Minelab GP 3500 User's Manual

1. Introduction

Introducing the Minelab GP 3500

The Minelab GP 3500 utilizes “Dual Voltage Technology” (DVT) for accurate ground balance and increased sensitivity, particularly in heavily mineralized ground. Key features include:

• NEW Quick-Trak push button for fast, accurate ground balancing.
• NEW Manual Tune control for precise interference control and frequency band selection.
• Operator select 3-Speed Ground Tracking.
• Improved “Smart Point” diagnostic plug.
• Separation of Level Adjust functions.
• Easy Adjust Bow Knuckle and hand strap.

The GP 3500 is designed to handle heavily mineralized and salty ground conditions with greater ease than previous models, opening up new detecting areas. Its new Low-Noise circuitry provides a smoother threshold, enhancing the ability to hear faint signals from small and deep targets.

Unpacking your GP 3500 [easy reference]

The GP 3500 package includes the following main components:

• Shaft Assembly (A): Includes Upper Shaft (8) and Handle with Quick-Trak push button (9).
• 11 inch Coil (B): The standard Double D coil (1) with Skid Plate (3).
• Headphones (C): Standard headphones (16).
• Control Box (D): The main unit housing the electronics.
• Battery and Backpack (E): Includes Battery (17), Battery Back-Pack (18), and Battery Power Cable (19).
• 12V Charger (F): For charging the battery.
• Mains Charger (H): For charging the battery.
• Power Lead (I): Connects the battery to the charger.
• Arm Rest (J): Part of the shaft assembly.
• Instruction Manual (K): This guide.

Figure 1.1 shows the contents of the GP 3500 pack, illustrating the main components.

2. Assembly

List of pre-assembled sections and parts

The GP 3500 is shipped with several sections pre-assembled. The main components are:

• Shaft Assembly: Includes Upper Shaft (8), Handle with Quick-Trak (9), Armrest Parts (11), Nylon Bolts (12), Nylon Nuts (13), Arm Straps (14), Armrest Cover (15).
• Coil Assembly: 11 inch Double D Coil (1) with Skid Plate (3) and Coil Cable (2).
• Control Box: The main detector unit (10).
• Battery and Pack: Battery (17), Battery Back-Pack (18), Battery Power Cable (19).
• Headphones: (16)
• Extras: Velcro Cable Straps (20), Bungy Cord (21), Bungy Knuckle (22).

Figure 2.1 illustrates these pre-assembled sections and parts.

Complete assembly instructions

Attaching the coil

1. Ensure the coil (1) has a skid plate (3) attached.
2. Insert two teardrop washers (5) into the indentations on the end of the lower fibreglass shaft (4). These washers should be full thickness and replaced regularly to prevent the coil becoming loose.
3. Push the lower fibreglass shaft (4) into the coil's mounting brackets, ensuring the spring clip faces the rear of the coil.
4. Align the holes in the coil with the pivot end of the fibreglass shaft (4). Insert the nylon bolt through the holes and secure with the nylon wing nut, tightening by hand. Avoid overtightening to prevent crushing the coil housing.

Figure 2.2 shows the coil pivot end of the lower fibreglass shaft with washers and fasteners.

Assembling the lower and upper shaft sections

1. Slide the lower shaft (4) with the attached coil into the end of the upper shaft (8). Snap the spring clip into place.

Attaching the handle and arm rest

1. Slide the bow knuckle (22) onto the upper shaft (8) and position it halfway down.
2. Slide the handle (9) onto the upper shaft (8) and slide it down.
3. Place the two armrest halves (11) on either side of the upper shaft (8), aligning the bolt holes.
4. Insert two nylon bolts (12) through the aligned holes and screw on the nylon wing nuts (13) by a couple of turns.
5. Attach the armrest straps (14) using the press studs on the armrest.
6. Thread the armrest straps (14) through the slots in the neoprene armrest cover (15) and slide the cover over the armrest (11).
7. Position your arm in the armrest and adjust the handle for comfort. Tighten the two screws at the base of the handle with a small screwdriver.

Tip: For optimal balance, the rear of the armrest should be just in front of your elbow.

Figure 2.3 illustrates the armrest attachment process.

Attaching the Control Box and achieving balance

1. Position the T-section of the control box (10) onto the armrest, with the battery plug at the rear. Hand-tighten the nylon wing nuts.
2. Route the Quick-Trak button cable from the handle along the shaft and plug it into the Smart Point connection in the control box (10).
3. Adjust the shaft length and coil angle for a comfortable position. The lower fibreglass shaft is secured by a spring clip into holes on the upper shaft, and a locking nut. The correct shaft length allows the coil to be swung forward without bending or straining your shoulder.

Figure 2.4 shows the handle and bungy cord connection.

Securing and connecting the coil cable

Note: Always turn the control box OFF before connecting or disconnecting the coil to prevent damage to the electronics.

1. Wind the coil cable around the shaft and plug the coil connector into the control box socket. Ensure the cable is wound firmly without strain, leaving enough slack near the coil for angle adjustment without stressing the cable.
2. Secure the cable using the provided Velcro straps (20).
3. Thread the bungy cord through the bow knuckle (22). Slide the knuckle up or down the shaft (8) to find the balance point and tighten the wing-nut.

HINT: Loose coil cables can be 'seen' by the detector, causing confusing random noises.

Fitting and connecting the battery pack

1. Fit the battery (17) into the backpack pouch (18).
2. Connect the headphones (16) and the power cable (19) to the appropriate sockets on the battery cap.
3. Put on the backpack (18).

CAUTION: Use only the 6V battery supplied.

Figure 2.5 illustrates the GP 3500 battery assembly.

4. Ensure the power switch on the control box is OFF before plugging the power cable connector (19) into the control box socket. This cable connects the battery and headphones to the detector.

Adjust for your own comfort

1. Adjust the bungy cord (21) from the knuckle (22) on the shaft to take some of the weight during prospecting.
2. Adjust the hand strap on the handle (9) for comfort.
3. Adjust the battery bag's rear harness strap so the battery sits comfortably on your back. The ideal position balances the detector's weight and allows easy operation of the detector's controls.

TIP: Adjust the bungy cord length or bow knuckle position when changing coils or detecting on slopes.

3. Batteries

The Battery

The 6V rechargeable battery provides approximately 14-15 hours of operation when fully charged. The battery can be recharged at any time. It is crucial to fully charge the battery before storage and not leave it discharged for more than one day.

CAUTION: Never use a 12V battery, as this can damage the detector and void the warranty. The GP 3500 has internal voltage regulation; external regulated power supplies are not necessary and may cause damage. For extended operation, consider owning a spare battery.

Low battery indication: A series of alarm pulses at half-second intervals signals when the battery power is insufficient.

Charging the battery

1. Turn the detector OFF before disconnecting the battery.
2. Disconnect the battery cable from the detector and connect it to the appropriate charger.

Battery chargers: Mains and 12V Vehicle Chargers are supplied.

Important: Keep the battery upright during charging.

Mains battery charger

The mains charger charges the battery from AC power outlets. Connect the charger to a mains outlet, then to the battery using the power cable, and finally switch on the mains outlet. A fully discharged battery takes approximately 24 hours to charge. Partially discharged batteries will recharge faster. Allow 1.5 to 2 hours charging for each hour of use. The charger's LED flashing rate decreases as the battery charges.

Vehicle battery charger

The vehicle charger uses a vehicle's cigarette lighter socket. Connect the charger to the socket and turn the ignition switch to 'Accessories'. Connect the detector battery to the charger via the power cable. The charger converts the vehicle's 12V supply to charge the detector battery. A red LED flashes during charging; a fast flash may appear constant when the battery is flat, slowing as it charges. Allow approximately 10 hours for charging. The charger stops if the vehicle battery voltage drops below 11V. Ensure your vehicle battery is in good condition and run the engine periodically to maintain its charge.

CAUTION: The vehicle charger is designed for negative earth electrical systems. Connecting to a positive earth system may blow the fuse in the cigarette lighter plug. Use a 3ag/10amp fuse for replacement.

4. Controls and Operation

Detector sounds [easy reference]

The detector produces various sounds. Understanding them is key to operation:

• Threshold and Tone: The background hum set by the Threshold and Tone controls.
• Target Signal: An abrupt change in tone and volume when a target is detected. Maximum level is set by Volume; tone variation by Signal. A falling-then-rising tone often indicates a large target, while a rising-then-falling tone suggests a small target.
• Ground Noise: Irregular noises from ground mineralization. Proper ground balance minimizes this.
• Tune Indication: An initial beep, followed by a period of threshold adjustment, concluding with three sharp beeps when optimal frequency is found.
• Low Battery Indication: Alarm pulses at half-second intervals indicate low battery power.

Quick start instructions [easy reference]

1. Set Coil switch to Double D.
2. Set Soil switch to N (Normal).
3. Set Balance switch to Fixed.
4. Set Iron Discriminate knob to All Metals.
5. Set Boost to N (Normal).
6. Set Volume to maximum and Signal to 2 o'clock.
7. Turn Power Switch ON and adjust Threshold for a faint audible sound.
8. Adjust Tone for comfortable hearing.
9. To tune out interference, hold the detector horizontally at waist height with the coil vertical. Slowly sweep the coil around your body until interference is loudest.
10. Place the detector on the ground in that position and press the Tune button once. Leave the detector undisturbed during the approximately 60-second tuning process. Three beeps confirm completion.
11. Keep the All Metal / Disc control in the All Metal position.
12. Set Balance to Fixed. While moving the coil up and down, press and hold the Quick-Trak push button to engage Tracking Mode.
13. Release the push button once Ground Balance is achieved.
14. The detector is now ready for operation.

Rear Control Functions – Rear Panel

The GP 3500 features two control panels. The rear panel includes:

• Threshold: Controls the background hum. Set for a stable, just audible level.
• Volume: Adjusts the loudness of target signals. Set for clear, comfortable listening.
• Tone: Adjusts the pitch of the threshold to suit your hearing.
• Signal: Controls the variance of the target signal's pitch and volume change. Higher variance can offer more signal definition but may cause confusion in noisy ground.
• Boost: Selects processing and filtering for different target signals (Shallow, Normal, Deep).
• Soil: Optimizes detector for soil conditions (Sensitive, Normal, Salt).

Figure 4.1 shows the rear control panel layout.

Front Control Functions – Front Panel

The front panel controls include:

• Tune: Reduces electromagnetic interference. Features an Auto push button for automatic tuning and a manual control for fine-tuning.
• All Metal/Iron Discriminate: Distinguishes between ferrous and non-ferrous metals. In 'All Metal' mode, all metals are detected. In 'Disc' mode, ferrous (iron) objects cause the signal to be momentarily blanked.
• Coil Switch: Selects the search pattern and sensitivity for different coil types (Double-D, M (Mono), Cancel).
• Balance Switch: Selects between Fixed ground balance and automatic Tracking ground balance.
• Smart Point: A diagnostic/test port and connection for the Quick-Trak button.

Figure 4.16 shows the front control panel layout. Figure 4.17 highlights the Smart Point connector.

Threshold - On/Off

The Threshold control turns the detector ON/OFF and sets the background hum (Threshold). It should be set at a stable, just audible level. Small target signals may only cause slight variations in the threshold, which can be missed if the threshold is set too high or too low.

Figures 4.3, 4.4, and 4.5 illustrate threshold levels: too high, too low, and just right, showing how signals are perceived relative to the threshold.

Volume

The Volume control sets the maximum loudness of target signals. Setting it to maximum allows the signal to be proportional to target size and depth. Reducing the volume limits the signal for larger targets. Turning it near minimum may cause targets to be lost.

Note: Reset Threshold after adjusting Volume. Set Volume for clear, comfortable target signals.

Figures 4.7, 4.8, and 4.9 illustrate volume levels: maximum, mid-range, and minimum, showing how signal loudness is affected.

Tone

The Tone control adjusts the pitch of the threshold. Setting it to a preferred pitch can enhance hearing sensitivity. Adjust until the threshold is comfortable and provides the best signal response. A higher pitch may be fatiguing but aids in identifying soft target signals.

Figure 4.10 shows the Tone control.

Signal Audio

The Signal control determines the variance of the target signal's tone and volume change. Higher variance can provide more signal definition but may cause confusion in noisy ground. It adjusts the pitch response, allowing for deeper pitches for small targets that rise to a higher pitch.

Figures 4.12 and 4.13 illustrate reduced and increased pitch variance, respectively.

Boost (Shallow/N/Deep)

The Boost switch selects processing and filtering to enhance target signals. 'N' (Normal) is for general detecting. 'Shallow' boosts signals from small, near-surface targets. 'Deep' is for large targets at greater depths in noisy ground, smoothing random soil signals.

Note: Adjusting Boost may require re-adjusting Threshold. External amplifiers can be used if they have loudness limiters.

Figure 4.14 shows the Boost switch.

Soil (Sensitive/Normal/Salt)

This switch optimizes the detector for different soil conditions. 'N' (Normal) is versatile for most areas, including highly mineralized soil. 'Sensitive' is for small nuggets in highly mineralized ground, allowing the coil to be closer to the ground but may reduce depth for large nuggets. 'Salt' is for areas with high salt content.

Figure 4.15 shows the Soil switch.

All Metal/Iron Discriminate

Discrimination allows the detector to differentiate between metal types. In 'All Metal' mode (anti-clockwise), all metals are detected. Rotating clockwise engages ferrous discrimination, where iron objects cause the signal to be 'blanked' or silenced. This is useful in areas with high trash content.

Note: If target response is too weak for discrimination, a normal signal is given. Adjusting the control further clockwise increases the likelihood of detecting ferrous targets.

Discrimination - continued: Iron discrimination blanks the threshold and target signal for ferrous metal. 'All Metal' mode has no discrimination. When using 'Disc' mode, sweep the coil rapidly over the target center, with Ground Balance set to Fixed. Test from at least two directions. A ferrous target signal starts normally but blanks when strong enough.

TIP: For very deep targets, discrimination accuracy may be reduced if the hole is too small for sideways coil movement.

The strength of the target response required for discrimination can be adjusted by rotating the knob. Rotating anti-clockwise requires a stronger signal for discrimination, while clockwise allows discrimination on weaker targets. Discrimination functions best with strong, positive target responses.

HINT: Dig out all targets unless impractical due to excessive rubbish. Discrimination works best with GP Series Double-D coils.

Note: For pinpointing, switch to 'All Metals' mode.

TIP: On known gold sites, dig all targets.

Figures 4.18, 4.19, 4.20, and 4.21 illustrate the All Metal/Iron Discriminate switch and discrimination levels.

Coil (Double-D/M/Cancel)

This switch changes the coil's sensitivity and search pattern for different environments. 'Double-D' is for conventional Double D search patterns, offering stability in mineralized ground and good for pinpointing. 'M' (Mono) increases sensitivity but can be less stable in mineralized ground; pinpointing is off-center. 'Cancel' provides stability in areas of electrical interference, ideal near suburbia or power lines, but limits sensitivity to deep targets.

Note: Use coils specifically designed for the GP 3500 for optimal performance. Minelab Monoloop coils work well in 'M' mode. In extreme mineralization, keep the coil slightly off the ground or use 'Double D' mode to avoid signal spikes.

IMPORTANT: Re-ground balance whenever changing the 'Coil' switch position.

Figure 4.22 shows the Coil switch.

Balance (Fixed/Tracking)

Ground mineralization can cause 'ground noise'. The GP 3500 automatically cancels this effect via ground balancing. 'Fixed' mode maintains the current ground balance, with Quick-Trak used for re-balancing. 'Tracking' mode continuously adjusts to changing mineralization. For variable ground, Tracking is preferred.

Ground Balancing Procedure: Set Balance to Fixed. Move the coil 20-100mm above the ground and press the Quick-Trak button. Keep moving the coil and the button pressed until ground noise stops. Release the button when the threshold is stable. You are now in Fixed position.

Tip: If ground noise persists, try a new location.

Figure 4.23 shows the Balance switch. Figure 4.24 illustrates the Ground Balancing Procedure.

Operating the GP 3500 in Fixed mode

Fixed mode offers better depth in medium to quiet ground. Use Quick-Trak to re-balance when ground changes occur. If ground is highly mineralized or variable, use Tracking mode.

HINTS: Use Fixed for depth; use Tracking for noisy/changing ground. Re-balance periodically in Fixed mode. Pinpoint targets in Fixed mode. Lift the coil slightly if mineralization is excessive.

Operating the GP 3500 in Tracking mode

Tracking mode is for highly mineralized or variable ground. The detector continuously tests and re-balances. There are three tracking speeds: Fast, Medium, and Slow (detailed in the next chapter). In Tracking mode, pressing the Quick-Trak button temporarily switches to Fixed mode for better pinpointing. A weak target response might be missed in Tracking, especially at faster speeds.

TIP: Use the Quick-Trak button as a ground balance reset in Tracking mode.

Tracking Speed

If using Tracking mode, choose the speed (Slow, Medium, Fast) best suited to the area. Fixed Balance is recommended for variable ground. The initial 5-second auto-ground balance is unaffected by the Tracking Speed switch.

Note: Select the slowest speed that keeps up with ground variability.

Figure 4.25 shows the Tracking Speed switch.

Quick-Trak push button

Located in the handle, this button operates ground balancing based on the Balance switch setting. In Fixed mode, it initiates a 5-second fast re-balance when pressed. In Tracking mode, it temporarily switches to Fixed mode for pinpointing. Releasing the button returns to the selected Balance mode after a short auto-ground balance.

Note: The Quick-Trak button only changes operating mode while depressed.

Figure 4.26 shows the Quick-Trak push button.

Tune

The Tune function reduces electromagnetic interference. The Auto push button starts a 60-second automatic tuning process, indicated by three beeps. Interference can change, so re-tuning may be necessary.

Set the Tune control: Tune initially with the Coil switch in Double D or M (Mono). If interference persists, switch to Cancel and re-tune. Hold the detector at waist height, coil vertical, and rotate slowly to find the point of loudest interference. Press the Tune button to start the automatic scan. Keep the coil motionless and clear of metal objects during tuning. Operators should take turns tuning if near other detectors.

Figure 4.27 shows the Tune control. Figure 4.28 illustrates the Tuning Process.

Manual Control

Manual tuning fine-tunes the selected band after Auto-tune. Turn the manual control slowly in one direction, listening for threshold stability. If interference persists, try the Coil switch set to Cancel and re-tune. In benign areas, experiment with frequency bands (counter-clockwise for lower, clockwise for higher) to find a stable setting. Low frequencies may offer more depth for large targets; high frequencies offer more sensitivity for small targets.

Important: The manual control signals the end of the frequency band range with beeps.

Note: Rapid control movement causes temporary noise; slow movement is stable.

5. Detecting

Detecting techniques

Hints and techniques for better detecting:

• Ensure the battery is fully charged for optimal performance. Consider a spare battery.
• Wear the battery in the backpack harness for optimal weight distribution.
• Set the shaft length appropriately to avoid detecting items you are carrying (e.g., pick, battery, boots).
• Experiment with different settings to understand detector capabilities in various locations.

Motion detection

The GP 3500 is a motion detector; the coil must be moving over a target to detect it.

Parallel Sweeping Procedure

• Sweep the coil side-to-side, keeping it parallel and at a consistent height above the ground. Lightly skidding the coil can help maintain height.
• Avoid raising the coil at the ends of sweeps, as this reduces detection depth and can cause false signals.

Figure 5.1 shows correct and incorrect parallel sweeping techniques.

Prospecting techniques

The GP 3500's superior ground balancing allows finding large objects in areas previously worked by other detectors. Dig all target signals, even in previously detected areas.

• Sudden mineralization changes can cause broad signals, often in one direction.
• Responses from reddish dyke material or clay may occur; metal targets become louder as the coil gets closer.
• In variable mineralization, sweep with contours rather than across changes.
• In heavily mineralized ground, sweep the coil 1-2 cm above the ground for a more stable threshold.
• For faint signals, scrape a few centimeters of surface soil to check if the signal clarifies.

Big GOLD

Larger gold pieces often give a broad signal with little pitch variance, differing from smaller targets. This can lead to disappointment if not understood.

For Maximum Gold Recovery

• Keep the coil as close to the ground as possible.
• Listen very carefully; this is more important than looking.
• Slow down your sweeping speed.
• Maintain a positive mindset.
• Thoroughly search small areas rather than randomly covering large ones.

Identifying target signals

Metallic targets typically produce a 'solid', short, sharp, symmetrical signal. Ground noises are usually broad, uneven, and may only signal from one direction.

Investigation: If unsure, scrape a shallow hole (70-100mm) over the suspected target. Sweep the coil over the hole at ground level. If the signal decreases or becomes less defined, it's likely ground noise. If it remains the same or louder, it's a metallic target. If still unsure, deepen the hole and repeat.

A 'halo effect' can make buried objects appear larger. This effect reduces once the object is disturbed. Do not try to eliminate faint ground noise by balancing over it, as this may cancel out a deep target response. Instead, ground balance around the target, switch to Fixed, and try Pinpointing.

Figures 4.20 and 4.21 illustrate signal responses.

Pinpointing

To pinpoint a target, first confirm it with accurate ground balance. In Fixed mode, hold the Quick-Trak button while sweeping the coil around the target area (avoiding the target itself) until it's not detected, then release the button. In Tracking mode, move the coil away from the target, hold Quick-Trak to switch to Fixed, then pinpoint across the target. Sweep the general area, noting where the strongest signal is received. Shorten the sweep to define an imaginary line. Repeat at 90 degrees to find the exact location where the lines cross.

Note: Pinpointing may be slightly off-center with Coil switch in M (Mono) or Cancel modes.

Figure 5.4 illustrates the pinpointing technique.

Recovering the target

Once a target's location is confirmed, dig carefully to preserve the environment, making the hole as small as possible. Always replace soil and grass afterward.

Essential digging tools: Small spade/shovel, pick with broad scraping blade, crowbar for hard ground.

1. Before digging, clear surface material and check the target signal. Note any other nearby signals to avoid burying them under diggings.
2. If the signal is present, dig to approximately 50mm depth. Sweep the coil over the hole. If the signal is gone, it's in the diggings.
3. If the signal is still present, dig deeper.
4. Take care not to damage the target when digging; start digging approximately 100mm in front of the target.
5. Pile diggings carefully, ensuring no other targets are buried.
6. Sweep the pile to locate the target if it's in the removed soil.
7. Halve the pile containing the target to narrow down its location.
8. If still difficult to find, place the detector horizontally and pass handfuls of diggings over the coil.

Note: Remove all metallic jewelry and watches before handling diggings.

Important: Always refill holes and scatter leaves to restore the area. Dispose of any recovered rubbish properly. This helps maintain a good reputation for metal detector users and ensures access to more prospecting areas.

Recovering Deep Targets

The GP 3500 is capable of finding deeply buried targets. Use the cross sweeping method to locate accurately. Dig a hole approximately 100mm deep. Keep testing the location as you dig deeper. Be careful not to dig past the target. Try pinpointing again to confirm the hole's position.

HINT: After recovery, sweep the hole again to ensure no other targets remain.

If an object is found, search the surrounding area carefully, as more objects may be nearby.

Salty Environments

The GP 3500 performs well in salty environments, but strong salt interference may require specific settings. Change the Soil switch to 'Salt' and use specially designed GP series coils.

6. User Information

Technical specifications for the Minelab GP 3500

Note: Minelab reserves the right to make changes without notice for product improvement.

Troubleshooting

If returning the detector for service, provide detailed fault information. Return the detector in a protective box with a copy of the Service Repair Form, your contact details, purchase date, and serial number.

Do not open the control box, as this will void your warranty.

Service repair form

The service repair form requires details such as:

• Today's date
• Detector Model
• Purchased from
• Purchase date
• Faulty part(s)
• Description of fault
• Owner's name, address, phone, fax, email

Warranty

The GP 3500 control box has a 2-year warranty for parts and labor. GP series coils have a 1-year warranty against malfunction. Refer to your supplier or Minelab for service. The warranty commences from the date of purchase and does not cover damage from accident, misuse, neglect, modifications, or unauthorized service. The warranty is not transferable unless the registration card is returned within 14 days of purchase.

Owners are responsible for all transport costs to Minelab; repaired detectors are returned freight-free.

Repairs

For service, fill out the Minelab Service Repair Form and enclose it with the detector. Provide as much detail about the fault as possible to assist service engineers.

Glossary of common terms

• Control Box: Encloses circuitry, originates TX signals, interprets RX signals. Features user-selectable controls.
• Discrimination: Ability to distinguish ferrous from non-ferrous metals.
• Double-D Coils: Coils with overlapping windings, offering stability, depth, and sensitivity.
• Electromagnetic Field: The pulsed field generated by the coil that interacts with metal targets.
• False Signal: Sounds similar to target signals but caused by factors like incorrect ground balance, hot rocks, or coil impacts.
• Ferrous Metals: Metals containing iron, attracted to magnets.
• Ground Balance: Compensates for ground mineralization to minimize noise and maximize sensitivity. The GP 3500 has automatic ground balance.
• Halo Effect: Diffusion around a long-undisturbed metal object, making it appear larger to the detector.
• Hot Rocks: Rocks with high mineralization causing false signals.
• Interference: Electrical or radio waves causing detector instability (e.g., from power lines, other detectors).
• Mineralization Ground: Ground containing minerals that can cause false signals. Heavily mineralized or salty ground requires specific processing.
• Monoloop Coils: Coils with a single loop winding, often cone-shaped.
• Non-Ferrous Metals: Metals without significant iron content (e.g., gold, silver, copper).
• Pinpoint: Method to locate a target's precise position before digging.
• RX: The received electromagnetic field used by the control box to detect metal items.
• Salt: High salt content in ground affects ground balance similarly to mineralization, often causing a negative response.
• Search Coil: The circular plate swept over the ground, transmitting and receiving signals.
• Search Pattern: The area covered by each coil sweep, varying by coil type and mode.
• Threshold: The continuous audible background sound of the detector, adjustable for level and tone.
• Target Response: The electromagnetic effect from a metal target under the TX field.
• Target Signal: The audio signal indicating a detected metal target.
• Tracking: Automatic ground balance that continuously compensates for mineralization changes.
• TX: Transmit signals or electromagnetic pulses sent into the ground by the coil.

Detector care and safety

The GP 3500 is a high-quality instrument designed for professional use. Keep it clean and dry, especially electrical connectors. The control box is water-resistant but not waterproof; avoid immersion. The coil is water-resistant but not waterproof. Regularly replace wear items like washers and skid plates. Avoid high temperatures and direct sunlight. Clean with a damp cloth and mild soap; do not use solvents. Do not open the control box, as this voids the warranty. All repairs should be sent to Minelab or an authorized repairer.

Accessories

The GP 3500 is supplied with an 11" Double D coil. Other coil sizes are available for improved performance, offering greater sensitivity to small targets or greater depth. Other brands of Double D and Monoloop coils may work but may limit DVT technology benefits or cause instability. Spare 12Ahr batteries are recommended for extended use. A smaller, lighter 4.5Ahr battery is also available, providing 3-4 hours of running time.

Minelab also offers corporate clothing such as caps, shirts, and jackets. Inquire with your local dealer.

Environmental Compliance: The GP 3500 is designed for hobbyist use and not as a mine detector. For European consumers, dispose of the equipment responsibly via recycling services, not general household waste.