Thread: Best Detecting Frequencies
07-08-2011, 10:49 PM #1
Best Detecting Frequencies
So what is the best overall frequency for limiting emi and getting good depth when metal detecting. I hear V3I folks including myself talk about EMI, and I hear the MXT or M6 or even DFX talk about great depth and no significant EMI issues. I hunted next to a DFX and I had EMI issues and even after making the standard and extended adjustments could just barely hunt. THe DFX was just working away no problems. Just looking for more detailed info and explanation.
07-09-2011, 05:45 AM #2
what coil was you using if it was the 10DD they are bad for it and some time the detector will talk to each other with the MXT we can't get within 15 feet of a M6 if you were hunting side by side it could have been cross talking good luck and good huntinglive it, love it, thank it, dig it, low and slow is the way to go
07-09-2011, 06:12 AM #3
Not to split hairs, but there's really two things you need to worry about. EMI and Crosstalk. EMI = Electromagnetic Interference - is the electronic "noise" that you get from power lines, electrical equipment, etc. It is "generally" a harmonic (multiple) of 60 Hz.
Crosstalk is the reception of one detector's signal by another detector working on the same or very similar frequency, such as an MXT and an M6, or an MXT and a DFX. All three of these units share the 15Khz frequency.
V3i's 2.5Khz is a "close" frequency with DFX's 3.0Khz.
Now - to further exacerbate the issue, there is "hetrodyning" or "mixing" of signals in the coils. A 2-freq unit will have 4 "primary" freqs in the coil - the two original frequencies, the sum of the two frequencies and the difference between the two frequencies. In the case of DFX, you'll have 3Khz, 15Khz, 18Khz and 12Khz all running around. Then, these can mix, etc, etc, etc.
Note: This is how "some" units claim to have XXX frequencies active, even though they aren't using them.
At the end of the day, the lower freqs, 2.5Khz / 3.0Khz are generally the worst for 60Hz based EMI. Switching to 22.5Khz / 15Khz is an "accepted treatment of choice" along with frequency offset and dropping sensitivity. Changing coils also helps.
The only way to effectively deal with crosstalk is to (1) use freq offset and (2) move away from the other detector.
Hope this is helpful.If there's anything I hate worse than diggin' pulltabs, its missin' a gold ring.
07-09-2011, 11:41 PM #4
That does help Fox. We were hunting far apart, so I was not getting any cross talk. The hetrodyning of the signals blows my mind. Must be a good phase shift processor in the box. Hey, as the signals are mixing away, what weight does the processor give the mixing and not primary frequencies?
07-10-2011, 06:48 AM #5
The processor doesn't have to worry about such things. Think about your radio / TV / etc. ALL the frequencies are in the air. Its what the receiver is tuned to "see" that matters .... The range of signals that the receiver can pick up is called "bandwidth". While its not quite as simple as it sounds, look at DFX as a radio with a receiver with a bandwidth of just below 3Khz to just above 15Khz. VX3 / V3i would have a front end that passes frequencies within a bandwidth of just below 2.5Khz to just above 22.5Khz. Techlology allows for the supression of unwanted frequencies that helps quiet things down, analog and digital filtering techniques add to that process, etc, etc. When you use Frequency Offset, you're just kinda "retuning the radio to a station with less noise".
The above is an "example of how things work" to help understanding. How its "really done in detail" is proprietary to White's design.
Hope this is helpful ....If there's anything I hate worse than diggin' pulltabs, its missin' a gold ring.
07-10-2011, 11:01 AM #6
Thats way I turn off my detectors,when I see other M.Ders,coming up to talk to me on a hunt
They might be trying to throw my detector off, so I find less"Learning is the eye of the mind."
Thomas drake 1633
07-10-2011, 09:45 PM #7