jas --
Yes, on the iron bias. If you are trying to "unmask" coins that are "hidden" by the presence of nearby iron, a lower iron bias is what you want. That's the short answer. LOL! Here's the long one...
Let's define, for the purposes of discussion, ANY situation in the ground where you are getting a mix of low tones and high tones as a "mixed target."
Obviously, one type of "mixed target" arises from a coin lying in close proximity to a nail. However, SOME "mixed targets" occur simply because you have a nail (low tone) that is giving you some high-tone "falsing." In other words, not "two separate targets in the ground," but instead ONE target (the nail) that "confuses" the machine a bit, presenting some high-conductive traits within the "receive signal" being seen by the coil, along with the more dominant, low-conductive iron response. (Obviously the degree of this falsing depends upon sensitivity or "sparkiness" of the machine, the frequency being utilized, etc.)
In a PERFECT world, we'd like to have a super-sensitive machine, yet one that does NOT "false" on nails, but instead correctly IDs them ENTIRELY as iron -- and only gives us the "high-tone/low-tone mix" when there are actually two co-located targets. But, we don't have that ability yet. SO, this is where "iron bias" enters the picture, being a tool that can "help" a bit.
If all we want to do is "eliminate falses," we can run iron bias up high, and what we are telling the machine is "on mixed targets, instead of letting me hear iron tones AND occasional high tones, eliminate the high tones...i.e. 'bias' the response toward all iron tones/IDs." This can be good, in that you won't be bogged down by the "sparkiness" of the machine, and you can focus only on the clear, solid, repeatable high-toning targets -- while ignoring most of the nails (as those nails will now ID more solidly as low-tone iron). HOWEVER, the obvious downside is, you will miss some partially masked coins -- because, again, you have told the machine (with your iron bias setting) to "de-emphasize" any high-conductive response that is occurring near primarily iron targets.
ON THE OTHER HAND, if we want maximum unmasking ability, we can run iron bias down low, and in that case what we are telling the machine is "anytime you are seeing some high-conductive response near an iron target, EMPHASIZE those high tones for me; allow them to bleed through." In other words, "bias" the machine toward an emphasis on high tones, in any "mixed target" scenario. The benefit of setting up the machine this way is, obviously, if your "mixed target" happens to be a coin next to a nail, you will be allowing the "coin response" part of the signal to be emphasized -- and thus making it more likely you HEAR that co-located coin. Therefore, low iron bias settings allow you a much better chance of digging "partially masked" coins. HOWEVER, the obvious downside is, you will dig more nails, as again -- high-tone "nail falses" are also a "mixed target," and your low iron bias setting is, again, telling the machine "emphasize" THOSE high tones, also, just the same as it would any high tones associated with a partially masked coin.
SO -- obviously, it's a trade-off. And the answer of "where to set the bias" depends upon what you are trying to do, what your goal is at that time. Do you want to hunt "quiet," and dig ONLY the solid coin hits? OR, are you hoping maximize your unmasking capability in a heavily hunted, nail-infested site?
After all that long-winded response, the point is -- in your speicif case that you described, running iron bias LOW gives you the best chance of digging any partially masked coins in your very trashy site, but it will come with the downside that you will likely dig more "falsy nails." I think you are seeing this, based on your post.
As for your recovery speed, I'd run it high, at this trashy site, since you are trying to "unmask." BUT, again -- as you note -- there is a trade-off there, as well. High recovery speed means less depth, in general, while lower recovery speed allows greater depth (at slower sweep speeds). NO, you will not get "max depth" if you run recovery speed high. BUT, similar to running iron bias low, a high recovery speed will maximize your machines ability to "see" a coin located very close to a nail. Basically, you can think of the analogy of "snapshots..." If I imagine recovery speed from the analogy of telling the machine to take more "snapshots" in a short period of time, and if I shorten my audio/tone response so that I can HEAR each one of these more rapid snapshots, then I have a better chance of hearing multiple, closely adjacent targets, instead of letting one target's audio response potentially "bleed over" and "stifle" the response of the nearby target (as would tend to happen with slower recovery speed and the associated "longer" tone responses).
You are worried about depth loss, with high recovery speed -- BUT -- at a really trashy site, it's hard to get max depth ANYWAY, due to the density of targets. If you have reason to believe there are deep coins there AS WELL AS shallower coins that are masked by trash, then you might need to hunt the site multiple times, at different recovery speeds and sweep speeds, in order to recover as many of the targets as possible. With that said, eight inches of depth, at high recovery speed, is really pretty good, from my view. In other words, not a HORRIBLE loss of depth, but with the benefit of much better unmasking capability. One thing you might do, is do some testing on coins you have buried at various depths; run them at high recovery speed and faster sweep speed, and see how deep you can detect the coin...and then, lower your bias and re-run the coins, at a much slower sweep speed. You will then be able to get a rough idea of the effects of fast recovery, high sweep speed, vs. slow recovery, slow sweep speed. Knowing these "bounds" on either end of the machine's capability, will help you to make a more "educated" decision on how you want to run your machine that day, based on your goals, the type of site, the amount of trash present, etc.
Finally, you asked about sweep speed. That's a tough one, and I'm still trying to work that one out -- testing to see how to match sweep speed to recovery speed.
Here's what I can say. If you run your recovery really low, like minimum, you need to sweep REAALLLY slow, to get max depth. If you run your recovery high, you need to run FAST sweep speeds, to get maximum depth. BUT -- what I haven't yet figured out is, if I am running fast recovery speed, and I am NOT concerned with maximizing depth, but instead focusing on maximizing unmasking capability in dense trash, is it best to sweep SLOW, so as to give the machine the BEST chance to hear all targets that are in close proximity to each other? YES, a faster sweep speed will yield maximum depth when running high recovery speed...BUT...my "inkling" is that the slow sweep speed combined with high recovery WILL give maximum SEPARATION ability. I still need to test this, though, to be sure. It seems obvious that slower sweep speed should maximize separation ability using high recovery speed, BUT -- I want to make sure that slow sweeping does not in some way harm the ability of the machine to "do its thing" (accurately, effectively report on all targets) when running high recovery.
Again, what I feel fairly certain of is slow sweep speed with low recovery speed maximizes depth (and is in fact the DEEPEST way to run the Equinox), while high sweep speed with high recovery speed also maximizes depth for that recovery speed (though, not as deep as slow recovery, slow sweep speed). BUT -- I still need to verify my sense that SLOW sweep speed with HIGH recovery speed might maximize unmasking ability of the unit (while sacrificing some depth). This is how it SEEMS so far, but I need more testing with higher sweep speeds and co-located targets, to verify this to myself...
I know this is "long winded." But I hope it helps a bit...
Steve
