Book Excerpt: Modulation

[cjc]

Book Excerpt:

14/ Modulation

Modulated audio acts to reduce noise and response irregularity in a high gain audio platform. That’s a lot to manage. Modulation defines each tone and makes all signals sound better and more the same. This also represents an artificial, distorting influence--a kind of audio “no-man’s-land”where small objects sound bigger and large targets are “clipped down.” This is especially true in the “tone ID” modes.

For the operator, modulation makes it harder to tell a deep faint response from a small surface one. In conjunction with Gain, modulation makes small responses more distracting--sounding fuller and more solid. Modulation also makes tiny mineral, seabed or black sand variations jump way up to sound more like good signals. Determining a response’s shape and distance from the coil are also harder. What you have is a digital representation of ground and targets--more of a measure of the relative differences between the two than an actual metal object reading.

Another consequence of this is that big targets sound smaller--cans--sunglasses--all are modulated to often sound like they are (more) coin or jewelry-sized. I’ve had some particularly frustrating deep-water hunts with the Equinox giving tantalizing small indications on what turned out to be super-deep “rotten glasses.”

This operating characteristic can be confusing for new hunters. This, in particular is an Equinox operating characteristic that is easier to make sense of and manage with some solid, basic instruction. For anyone--the “trade-offs” that derive from the Equinox’s heavily modulated signal are its most frustrating feature.

1/ The first, most basic method of managing a heavily modulated signal is to turn the volume down. Even going to “24” or “23” makes a huge difference. This makes for more audio distinction between weak and strong signals. Many CTX hunters discovered this after becoming frustrated with that detector’s tendency to bring up tiny conductors. With its high frequency weighting on several of the pre-set modes this is more so of the Equinox. While many of the underwater headphones that are available are quiet to begin with and don’t allow much of a margin for reduced volume--the stock 800 series wireless set do.

2/ Focus upon the more solid signals. This is a critical Equinox skill in any context. Even as a pulse hunter who has experience with fast Delay machines that hit running shoe eyelets loud and clear--the Equinox was initially exasperating to use for me because of these modulation-boosted targets. While I see some patient hunters getting good results “micro gold” hunting this is at highly specific types of locations.

The solution is simple basics. Rather than digging endless tiny part-responses--use Pinpoint to check for solidity--and do a quick angled pass to see the consistency. (See “Pinpoint” below). With practice these small conductors will become more obvious in Discriminate as well.

This is the way to offset the distortion of a modulated signal--but still get its benefits. This is where the above mentioned “correlation” comes in--looking for “sets” of target characteristics to double check what the audio is telling you. Even when examining tiny “earring-sized” sounds it’s possible to screen for solid targets and use this as a basis for gathering a full target profile. Each signal feature (size, strength, solidity, position in strata…) should confirm the others. The depth meter is also a good tool for offsetting the distortion of modulated audio. Signal depth and signal strength should be “in keeping.” (More on this type of method below). Modulation is more active in the Tone (break) ID modes (especially “5 Tone)” so using the more fluid “50 Tone” or just “Pinpoint” are good ways to compensate. One reason that many hunters have trouble adjusting to the Equinox is that again, this high Gain / high frequency / modulation combination reduces your ability to judge how far from the coil something is. This in turn throws off your sizing.

The number of hunters I see on “YouTube” videos trying to ignore these simple target testing basics is laughable--with many trying to pass off this as some cool “dig everything” ethos. Again--not “everything” is “anything” and a machine like the Equinox will tell you when not to dig sometimes--loud and clear.

From "Skill Building with the Minelab Equinox Series Metal Detectors" by Clive James Clynick (2019)

[FloridaSon]

Makes sense, just ordered.

[FloridaSon]

Could you explain exactly how to "use Pinpoint to check for solidity"? From the above excerpt? Thanks

 

[Chase Goldman]

13 hours ago, FloridaSon said:

Could you explain exactly how to "use Pinpoint to check for solidity"? From the above excerpt? Thanks

 

How many times have you swung the Equinox over a sweet sounding quarter coin tone only to discover it was an aluminum can?  There are some tonal nuances a trained ear can tell the difference side-by-side in the ground, but it is even hard for a trained ear to tell the difference on widely scattered targets in a field or on the beach.  And you certainly can’t get a good handle on the target footprint with the processed search mode tones.  
 

Pinpoint mode to the rescue.
 

Since pinpoint is a non-motion mode (vs. normal detect mode which requires you to keep the coil in motion over the target to register a target tone), you can use it to quickly ascertain the relative size of shallower high visual or tone ID targets to give you an idea whether you are swinging over a coin sized object or potential junk with a much larger footprint such as a beer can or large falsing iron target (e,g., horseshoe.).  This is accomplished by tracing over the target with pinpoint engaged.  The larger objects will invoke the high pinpoint tone over a much larger footprint area than a smaller coin, ring, or button-sized target as the pinpoint tone rapidly drops off as the coil center crosses off the edge of the target footprint.  This method becomes less effective for significantly deeper junk targets as the relative pinpoint signal strength "footprint" shrinks even with larger targets as their depth increases (you can simulate this by lifting the coil off the ground while tracing something like a beer can).

You will probably dig the target anyway just to be sure, but at least this way your expectations are properly set such that you will be pleasantly surprised if it turns out to be a keeper rather than the other way around.

I personally use pinpoint more for target tracing, when I am in doubt about the true nature of a good sounding target, rather than going to pinpoint mode for pinpointing, because I can pinpoint pretty effectively by wiggling off high probability coin-sized targets.

[FloridaSon]

Perfect. That is a good clear explanation That I can use. Thanks 

[Joe D.]

Chase,

I am also new enough with the 800 to always second guess my target identity! But that is how i dug a 1911 gold pocket watch a few months ago! I really don't mind digging most everything! I feel it's the only way to learn a detectors language! Even then, i refuse to miss anything! Except maybe those damn zincons!!

Thanks for the lessons, there much appreciated!👍

[cjc]

On 11/19/2019 at 7:58 PM, FloridaSon said:

Could you explain exactly how to "use Pinpoint to check for solidity"? From the above excerpt? Thanks

 

Move the coil to one side of the target, trigger--and sweep evenly across.  Try and do this the same every time so that the ratchet does not interfere  with getting a consistent pinpoint.  The signal strength and tone will tell you how solid the target is.  If you want to repeat--begin again to prevent a detuned (getting quieter with each pass) response from throwing you off.

There's more on this in the book.

cjc

[FloridaSon]

Excellent thank you again!

[FloridaSon]

cjc and Chase;

This technique worked great on a 3 ft piece of rebar buried one foot deep at surfs edge on a saltwater beach! I dug one end to try and ID it but the length was clearly determined with the above textbook excerpt and both your explanations. 

Thanksgentleman!