Minelab noise cancel

[Danno]

Does anybody know what this actually does, does it simply shift all the frequencies similar to manually shifting them for EMI etc.

The original Explorers seemed more sensitive on certain channels.

[Skippy]

Yes, it just shifts both frequencies up and down, by about 10% each way, maintaining the 8 : 1 ratio always.
This tired old thread on Dankowski's forum has the details in it.
http://www.dankowskidetectors.com/di...2,24272,page=1

[Carl-NC]

Thanks for posting that link. I remember the discussion, had no idea where to find it.

[bklein]

I don't think the Equinox does noise cancel like the CTX does.
I seem to remember seeing the CTX frequencies shift but not with the Equinox.
Weird too that the NC number on the Equinox rarely repeats on retries.

[Carl-NC]

I don't think the Equinox does noise cancel like the CTX does.

It does, I looked at it.

[Danno]

Thanks for replies, very helpful

[bklein]

Have to disagree with you Carl.
I have a simple coil that is feeding into my spectrum analyzer. The CTX transmits through the noise cancel procedure - the Equinox does not - goes completely dead.
http://youtu.be/jMr6y5hlx-A CTX
http://youtu.be/fTZQFMhwFHI EQ800
What did you see??

[Skippy]

So presumably it could generate the TX waveform 'internally', and perform the synchronous demodulation at the 3 / 4 frequencies, so it could measure the resulting noise. And then it steps through all the frequency shifts, chooses the quietest ( this could be an 'intelligent' decision ) , then turns on the coil TX drive and starts operating normally.

[Carl-NC]

The CTX transmits through the noise cancel procedure - the Equinox does not - goes completely dead.

Yes, that is correct, the Equinox goes through the process with the TX off. I thought you were saying that the Equinox doesn't shift frequencies.

[bklein]

Why does it need to generate a TX for nc anyway? It is running like a ham radio guy looking for an open frequency to work in. Find a clear freq band and send CQ. :-)
Why is there so much variability in the equinox nc number? It really jumps around if you try multiple runs. Looks to me that they should just leave it at zero unless there is a significantly repeating signal it picks up. It does sort of stabilize if you bring the CTX nearby. The CTX is more repeatable.
It would be interesting to have it run in an EMI detect mode where it would display RX signal as you move the coil around...
Wonder why the equinox cannot just take care of nc on its own - a real auto nc.
When I do notice a nearby EMI disturbance with the Equinox the nc rarely makes a big difference to it for me. Might depend if there is a movement sensor inside like on the CTX as to whether they can do it automatically I guess.

[Carl-NC]

It really shouldn't make much difference whether the TX is running or not, except for the "idiot factor" where the user has the coil close to a target. If the coil is in the air, the RX sees very little TX and it is synchronous besides.

Here's a guess: By turning off the TX what they may be doing is cranking up the preamp gain to get better sensitivity to EMI. I sorta doubt it as the preamp is in the coil and that would make for a more complex circuit where you don't want a complex circuit.

Another guess: If there is little EMI to deal with, then that might explain why it is inconsistent.

A real auto-NC (done as you hunt) probably requires TX dead time as with a PI.

[Skippy]

I doubt they're increasing the pre-amp gain, but they may be running an effective higher gain in the post-processing, perhaps by averaging multiple samples over a longer period of time than would normally be done in general use mode.
What 'noise cancel channel' the machine settles on may depend on what mode it's in, too. So the 'gold 2' mode may put more emphasis on the 18.2 & 39 kHz being clear, for example.