A few really deep rings I got with the CTX 3030 big coil a few years back by way of signal balancing–some close to 20″.
My CTX had been in the shop for quite a while–it had the old config and leaked more than once. One bulkhead, one set of clips and two lithium cells later she was still drinking brine. Thanks to Minelab I’ve just gotten a like new machine and am very excited and grateful. (…the metal detecting equivalent of a virgin in the afterlife). Anyhow, I do a lot of testing in my basement in that the interference from furnace, household panel and dryer simulate actual tough salt surf conditions. If you can tune a detector inside–you are doing something right. This is especially true of big coils. I have the large coils for my CTX, Equinox 800 and a WOT hardwired for my Blue Tubes Excal. There is a ton to be learned about signal balancing big coils under these high interference conditions. This kind of testing has gotten me a lot of deep, heavy gold in conditions where there is a lot of pro-level competition. First, its amazing how much of a difference in performance loss (even in air) there is between large and stock coils. These big coils just suck the interference out of the air (or water). What I notice is that target sounds have a much more “inverse” .sound–as if the threshold was “taking over.” The higher you turn the Gain–the quieter targets get. In some instances–the stock coil actually hits targets further out. (Talk about a “teachable moment!)”
One thing that’s worked well with the CTX has been to run a P2 version of one of the programs that features one or a couple of reject lines. (Andy’s Beach for example) This seems to balance the signal and reduce all the reverberation-type noise. This works well in the field too–especially of you don’t pile on more interference from current and any incline. This involves a slow sweep speed and working only North / South. I’ve gotten some rings down at the 20″ level this way. The Excalibur–as hard to tune with the WOT coil as it can be–is a simpler platform with less going on–electronically. While it can’t be run that high–maybe at 1 to 2 o’clock is a balanced signal–it does get great depth in discriminate–taking rings at an easy 18″-plus. It’s also stable.
Now the Equinox is one of the hardest detectors to tune with a big coil that I’ve used. My usual 2 Tone method works–but is unstable and gets only moderate depth. My super-sharp responding gold magnet “Undertune” (GB -9 / tone “25”) method is out of the question. Without Ground Balancing–the threshold is lilting, uneven and requires careful coil control. I’ve seen videos of guys running down at “14” Gain–unacceptable. Why bother with a big coil to run that weak of a signal? The sense I have is that this detector has a hard time supporting a coil that size. When I run near-preset B2 with 5 Tones–it seems more balanced and stable. This is about the only time I’ve ever been driven back to the pre-sets to balance a detector. It’s a good coil–but hard to balance–just saying. I see a detection signal as being kind of like an arithmetic sum. When you keep subtracting with say, fast water, Gain too high, (in this case) Recovery Speed too fast, high saline conditions bottom contours / inclines and the work a detector does with a highly processed signal like that of the CTX or EQ–what’s left is not always enough to get any more depth than the stock coil. The larger the coil–the greater the affect these factors have. I’m still learning with both of these detectors / coils but am really struggling to get any respectable depth–especially with the EQ. I’ve a lot of great signal balancing “tricks” up my sleeve–including smoothing out the threshold with a “1” discriminate setting or even bringing up the Tone Break–but have yet to find anything that convinces me that a narrower–more manageable detection field drawing less interference would not perform better. I’ve also been instructed on the forums to keep the Recovery Speed low–down at “4” with the big EQ coil. This is just not that stable in salt conditions unless its absolutely still. Of the two, the CTX wins in terms of stability–but for coils that size–even compared to the WOT–the depth just does not seem to be enough to justify the extra swinging effort–at least not in salt water. I’m open to Equinox big coil salt water suggestions. Otherwise–next trip–the coil at least–is staying home.
cjc
From the “War Room”.