Rodt said:
Mate a new owner and learner here. Three questions from the above
1. What do you call "pretty high" THS A? and
2. Logic would tell me that you need to focus on smaller targets as most of the larger would be gone by now but does this mean it won't pick them up if you happen to stumble across? I suppose it would be handy to know how you define smaller and larger.
3. Unless I have misunderstood how do you setup differently for small and large targets?
Thanks in advance
Rod
hi Rod,
This stuff isn't really critical to operating the QED but I'll try to answer your questions.
1. For the purposes of accurately finding THS-B's null, "pretty high" means, well, it depends. When you raise THS-A, the range of THS-B values that are not noisy shrink.
With a low THS-A (say, 30), you may a range of THS-B values that are silent, maybe its from 45 to 55. So it may not be clear which one is the null/neutral THS-B value.
You could just leave THS-A at factory default (IIRC that's 30), and then follow the manual to find B's null. You're directed to reduce B until it starts to get noisy, take note of its value, then increase it til it gets equally noisy, and halfway between those is the null value. What I described is a perhaps more straightforward and sure way to get your THS-B null. Might also be in the manual somewhere, don't remember.
Raise THS-A a bit, say to 50, and the range of silent THS-B values shrink down to say 48 to 52. If you raise THS-A higher, maybe to 75 or 80, you'll find that there is a single THS-B value that is the quietest. That's your null. Can't give you a specific THS-A value - this is just a generalized process to find your THS-B null.
2. Your logic is sound, an indeed there are far, far more small targets than large. This would have been the case before the big ones had been found as well. By "setting up for small targets", we mean that the detector will be set up to get the best depth on small targets, but you will sacrifice depth on large targets by doing this (and vice-versa).
Small targets are those that produce a rising pitch response. Large targets are those that produce a falling pitch response. You could say that small targets are under ~2.5g and large are over that, but it really depends on the shape, size, and texture of the target. The detector is not responding to the mass of the target, it's responding to its electromagnetic characteristics.
More specifically, for the QED, my understanding is that targets are divided into rising or falling pitch responses according to your ground balance value. The manual has some information on the "GB hole", which is a particular target response that matches closely the signal the ground is giving off. Targets with this response will be totally missed by the detector. This is pretty rare, though. The GB hole target response is in between rising pitch and falling pitch target responses. Changing the GB value shifts the GB hole target response, and changes which targets are rising or falling. You need not worry much about this.
So the question is, do you want increase your ability to hit gold that is far more common (small), but lower your chances of hitting a larger target? Or, do you want to increase your ability to hit larger targets but skip some of the more common small gold?
The Minelab detectors have an advantage here in that they way they send out pulses focuses on both large and small targets. It's not apples to apples but you could imagine that they have both a high and low THS-B value at the same time. This is perhaps the most significant difference between a GPX and a QED.
3. You set up for small targets by reducing your THS-B, and for large targets by raising your THS-B. You can also leave THS-B at its null value and then can increase THS-A higher. My understanding is that you'll get a *decent* response on all targets, but really can only get max performance by moving THS-B up or down from null, and lower THS-A a bit to accommodate the more extreme THS-B values.
