Transmit frequencies and Noise Cancel

[cudamark]

This may be better suited for the tech talk section, but, I thought I would try here first. I'm curious as to how the noise cancel setting might change depth and/or sensitivity on certain metals. My understanding (limited as it is) is that the noise cancel settings shift the transmit frequencies (slightly according to Minelab) to help find one that has less interference where EMI is present. Fine, but, lets say that you're in an area without any EMI, so, finding a quiet setting is moot. Is there a manual setting that would be better for depth? Better for silver or gold? How much of a frequency shift is actually happening here? For instance, if you were in say 15khz, would changing from -9 to +9 make the machine go from 14khz to 16khz? The other way around? More or less effect than that? Does the frequency mix in Multi change? If so, in what way does it change in each mode? Has anyone run any tests on this? I know, I should just go detect and not ponder such weighty questions, but, I can't help myself!

 

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[vferrari]

This may be better suited for the tech talk section, but, I thought I would try here first. I'm curious as to how the noise cancel setting might change depth and/or sensitivity on certain metals. My understanding (limited as it is) is that the noise cancel settings shift the transmit frequencies (slightly according to Minelab) to help find one that has less interference where EMI is present. Fine, but, lets say that you're in an area without any EMI, so, finding a quiet setting is moot. Is there a manual setting that would be better for depth? Better for silver or gold? How much of a frequency shift is actually happening here? For instance, if you were in say 15khz, would changing from -9 to +9 make the machine go from 14khz to 16khz? The other way around? More or less effect than that? Does the frequency mix in Multi change? If so, I what way does it change in each mode? Has anyone run any tests on this? I know, I should just go detect and not ponder such weighty questions, but, I can't help myself!

ML has provided no documentation on how they do it. It could be a combination of a slight frequency shift (as stated in the manual) and possibly a change in filters used in target signal processing. However they do it, it is most likely designed to not change the characteristics of the search mode profile (Park, Field, Beach, Gold, etc.) or single frequency setting for which you are doing the noise cancel. ML does state that pinpoint is affected by the noise cancel setting, but doesn't say how. If they actually changed the performance characteristics with the noise cancel routine, that would be a pretty poor design implementation. I have manually adjusted the noise cancel setting on the 800 and really haven't noticed any difference in the way the machine performs other than the obvious impact on noise stability. Yeah, it's best to not overthink it and just go detecting.

 

[cudamark]

It just seems to me that a "slight" change in the transmit frequency (say less than a Mhz) wouldn't get the job done, EMIwise, and several Mhz might be significant in performance....although the shift from 5Mhz to 4Mhz seems to have quite a bit of difference in both EMI and depth, at least enough for Minelab to have added it to the machine.

 

[vferrari]

It just seems to me that a "slight" change in the transmit frequency (say less than a Mhz) wouldn't get the job done, EMIwise, and several Mhz might be significant in performance....although the shift from 5Mhz to 4Mhz seems to have quite a bit of difference in both EMI and depth, at least enough for Minelab to have added it to the machine.

OK, but I'm not losing sleep over it. Sometimes you just gotta trust what they are saying right in the manual that they slightly shift the frequency to make it work, and trust that they've been around the block a few times when it comes to designing detectors such that they don't stupidly implement a noise cancel scheme that adversely affects performance. They are somewhat limited in what they can do because of the "do no harm" constraint and as a result, you can often see that the noise cancel feature is not always effective.

 

[midalake]

With myself being at a noisy EMI beach, for parts of it. I usually reset noise cancel LOTS. I wish there was a rime or reason to it Seems like the same or different numbers with the same problems. Seldom does it relieve ANYTHING!!

 

[vferrari]

With myself being at a noisy EMI beach, for parts of it. I usually reset noise cancel LOTS. I wish there was a rime or reason to it Seems like the same or different numbers with the same problems. Seldom does it relieve ANYTHING!!

Dave, since the noise cancel routine appears to be designed to adjust the “front end” transmit frequencies and target receive filters (typically wide field steady power line/power transformer/radio tower type noise) it is only really addressing EMI that is primarily coming in via the coil and has little effect on the EMI that is penetrating the control box that is emanating from transient near field sources such as cell phones and wi-fi.

 

[cudamark]

That's for sure.....WiFi seems to be my main problem that noise cancel has a problem with. Nearby detectors are absolutely no problem, and power lines haven't been much of a problem either. Radio transmissions are sometimes a problem, especially near military bases. They must have some powerful transmitters or a particular frequency that affects the detector to a greater degree. I guess I'll have to do some testing on the Noise cancel manual settings to see if I can detect any differences running it from -9 to +9.