The Mighty "Fisher CZ5 Quicksilver" and it's secrets

[ivconic]

As so far none of you have been able to imagine this even in your sleep; I don't like math, formulas, calculations, graphs, simulations ... blah!
It's like a pesticide for me.
If anyone cares about my presence on the topic; it is enough to start publishing formulas, calculations, graphs and simulations ... and I will disappear in the form of a quiet fart!
We call it the "silent pigeon" here!

[Carl-NC]

It's common for the channel filters to have a bandpass element and a notch element. In the CZ design the LF channel has a notch filter but the HF channel does not. I don't know why except that maybe the LF channel needs to be cleaner. In the White's V3 the channel filters were strictly BP and channel cross talk was a problem for ground tracking.

[dbanner]

Maybe this particular band pass filter has low Q and limited rejection of the second or third harmonic, hence the notch(reject) filter?
In the HF channel, the harmonics are of no consequence( besides which, they are very weak to begin with because they are 4th and 5th) and so a notch isn't required?

[dbanner]

I have this scope picture, it looks same as Carl's graphics. I think it's from dfx?

[Carl-NC]

Yes, that's identical to the DFX. It's also identical to one of the modes on the new XP Deus II because it is a very balanced waveform for a 5th harmonic system. The DFX is 3+15 kHz, the Deus II is 7.5+37.5 kHz.

[dbanner]

Hmm, so these pulse trains are such that they seek to modulate the current in the coil such that optimization of the fifth harmonic is achieved?
This is a prerequisite for a fifth harmonic system.

[Riss]

This was my attempt at multi-frequency. I lost interest when the Equinox was introduced and later the Vanquish. But now may revisit the project after a long rest.

It worked pretty good, but was weak on the low conductors. The gain in the harmonic channel needs to be increased to equalize the gain between high and low conductors.

I used the CZ timing as a model, 5khz & 15khz generated by a cheap pic18f1220. It uses a full bridge tx driver to gain the extra coil current. The tx driver is straight from the ML Sovereign. The the rest of the circuit is standard analog. It ignores salt water and has manual ground balance.

Necessary from a notch filter in a channel 5kHz is directly related to this , that there is a 30 degree phase shift (this is no accident - exactly 30 degrees ) between the oscillogram of 5kHz which goes to the coil driver and the one that goes to MAX333 ( 4053 ) for phase detection in a channel ALL METAL (eliminated soil effect , ground reject - in it the ferrites have a very weak positive reaction ).

[Carl-NC]

Hmm, so these pulse trains are such that they seek to modulate the current in the coil such that optimization of the fifth harmonic is achieved?
This is a prerequisite for a fifth harmonic system.

Yes, the goal is to maximize the fundamental & 5th, and minimize other harmonics.

[dbanner]

This is the reject filter?

[Carl-NC]

Yes, twin-T notch filter.

[Qiaozhi]

Yes, twin-T notch filter.

The notch is tuned to 14.5kHz ... and it's in the 15kHz channel. Does that make any sense?

[Altra]

Maybe there was/is an interfering terrestrial or man made Vlf signal at 14.5khz when the CZ was designed? Or as Riss mentioned, maybe for phase correction? The DFX schematic Dbanner posted uses no notch filters.

Lots of vlf out there.

http://www.vlf.it/

[Altra]

Necessary from a notch filter in a channel 5kHz is directly related to this , that there is a 30 degree phase shift (this is no accident - exactly 30 degrees ) between the oscillogram of 5kHz which goes to the coil driver and the one that goes to MAX333 ( 4053 ) for phase detection in a channel ALL METAL (eliminated soil effect , ground reject - in it the ferrites have a very weak positive reaction ).

You'll have to ask Dave Johnson about the notch filters purpose. My circuit uses no notch, I adjust the phase of the LF and HF separately to reject pure ferrite signal. Then mix the XL, XH, RL, RH to achieve salt balance and broad range GB.

[dbanner]

So if maximum elimination occurs at centre frequency fC = 1/(2πRC)
From the schematic, I take the value of C=2200pF and R=4990r
Result is 14.5khz. uh? Isn't it meant to be a 15khz notch?
With values from schematic, assuming they are correct, f-low @10.5khz and f-high @17.5khz

But why not just make centre frequency 15khz already? Maybe choices limited by E standard capacitor and resistor values? Maybe Fisher engineer designed the circuit for values already on hand. Let's just use those 2.2's caps and 4.99k's. we have plenty of those. We'll still be within the bandstop region, good enough for Ohio.

[dbanner]

discreet RX preamp of cz6 is also imparting a phase shift. Yes?