Sunday, October 30, 2011

Metal Detecting FAQ

1. Are most metal detectors basically the same?

Metal detectors are like cars, they have many different technologies, features, and performance characteristics for their intended use. There are five basic types of metal detectors:

General Purpose-Coin/Relic/Treasure
Gold Prospecting
Underwater & Salt Beach
Cache Hunting/Deep Searching
Industrial & Security

Some metal detectors are designed specifically for one type of searching. For example, gold prospecting detectors are designed to be extremely sensitive to small pieces of gold. General Purpose models are typically not designed to detect metals as small as a grain of rice, however, offer far superior trash metal rejection compared to prospecting models.

When purchasing a metal detector, it is important to consider what type of metal detecting you will do most often, and prioritize according to your typical usage.

2. How deep do metal detectors detect metals?

The most frequently asked question and unfortunately the most difficult to answer! Most general purpose models are factory equipped to search for coin & jewelry sized metals at depths of 8 to 12+ inches depending on metal size and alloy. To significantly and consistently detect beyond 12 inches requires larger accessory search coils, and/or to give up attempts to eliminate trash metals. The 15" search coil responding to all metal alloys can detect larger metal items (coin jars) at depths up to four feet. However, sensitivity to single coins is greater with smaller search coils. White's TM 808 can detect 55 gallon drums at 16 feet, car-sized metals at 20 feet. However, it is not likely to respond to individual coins or pieces of jewelry.

Detection depth varies with many factors:

The size, shape, exact metal alloy, and orientation of the object in the ground. Objects of a greater surface are detected at greater depths. For example a coin lying flat exposes a greater surface area than a coin laying on its side and will be detected at a greater depth.
The size of the search coil. Search coils come in a wide range of sizes and shapes- 4", 6", 8", 9.5", and 15". There are also differences in the configuration of the coils inside the search coil producing different shape search patterns. The larger the search coil, the deeper it can detect larger metal items. However, it is more difficult to use in trashy areas with less depth to small metal items. Smaller search coils provide better separation in high trash and better sensitivity to small metals.
Soil conditions and the amount of minerals in the soil. The higher the soil mineralization, i.e. the presence of magnetic and/or conductive properties, the more difficult it is for a metal detector to cancel the interference these soils produce. Detection depth is reduced in severe grounds. Depth may increase or decrease with subtle changes in the soil conditions, more noticeably with the entry level models. Soil mineralization varies widely around the country & around the world.
The experience and skill of the operator. There's no substitute for experience. Knowing how to operate your detector and understanding the signals will significantly increase depth.
The metal detector used and the selection of settings, particularly All Metal or Discrimination.

3. What types of things will a metal detector help me find?

All metallic objects. Example: gold, silver, iron, nickel, copper, brass, aluminum, tin, lead, bronze. Metal detectors will not detect nonmetal items such as gemstones, diamonds, pearls, bone, paper, or stone figures.

4. What is discrimination?

Discrimination is the ability of a metal detector to tell the difference between different types or alloys of metals. This allows you to selectively dig up only those types of metals likely to be of interest to them. There are audio (speaker/headphone) types of discriminators and visual (meter, LCD) types. Most higher end models have both types. The idea is to increase the odds in favor of digging valuables, and decrease the odds of digging trash.

5. Can a detector be set only to respond to gold?

No. There are too many variables with exact alloys and sizes to pin it down tightly enough to dig only one type of metal. For example, a large piece of gold may read high on a display or audio discrimination scale and a small piece of gold may read low on that same scale. Gold with some copper, silver, or platinum within its natural alloy will indicate differently. And other metals with similar electrical characteristics may read identically. Lead and aluminum are the most difficult common trash metals to eliminate. Even with the most sophisticated detectors available, expect to dig some trash. But a good discriminator increases the odds in your favor.

6. What is operating frequency?

Frequency in a metal detector is referred to in kHz. (kilo hertz). It is the number of times the signal is transmitted and received by the detector every second. For example a metal detector operating at 6 kHz will transmit and received 6,000 times per second, and at 50 kHz 50,000 times per second.

As a rule, lower frequency detectors offer better sensitivity to copper and silver and better overall detection depth and trash rejection. Most general purpose models operate at lower frequencies.

Higher frequency detectors are more sensitive to small metals and natural gold. However, they have difficulties with discrimination against nonferrous (not-of-iron) metals. Their sensitivity to small metals makes them tedious to use around trashy areas. Most gold prospecting detectors operate at higher frequencies.

7. Are there any good places left to hunt?

Nobody gets it all. Just because an area has been hunted before doesn't mean a person with patience and a modern detector can't still find the "good stuff" just about anywhere. Spending time with research can still turn up places which may never have been searched. Seasonal changes such as storms, frost heaves, and erosion, can also renew areas, particularly beaches.

8. What is the difference between "two filter" Classics and the higher end "four filter" models?

Two filter and four filter are terms used to describe the amount of electronic circuitry a metal detector uses to deal with both discrimination and ground mineral elimination. A two filter model will work great in low to medium ground minerals and offer faster response between close together targets in trashy areas. Two filter models are user friendly, lightweight, and less expensive. Four filter models typically detect deeper in mineralized ground, have superior audio discrimination and depth, and offer more advanced features.

9. What will target ID displays or meters do for me?

Many models have displays that indicate the likely identification of the metal detected. This is in addition to the audio discriminator. Once an audio signal of interest is heard the display will give a second, independent, opinion about whether the target is a good target, or trash. You dig less trash with an ID display.

ID displays are a very accurate measure of a targets "electrical phase". Unfortunately, many different metals have the same electrical phase. The Target ID will increase your odds of digging good alloys and decrease your odds of digging trash alloys. If, in a given area, a particular indication consistently turns out to be trash, such indications in that area are likely to continue to be trash and can be ignored.

10. I want to go metal detecting with friends and family. Will more than one detector interfere with each other?

Yes. Like models operating on the same frequency will interfere with each other if operated within 100 feet. To search with a partner nearby, at least one of the instruments requires the frequency shifting feature.

11. What about all these different sized search coils? Do I need accessory search coils?

The standard equipment search coil is ideal for all-around searching. A person may want to use a smaller search coil for extreme trash (lots of close-together targets). A person may want to use a larger size for increased depth. Larger search coils 15", are recommended for larger targets (jars of coins) at extreme depths. Remember, with a 15" search coil, sensitivity to coin sized targets decreases.

12. What about a carrying case for my metal detector?

For everyday use, the gun style detector bags are recommended. The detector and accessories can be installed and removed easily, without taking the detector apart. Shock-proof cases are intended for more serious storage and travel.

13. Do I need headphones?

Headphones will increase battery life, increase privacy, and increase your ability to hear signals clearly against background noise. They are of benefit to those even with good hearing. Crisp sound is typically more important than wide frequency specifications. In most cases, higher impedance headphones (100 ohms) offer crisper sounds.

14. What about rechargeable batteries?

Rechargeable batteries will save you money if you use your metal detector often, at least once or twice a week. If you use your metal detector once a month, rechargeable batteries will not likely save you money. Rechargeable batteries do offer the same metal detection performance - most models use a voltage-regulated system.

15. Where can I use a metal detector?

You must have permission to search both private and public property from the owner or person in charge of managing the property. In most cases you can locate the owner, or available permit system, through City Hall or the county seat.

If the area is city owned contact the Parks and Recreation Department. If it is a State or Federal Park contact the superintendent or grounds keeper. Known and marked historical sites, historical parks, and historical monuments are typically off limits to all metal detecting.

Start with your own yard. Valuables can be found anywhere people have congregated, gathered, lived, sat, walked, played, camped, picnicked, traveled, or fought. Any place inhabited before 1965, is likely to have the older styles of collectible coins.

16. How do I recover the target once I decide to dig it up?

Care must be taken to use the appropriate digging tool for the terrain, and not to leave unsightly excavations or holes. There are hundreds of digging tools designed to minimize the impact on grass and vegetation, and avoiding damaging the items found. Sand scoops are all that is needed in some areas. In others, a hand gardening trowel or spade. Challenging ground conditions may require more sophisticated tools.

Some areas may have rules on the type and size of digging tools allowed. Make yourself aware of these rules; respect the laws and restrictions in your area. Unsightly holes left unfilled are dangerous to people and livestock, and are detrimental to the continued use of detectors.

17. What is sweep speed?

All modern detectors require some movement (sweep) of the search coil in order to respond to metals. If the search coil is swept too slowly, metals do not respond, or do not respond at as great of depths. Every model has an ideal search coil sweep speed, usually between two and four seconds per pass. Experimenting to find the ideal search coil sweep speed allows optimum detector performance. A first time user typically has to practice to find their comfortable search coil sweep technique. Seeing others with good search coil sweep habits is a big aid in learning. Practice makes perfect. The desire is to sweep the search coil evenly with the ground in smooth even swings. Overlap each pass by at least 50%, always keeping the search coil in motion. Recognizing where the beep is on each pass and shortening the passes to zero in on the location (pinpoint) takes some practice as well.

18. What about the after-market devices that are said to add depth to my detector, do they work?

A well-designed metal detector has all the usable detection depth (gain) built into standard features. The only way to significantly increase depth is to maximize the standard features or use a larger search coil. There are many aftermarket devices that can make it easier to hear the metal detector, giving the impression of greater depth. Their degree of success depends on the individuals hearing abilities.

19. I want to go nugget shooting once a year, beach combing once a year, and the rest of the time I want to coin and relic hunt. What model of instrument should I be looking at?

A general purpose would give you the best all-around performance. Only when beach or prospecting consumes the majority of your search time would it be wise to look at a model specifically for that purpose. Although prospecting or beach models offer increased performance for their purpose, they are not as effective as a general purpose models for coin and relic hunting.

No comments:

Post a Comment