phase shifting. I am not math guru, but I am sure that the amount of phase shift can be precisely calculated. The variables would be inductance, resistance and capacitance of Rx and TX, along with the wavelength of the tx signal.
I repeat again, not one on forum can resolve this issue adequately.

[manhunt47]

The point I tried to make is that when both Rx and TX are at same resonance, in other words two identical coils of same inductance and tune capacitor, and when they are at balance( nulled), their is no phase shift of the received signal( or negligible phase shift). Both Rx and TX are in phase with each other.
However when Rx and TX are at different resonant frequency, there is phase shifting. I am not math guru, but I am sure that the amount of phase shift can be precisely calculated. The variables would be inductance, resistance and capacitance of Rx and TX, along with the wavelength of the tx signal.
I repeat again, not one on forum can resolve this issue adequately.

Hello dbanner
What was the type of device used in your testing (please refer to the device name and serial or parallel resonance circuit).
How was your coil structure?

[Koala]

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

are you sure

you can tune the IDX from a depth of 35 cm to close to 50 cm by changing the RX capacitor and still be able to ground balance. Great for YouTube videos of air test.

It was unstable, poor discrimination, worse than leaving it at the original 35 cm setting. You loose all the gained depth and possibly more although I never measured it as the coil was unusable for detecting with.

[manhunt47]

are you sure

you can tune the IDX from a depth of 35 cm to close to 50 cm by changing the RX capacitor and still be able to ground balance. Great for YouTube videos of air test.

It was unstable, poor discrimination, worse than leaving it at the original 35 cm setting. You loose all the gained depth and possibly more although I never measured it as the coil was unusable for detecting with.

Hello Koala
I did my own test with a TGSL device, which is parallel resonance type and I saw it by changing the Rx capacitor(Increase or decrease) This will cause the resonance frequency of the receiver Get away from transmitter frequency And this lowers the sensitivity and depth of the device But the stability of the device was increased by the distance between transmitter and receiver frequencies.
I have not worked on the IDX project to have accurate information about it, but with regard to the receiver, the parallel resonance is almost close to the TGSL response, and both structures are parallel, such as Raptor project.
In the IDX device, the transmitter frequency is 6600 Hz and the resonance frequency of the receiver is 4650 Hz, which I have shown in the simulation and diagram below.


Now pay attention to the frequency response and the phase of this circuit.
As seen, the frequency of the Tx is far from the frequency of the Rx, and in fact the Tx frequency is where the variation of the amplitude and phase is very low.
If the transmitter frequency approaches the resonant frequency of the receiver, it will increase the amplitude and phase changes of the received signal in the receiver, and in fact, we will see a higher sensitivity, but I think the probability of the oscillation of the device will increase.
All of the above is merely a review of the behavior of the receiver's part of the circuit and does not mention the effect of the loop type and how it is nulled.
In fact, all of the above explanations are based on the assumption that the loop is properly nullified

[manhunt47]

Hello
does anyone know why the photos I uploaded in the previous post have been removed from here ???

My photo upload site was https://imggmi.com

[Qiaozhi]

Hello
does anyone know why the photos I uploaded in the previous post have been removed from here ???

Nothing has been removed.
I suspect you have copy and pasted photos that exist only on your computer, and therefore they're not visible to anyone on the forum.
To correctly attach files to your post:
1. Select "Go Advanced".
2. Select "Manage Attachments".
3. Then select "Add Files", browse, and upload.

[kt315]

then give just direct links.

[dbanner]

With tgsl, the phase shift circuitry is specifically designed for the spread between tx and Rx, 20degrees or thereabouts.
Changing the spread messes up the stability and ground balance adjustment range of circuit.
Look at Nautilus dmc circuit. The tx and Rx are close together at 14 khz. The shifters are designed for this in mind. Very stable.
Now look at silver sabre plus circuit, almost same as Nautilus except for shifters before switching. Silver sabre tx and Rx have similar spread like tgs