"Chance favors only the prepared mind." - Louis Pasteur
You can increase your chance of finding more targets by performing a few nuisance chores on your VLF detector before going into the field (and a few more when you get there). None of the following tasks are critical.
In fact, you may be perfectly satisfied with your machines operation if you dont do them. But, collectively, the potential problems they correct can otherwise mask signals, cause you to overlook returns, or prevent you from receiving some responses from good things under the soil. Theyre worth a try.
Clean the search coil with a damp cloth. If theres a protective coil cover (skid plate), remove it, even if it fits snugly. Clean the inside of the cover; clean the coil; then reinstall the cover. Small metallic particles and salts that have accumulated on your search coil from past explorations can work their way into tight spaces.
Although they wont normally give you false returns, they can increase the background noise, and sometimes shield transmitted signals and target returns, thereby reducing their levels. They can also change the phase relationship of the transmitted-to-received signals slightly, which would have an impact on discrimination.
Theres no need to clean the search coil thoroughly each time you use the machine, but a periodic cleaning will improve its performance. Loosen the wing nut or knob that locks the search coils angle, and clean the threads and surrounding area.
Partly tighten the wing nut or knob enough so the coil remains in position, but can be moved readily. Then, adjust the coils angle so its parallel to the ground when you hold the detector in your normal scanning position. With the coil at that angle, tighten the wing nut, or knob, finger-tight. Verify that the coil remains parallel to the ground, and does not change position if you move or lightly shake the detector.
Although you might not notice small changes in the coils attitude while you work in the field, signals in both directions can be attenuated enough for you to miss weak returns from deep or small targets. This task neednt be done each time you use the detector either, but always verify the coils angle is correct. If the angle doesnt remain stable, you can install an inexpensive stabilizer available from detector distributors.
Check that the connector on the search coil cable is mated snugly with the one on the control housing. If not, unscrew it, clean out the threads on both connectors with a cotton swab or lint-free cloth, and check that theres no residue in the threads. Then reconnect the two sections. Make sure the connector sleeve screws on smoothly and there is no cross threading. Snug the connector finger-tight.
Most detectors allow you to tune out returns from minerals and mineral salts in the soil, via a ground balancing operation. This may be a manual or an automatic procedure. If your detector has a manual Ground Balance adjustment, perform the balancing routine given in your operators instruction book.
Of course, you wont be able to do this on a machine that has automatic tracking ground balance. And some manual ground balance machines have an indicator marking that you can align with the cursor on the adjustment knob. This gives you moderately good results without all the fooling around.
But, except for automatic track balance on the most sophisticated microprocessor-controlled detectors, both automatic balance and one size fits all manual settings are trade-offs. They provide convenience in exchange for a loss in optimum performance. Most detectorists wont notice the difference during ordinary coinshooting, although depth readings and pinpointing will be more accurate with proper balancing. But the recommended manual procedure might just get you a few more good finds. Some metal detectors are silent search machines, while others have an audible threshold that can be set by the user.
The audible threshold machines greatest sensitivity is at the minimum discernible point, where you adjust the threshold level until you can just barely hear the hum. Doing so will pay off with more detected targets.
Phones are preferable to speakers, because they bring the signals right up to your ears, block external noises, and keep your ears warm on chilly days. Headphones that have a volume control on each earpiece are the best. One benefit is that you can tailor the sound level for each ear. Another is that you can set the volume to maximum on a detector that has a rotary or digital volume control, then adjust the controls on the phones for comfort. That way you receive everything that comes out of the detector, to be evaluated at whatever level you prefer. With detectors that do not have volume controls, such phones are not just desirable; theyre mandatory.
When scanning, you might want to remember that the outer loop(s) on the popular concentrically-wound search coils transmit the signal, and the smaller-diameter inner loop receives target returns. This consideration might suggest overlapping your scans more closely and pinpointing targets with greater precision. If you dont care to do all of these chores, at least do some of them. Anything that gives you an advantage in the field is beneficial. It pays to be prepared.
Authors Personal Experience
Bansky, Alan, Short Range Wireless Communi-cation (2nd Edition), Elsevier Pub., Burlington MA, 2004
Hickman, Ian, Practical RF Handbook (Fourth Edition), Elsevier (Newnes) Pub., Burlington, MA, 2007
U.S. Dept. of Defense,MIL-HDBK-419 Electro-magnetic Compatibility and Grounding, continually updated.
Very nice dime found in small "hunted out" patch after the chores recommended here were performed.
Except in heavily mineralized soil, this quick ground-balance setting (red line) works. But the full manual ground balance procedure produces more reliable indications.