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CTX noise cancel channel frequencies.

I

INSAYN

New member
I've been toying with my noise cancel channels manually up or down when I get a solid repeatable deeper signal try to see if one hits better than the other.
Although I haven't really got a solid baseline yet on which channel is better for lower conductive, vs higher conductive targets I do have an idea where they should be.
I just can't find any info anywhere on what channel is the highest frequency, and which is the lower frequency?
 
Lowest freq will be 1 and highest will be 11 but I see not much difference than whatever channel you use .,Letting the ctx decide is your best bet because it knows what to use when it sample's the ground . sube
 
I'm pretty sure Sube is correct on 1 being the lowest, but the difference between 1 and 11 is minimal, it is just minor frequency shifting like other detectors with frequency shift. Some people claim they get deeper with one channel over the others, but the channel with the least interference really gets the deepest IMHO.
 
Like I said, I haven't really established any tell tell signs of whether one does any better than the other or not.

Thanks Sube and Larry.
 
Like you INSAYN, I've been experimenting with it too and find little difference in them. Some posted awhile back about it helping them get depth but I don't know the magic of it.
 
3.125kHz and 25kHz are the two frequencies sampled by the CTX (and E-Trac)

Channel 6 is standard freqs (above).

The detector can adjust from the above frequencies by 10%.Thus, the high freq of 25 kHz would be pushed to 27.89 kHz if Channel 11 were used, or dropped to 22.2 kHz if Channel 1 were used. Similar percentage change for the low freq.

The difference between 22.2 and 27.89 kHz is minor and isn't likely to change the detectability of targets, but some think higher channel selection if better for illuminating low conductors. Perhaps, but not if you've inadvertently allowed EMI because the auto setting was ignored.

Johnnyanglo
 
I don't know what the exact parameters are for each channel. And frankly, I believe there are too many variables (soil conditions, technique, site, functionality settings, Sensitivity settings, interference harmonics, etc) to make a definitive statement as to which channel might "work best" for specific targets. One person posted here a few weeks back that he thought the shift was 10%. I can't imagine it being that much.

The interference we might encounter is in the form of harmonic waves, created by electrical transmission lines, electrical devices, appliances, communication towers, other detectors etc. The Noise Cancel function allows us to shift the band of transmitted frequencies (fundamental frequency plus direct harmonics) to a slightly higher or lower band of frequencies, in an effort to reduce the effects of the interference.


My thoughts.......When I did a factory Reset of my CTX, the Noise Cancel channel was reset to 6. With eleven total noise cancel channels available on the CTX3030, this would suggest (to me) that adjusting the NC channel to channels 1, 2, 3, 4 or 5 will offset the transmitted band of frequencies to a slightly lower frequency wave range. And adjusting the NC channel to 7, 8, 9, 10 or 11 will offset the band of frequencies to a slightly higher frequency wave range. How much does each channel offset the frequencies? I don't know. But I would suggest it is very slight........and in my opinion, likely less than half a kHz. With the limited Noise channel documentation available for the FBS detectors, I can only reference how the Noise Cancel channels are established in the X-TERRA. (their other model with smart coil technology) With the X-TERRA, the resonant frequency is obtained with Noise Cancel Channel 0. From there you can either shift to a negative NC number or a positive NC number. Each step in the NC channel progression only shifts the operating frequency by .035khz to .08kHz, depending on the frequency of coil in use at the time.


BarnacleBill made an excellent post a few years back, regarding the multiple frequency of FBS detectors and how one must be careful when analyzing them with a Frequency Counter or Scope. In part he said: "By varying the length of the pulses and spacings you can create a wide variety of frequencies. Measuring the FBS transmit output on a bench doesn't really give the whole picture, because once the detector begins to measure the ground it can vary the transmit waveform."
I would encourage anyone interested in learning more about the transmitted frequencies and how they are received, take a look at his post. Here is the link.....
http://www.findmall.com/read.php?86,1701315,1701315#msg-1701315


HH Randy
 
So as the frequency gets higher the difference becomes less important?

I ask because I've seen the difference between say 10 KHZ detector and a 15 KHZ detector, about the same you suggest is not enough to make a difference, on small gold?
 
If the high frequency is indeed 25 KHz as some claim, it is a weak harmonic of the primary low frequency and I don't really know the purpose, but it certainly is not used as a hunting frequency or small gold would really shout out at you........:shrug:
 
]"it is a weak harmonic of the primary low frequency"[/quote said:
Yep. It is used, but apparently (no hard evidence) the primary frequency is where the energy is at as compared to the harmonic. The main purpose is to compare the time constant of the target between low and high frequencies for the purpose of discriminating ferrous/non-ferrous. A single freq detector at 25 kHz puts all its energy into the xmit freq - better for low conductors, like natural gold and thin jewelry.

Johnnyanglo
Click to expand...
 
Unfortunately, all this is speculation and mostly deals with what a detector transmits which is far less relevant than what a detector processes. We really have little to no idea what/how the E-Trac/CTX processes incoming information which is what really matters. Personally I would think there would be quite a difference between a 10 KHZ and a 15KHZ detector IF that signal is processed. Even if the transmitted signal is weak how do we know that area of the processes signal isn't boosted? Other than that obvious lack of low conductive sensitivity.

I guess rather than the typical long winded post based on speculation I should just shoot a video of a deep target at different noise cancel settings. The proof is in the pudding so they say LOL.
 
Good info but some is beyond me, I wish there was a good book that explains better how the FBS & FBS II really works. Probably would help if I read the Etrac/Explorer book that's out but sure would be nice if a good book was out for the ctx!
 
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