Ground Balance?

[Knipper]

I've seen several posts here recently and in the past referring to pressing the "noise cancel" button as "ground balancing". Since the instructions state to hold the coil waist high while doing this, I hardly think you are ground balancing. In fact, I'm pretty sure that the Explorer series as well as the E-Trac does this automatically. Correct me if I'm wrong, but I believe the noise cancel simply selects a base frequency for the machine to operate with the least amount of electrical interference from power lines, 60 cycle interference, and other Minelab detectors, such as in a group hunt situation. This was driven home to me by a YouTube video I recently viewed from a man from England. He actually had a frequency detector that would pick up the base frequency coming from the searchcoil. It was an eye opener! He started at channel 1 (there are 11 choices in all) and went from that to channel 11. Channel one was around 16.2 Khz and channel 11 was around 12.5 Khz. Each channel changed the frequency by .3Khz to .4 Khz, give or take a point or two, reducing the base frequency from top to bottom. The changes, though small, would be enough to eliminate cross-talk between two detectors operating at close to or the same frequency; or help compensate for power lines etc. Knowing this might help in detecting certain targets that respond better to a higher or lower freqency. For example, my old Garrett Groundhog ran at 15 Khz. That was a killer for deep silver coins. My ADS III ran at 7.5 Khz, and was better at deep lower conductive targets. I'm thinking I might manually choose channel "3", as I prefer to look for older deep coins. That would be about 15khz. Now, it's winter here in Minnesota and detecting is done till spring, but I can't wait to try this! Of course, if I get some electrical interference, I'll simply change the channel and try that, but keep close to a target base frequency of around 15Khz if I can.
Any comments?

 

[IDXMonster]

Remember Terry,per the Minelab literature and NOT exactly...

The FBS machines choose 1 of 11 channels that may vary slightly in frequency to eliminate crosstalk,but transmits 28 different frequencys which are HARMONICS of the base frequency. It is NOT a single frequency machine,such as the Groundhog. Youre getting down around 1.5khz up to around 100khz harmonics, allowing it to be theoretically good at finding tiny stuff as well as deep stuff. And it is.

Kevin

 

[IDXMonster]

Also,yes....youre right about the Noise Cancel. For Ground Balance, the FBS machines put out a separate reference signal constantly to monitor ground conditions,and that signal is always adjusting to some predetermined value...

Have fun!
Kevin

 

[Chris(SoCenWI)]

Hey Terry,

How is the knife business? Finding much in MN? I'm still down in Wisconsin mostly.

The FBS detectors transmit two square waves of a fixed amplitude. Noise cancel shifts the frequency of one of the square waves by a small amount. I don't entirely understand all the math and theory but you can generate multiple frequencies from a pair of square waves. And I don't think it relies on harmonics, the amplitude of a harmonic frequency is much less than the primary one. Basically FBS uses the two waves to generate multiple receive frequencies between roughly 1khz and 100khz. Noise cancel shifts these frequencies slightly but you are still getting getting data from many different frequencies, I suspect when the machine cycles through the channels it counts noise events and selects the channel with the least events. That is why you are supposed to hold the coil still throughout the process.

As I've said a million times before, put on your head phones, hold the coil next to your head and hit noise cancel; you can hear the frequency shift as the detector steps through the frequency shifts.

Long story short I don't buy into the theory that different channels will be better for different conductors; I'm not sure his frequency counter is showing the whole picture; Charles(UpstateNY) years ago posted oscilloscope traces of the transmit frequencies. Unlike a single frequency detector you are getting multiple frequencies across 1 to 100khz, say at 1, 2, 4 ,6 10, 15, 20 etc. khz. Noise cancel may change these to 1.1, 2.2, 4.4, 6.6, etc; just a small change. It isn't like drastically doubling or halving the only frequency of a single frequency machine.

Noise cancel can make a dramatic difference when detecting around another detector, but for fairly wide band power line noise I've only found marginal differences between channels as far as allowing for higher sensitivities. And yep, it has nothing to do with ground balancing.

Chris

 

[Knipper]

Yes, I realize the multi-frequency deal with the Minelabs. Perhaps the "range" of the multi-frequencies also shift a bit when the selected one via noise cancel is chosen. I just found it interesting that whatever device this guy had, it was registering a measured value coming from the coil, and there were 11 distinct readings within the range I originally posted. After an "automatic" noise cancel, I've checked the actual value in the menu and I'd say 9 times out of 10, the value or channel chosen is 5. Maybe the differences are not enough to affect target detection, but It will be fun to try all the same. Can't hurt, as long as I'm getting a stable signal.

 

[Knipper]

Hi Chris...the knife business has kind of exploded. Fell into a new market making specialty knives for leather workers and saddle makers. Demand has been such that I only got out three times this year. But those few times were enough to make me remember how much I like metal detecting and how much I've missed it. I will definitely make time for a LOT more of it this year! The good news was, that despite getting out just a few times, I still found silver on every trip...3 mercs, a Rosie and one Walking liberty half. That's all it took to get my juices flowing again

 

[Dan-Pa.]

Well for those that feel different frequencies work better with outside interferences explain this...working around near large sign and when it got dusk Explorer went whacko when light on sign turned on...noise cancelled and ran super smooth....I am a believer...