Frequency Shift And Doubts On It

[Skull diver]

I recently stumbled upon the use of the mono program by accident and noticed a lack of a specific data point in the mf programs.

Although I understand the minimal variation in frequency multiples and the almost no importance other than to clean the signal from interference, I still noticed that between shift 0 and shift 6, the frequency can slip a lot.

In my case, I suffer in saltwater from a difficulty in finding a sweet spot between 24 and 40 kHz or at least visualizing the actual setting.

This is quite different from the autotune scan, believe me.

I am referring to the lack of an exact kHz number that I justify with more frequencies working, but that does not help in understanding what level you are working at.

If I take into account in mono 40 kHz with a 0 shift, I assume I am reaching about 32 kHz.

In mf this should translate the same way with the unknown of the lowest frequency.

There are missing pieces in this theory but the lack of the number of kHz relative to the shift in use does not help me.

[Chase Goldman]

13 hours ago, Skull diver said:

I recently stumbled upon the use of the mono program by accident and noticed a lack of a specific data point in the mf programs.

Although I understand the minimal variation in frequency multiples and the almost no importance other than to clean the signal from interference, I still noticed that between shift 0 and shift 6, the frequency can slip a lot.

In my case, I suffer in saltwater from a difficulty in finding a sweet spot between 24 and 40 kHz or at least visualizing the actual setting.

This is quite different from the autotune scan, believe me.

I am referring to the lack of an exact kHz number that I justify with more frequencies working, but that does not help in understanding what level you are working at.

If I take into account in mono 40 kHz with a 0 shift, I assume I am reaching about 32 kHz.

In mf this should translate the same way with the unknown of the lowest frequency.

There are missing pieces in this theory but the lack of the number of kHz relative to the shift in use does not help me.

In fast multifrequency (FMF) two things are in play for salt water detecting - FMF allows you to more easily compensate for salt balance, you can't do that in mono frequency.  Second, you are confusing the FMF maximum frequency setting (14 kHz, 24 kHz, or 40 kHz) with the mono-frequency adjustment bands.  I don't fault you because XP's explanation in the manual sort of conflates these Mono and FMF when talking frequency bands. The FMF maximum frequency setting basically gives you a rough cutoff of the upper frequency of a continuous spectrum of simultaneous frequencies that is weighted accordingly either high or low based on the maximum frequency you choose.  So the mono frequency shifts listed in the "Range of available frequencies" listing are meaningless as far as FMF modes are concerned.  Here is further explanation from the manual:

Range of available frequencies of 4 kHz to 45 kHz :
4.08 to 4.76 kHz - 6.94 to 8.08 kHz - 10.39 to 15.15 kHz - 15.62 to 20.75 kHz
22.06 to 28.57 kHz - 29.41 to 35.32 kHz - 36.36 to 45.45 kHz

Remember  that  generally  all  frequencies  detect  all  targets,  but  a  high  frequency  such  
as  45  kHz  will detect  a  far  greater  proportion  of  small  targets  than  low  frequency  
like  4  kHz,  above  all  if  the  ground  is mineralized. Conversely, a high frequency will 
sometimes be less efficient on a large mass or on grouped coins than a low frequency. The best 
option is therefore to use  the Deus 2  on its simultaneous programs as a priority, to 
make the most of an extended range of frequencies and thus maintain sensitivity to a wider range of 
targets.

To help you better adapt to your soil and desired targets, the   Deus 2   offers you the 
possibility to limit the [multi] frequency  band  used  from  above.  For  example  :  You  can  configure  
your  machine  with  24kHz  limit  to  be less sensitive to very small conductors and more stable 
in difficult ground conditions. Selecting the 14kHz limit can help focus on high conductors while 
reducing the crackling from some ferrous targets. Selecting the 40kHz limit will remain the most 
versatile option because it selects the widest frequency range, which will  be  more  sensitive  to 
 a  wider  range  of  targets,  non-ferrous  targets  close  to  ferrous  and  better  performance on some mineralized ground.

[My note:  You can't shift these FMF maximum frequency limits, nor should you really need to because you are in FMF]

Program no. 7 Mono can be useful if the multi-frequency programs are hampered by a severe 
electromagnetic environment or if you prefer to focus on a particular target category.

No detector manufacturer that markets a simultaneous multifrequency detector goes into much detail on the individual frequencies transmitted to create the multifrequency spectrum.  You get a lot less specifics from ML regarding any frequencies used in Multi IQ and Nokta also does not give much in the way of frequency specifics but does give pretty good descriptions of the different "M" weightings of their various multifrequency modes.   At least XP is providing the FMF cutoff frequency and allowing you to adjust it on a mode-for-mode basis even if it is only three break points.  No other manufacturer allows you to further customize simultaneous frequency modes in this manner.  What is not known, however, is whether you are actually adjusting the D2 transmitted multifrequency spectrum by selecting this parameter, or limiting target signal processing to those targets detected by transmitted frequencies below the cutoff (while the full spectrum of transmitted frequencies continues be sent into the ground). I personally don’t care as long as it works, similar to the fact that I don’t know or care what or how many actual discrete frequencies are simultaneously transmitted by Nox, Manticore, Legend, or the D2.  I simply apply those 3 FMF cutoff frequencies appropriately as the situation demands consistent with the XP manual description above.
 

[Sinclair]

On 1/21/2024 at 2:19 AM, Skull diver said:

If I take into account in mono 40 kHz with a 0 shift, I assume I am reaching about 32 kHz.

As Chase quoted from the manual, I think Shift 3 represents the selected "master" frequency. 32kHz Shift 3 = 32kHz, Shift 0 = 29,41 and Shift 6 = 35,32. 40,5kHz Shift 3 = 40,5kHz, Shift 0 = 36,36kHz, Shift 6 = 45,45kHz and so on...

As far as I remember, some russians analyzed the frequency spectrum with an oscilloscope somewhere on youtube.

[Skull diver]

1 hour ago, Sinclair said:

As Chase quoted the manual, I think Shift 3 represents the selected "master" frequency. 32kHz Shift 3 = 32kHz, Shift 0 = 29,41 and Shift 6 = 35,32. 40,5kHz Shift 3 = 40,5kHz, Shift 0 = 36,36kHz, Shift 6 = 45,45kHz and so on...

As far as I remember, some

I cannot comment on whether the shifts match the mono program frequencies, partly because in MF the low frequency or at least lower than the cut off @ 40kHz also interacts.
However, I can assume with certainty that 40Khz "max" in shift 0 is much less chatty than on shift 6.
Immersed in salt water there is no EMI that can justify this behavior other than the direct reaction of saline, on the kHz increase.

[Skull diver]

4 minutes ago, Skull diver said:

, I think Shift 3 represents the selected "master" frequency.

I neglected to mention this aspect....
I must have forgotten the lowering of about 3 kHz on 0 and the raising of as many 3 kHz on 6.
According to this concept, on shift 3 you set the real maximum frequency of 14/24/40 kHz.
(The coupled low frequency still remains invisible in the setting.)

[Sinclair]

I don't know, if FMF shifts the frequencies excactly like Mono, but over all "masters" simultaneously - that has to be checked with an oscilloscope - don't have one atm. Perhaps it works with a microphone and audio analyser, too? 🤔

But I think now I get what you mean.. the Mono "masters" do not match the Max Freq. Settings in FMF.
Aka Mono "masters" are 5 – 7.5 – 13 – 17.6 – 25 – 32 – 40.5 kHz - but FMF Max Settings are 14, 24, 40kHz.

[Chase Goldman]

The Mono master or core frequencies are almost certainly unrelated to the FMF cutoff/Max frequencies and the shift ranges. 

No one has been able to actually satisfactorily explain to me what shift/noise cancel/EMI cancel channel adjustments actually do in terms of how they affect the entire transmitted FMF/Multi-IQ/SMF spectrum of any SMF detector (D2/Nox/M-Core/Legend).  There is a lot of incorrect conflation of SMF channel shifting with Mono/Single Frequency shifting in general (i.e., not just limited to Deus 2 users) and I am not sure if FMF/SMF noise cancel channel shifts really adjust the transmitted frequency spectrum (like it does on Mono) vs. just target signal receive/input "circuit" filters.   This is something that a detector design engineer like @Geotech can perhaps better explain in terms of general methodologies.

The only thing I do know is FMF shift is just the manual version of automatc FMF noise cancel to select a quiet "channel" 0 thru 6, with 3 as middle default setting.  By design for both Mono and FMF, shift is meant to be an incremental adjustment for EMI suppression (you can see from the Mono shift ranges that the ranges increase with the higher frequencies but are still small based on percentage change from the base frequency) and is not intended to appreciably affect target detection performance (other than respect to increasing the signal to noise ratio) nor is FMF channel shift definitely tied to or equivalent to Mono Frequency shift ranges from what I can tell.

[Skull diver]

5 hours ago, Sinclair said:

But I think now I get what you mean.. the Mono "masters" do not match the Max Freq. Settings in FMF

True.

And We can only take note of the frequency limit choosing 14/24/40 as the max setting.

 

[Geotech]

2 hours ago, Chase Goldman said:

No one has been able to actually satisfactorily explain to me what shift/noise cancel/EMI cancel channel adjustments actually do in terms of how they affect the entire transmitted FMF/Multi-IQ/SMF spectrum of any SMF detector (D2/Nox/M-Core/Legend).

The TX frequencies are proportionately adjusted by some small amount. For example, Park mode on the Equinox nominally runs at 2.6/7.8/39 kHz which is a ratio of 1:3:15. Let's say that the next channel up from that is a 2% shift; the frequencies will now be 2.652/7.956/39.78 kHz, which is still a ratio of 1:3:15. That's what I mean by "proportionately adjusted," the ratios never change. The total adjustment range is usually small, no more than maybe +/-10%, which isn't enough to cause any major difference in performance.

Here is a scope probe of the mid-channel waveform (bottom) and the highest channel waveform (top) for the Eq800. You can see that they "look" identical except that the high channel is slightly compressed, by 2.5%. It's like an accordion bellows.

I have no idea what the D2 does in its frequency limit feature, I don't have one to test.

 

[Chase Goldman]

Just now, Geotech said:

The TX frequencies are proportionately adjusted by some small amount. For example, Park mode on the Equinox nominally runs at 2.6/7.8/39 kHz which is a ratio of 1:3:15. Let's say that the next channel up from that is a 2% shift; the frequencies will now be 2.652/7.956/39.78 kHz, which is still a ratio of 1:3:15. That's what I mean by "proportionately adjusted," the ratios never change. The total adjustment range is usually small, no more than maybe +/-10%, which isn't enough to cause any major difference in performance.

Here is a scope probe of the mid-channel waveform (bottom) and the highest channel waveform (top) for the Eq800. You can see that they "look" identical except that the high channel is slightly compressed, by 2.5%. It's like an accordion bellows.

I have no idea what the D2 does in its frequency limit feature, I don't have one to test.

 

Thanks Carl, I was hoping you'd chime in on this because what actually happens on this FMF/Multi-IQ/SMF channel shift thing has been a mystery to me for awhile.  Bottom line: as long as the shift between channels is relatively small and the discrete frequency ratios are maintained you can mitigate interference with little impact to performance similar to single frequency shifts for noise mitigation.