Iron and Reject Targets (Cross-Feeds)
This is an interesting and telling performance characteristic of the CTX. It's as if the two target ID “metrics” (Conductive and Ferrous) “clash” where there is a strong input from both--producing a tone. Initially this will sound like a good signal--especially when you are running Manual Sensitivity. As you make to repeated coil passes the response will weaken or drop out altogether. This is a “cross-feed.” A cross feed is a cumulative or “summated” response that (just as with any high Gain VLF) is an audio representation of something the detector can't initially classify.
It's a “half-breed”--part iron, part nonferrous. In effect the detector is channelling the ground's signal up though this hard-to-classify object. These objects will be “attached” (electronically speaking) to the ground by their rusted or corroded content. As with any VLF machine these will be reduced in strength with lowered Sensitivity settings or by changing to Automatic Sensitivity. While I've never been a big fan of the reduced depth and “shuttered” audio effect of Auto Sens--situations where you have multiple tones continually coming in from rusted caps or tin are a situation where this setting can be an effective solution. While in many of these instances I do mention Auto Sens as a viable solution, keep in mind that with Auto--there is always a price to be paid--a “trade-off”. Auto adds greatly to the work you are asking the CTX to perform--and there are attendant performance losses. (More on Auto Sens later).
There are often audio characteristics to these responses that make them recognisable--weak sounding, or wavering in the tone. I've also noticed that many of these falses lack the proper “waveform” of a good target--that is, they are not peaked in the middle--a flat tone with no definition. In keeping with the part-ground source of the signal--they stand out from it poorly in the audio reporting.
In-ground iron can also be seen as a source of interference. These spikes and larger iron objects will come in as full-on false signals. These can also often be recognised by features of the tone. Sometimes there will be “chirps” and “pings” accompanying the normal-sounding part of an iron false.
Recognising falses is not the intention of this section of the book. The point here is that where you have a lot of iron the CTX's complex signal has more to do. This is also something that needs to be responded to with your settings choices--(lowered Sensitivity or Volume Gain) and slowed sweep speed to allow the CTX to process what's under the coil.
From: "The CTX 3030 Gold Hunter's Guide"
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