I never did find this out. Why can the Minelab Eureka Gold change to 3 different frequencies with the flip of a switch on the same coil, without changing coils?? When our X-Terra's need to change coils for each frequency. What is the reason that Minelab engineers can't make a X-Terra with one coil for 3 frequencies? Thank you if anyone knows the answer.
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3 frequencies with one coil?
- Thread starter David
- Start date
nero_design
New member
I'm guessing here but the Concentric Coil shape (the default stock coil) is easily configured into any frequency. But the cone shaped EMF from this coil requires more overlapping to cover the soil PLUS it's not as suitable to working on mineralized ground (typical of the Goldfields) as a Double-D coil is. On a beach or in a park, the Concentric coils are a little deeper seeking but they fail to penetrate the mineralized soils as well as a Double-D coil can The Double-D coils offer more ground coverage and better depth on Mineralized ground plus they are more stable on mineralized ground and offer more reliable Target ID.
Remember that the Eureka is a robust "analogue" detector that was made before the "digital" X-Terras became a hit. It has little in the way of Ground Tracking, Ground balancing and Noise cancel. An advantage of a dedicated-frequency coil is "strength of signal". Most people hunt with one frequency or thereabouts when using a VLF detector and Gold nuggets tend to peak around 20khz when searching for an "average" sized nugget at depth - so the X-Terra HF coils are in the 18.75khz range. But smaller targets will respond with higher frequencies (eg specimen gold in quartz) and this is what the Eureka Gold does. That's also why it is targeted at the Gold Hunter.
The Eureka Gold is a Gold-specific detector whereas the X-Terras are "multi purpose" and allow users to hunt for Coins, Jewellery & Relics as well as Gold Nuggets. Both detectors fill their own niche. As a nugget hunting unit, the Eureka has a frequency selector switch whereas the X-Terras offer a range of different frequency coils. Not many coin-hunters are going to use Prospecting Mode. And fewer will need multiple coils. But a Eureka Gold currently offers three useful frequencies in one detector. There's a Chip in the X-Terra coils which tells the Control Box which coil is mounted and how to communicate with it so at present the user has to change coils and coil configuration to match the targets being sought..
Remember that the Eureka is a robust "analogue" detector that was made before the "digital" X-Terras became a hit. It has little in the way of Ground Tracking, Ground balancing and Noise cancel. An advantage of a dedicated-frequency coil is "strength of signal". Most people hunt with one frequency or thereabouts when using a VLF detector and Gold nuggets tend to peak around 20khz when searching for an "average" sized nugget at depth - so the X-Terra HF coils are in the 18.75khz range. But smaller targets will respond with higher frequencies (eg specimen gold in quartz) and this is what the Eureka Gold does. That's also why it is targeted at the Gold Hunter.
The Eureka Gold is a Gold-specific detector whereas the X-Terras are "multi purpose" and allow users to hunt for Coins, Jewellery & Relics as well as Gold Nuggets. Both detectors fill their own niche. As a nugget hunting unit, the Eureka has a frequency selector switch whereas the X-Terras offer a range of different frequency coils. Not many coin-hunters are going to use Prospecting Mode. And fewer will need multiple coils. But a Eureka Gold currently offers three useful frequencies in one detector. There's a Chip in the X-Terra coils which tells the Control Box which coil is mounted and how to communicate with it so at present the user has to change coils and coil configuration to match the targets being sought..
BarnacleBill
New member
Optimization is the reason. You cannot optimize a coil for three frequencies as well as for one. It is difficult enough to have consistency from one coil to the next of the same type and frequency during production. Hence the IC chip in the X-Terra coils, one of it's purposes is to optimize that unique individual coil for that frequency. That concept is taken even further in that the Control Head recognizes the different coils when they are attached and does further optimization. Page 48 of the X70 manual shows some of the technology in action vis a vis coil recognition.
some time ago I asked Minelab about changing the operating frequency of a coil, by changing the information on the microchip in an X-Terra coil. Summarizing, here is their response.............
X-Terra coils use tuned circuits for the transmit side, which boost the voltage across the transmit winding. They use the headphone amplifier of the codec as a transmitter. Doing this allows them to get more than 20V peak across the coil, from a supply of 3.3V. The X-Terra coil consists of the transmit winding (with inductance L, resistance R and a capacitor C), resulting in a simple series resonant LCR circuit. The resonant frequency is different from coil to coil due to the winding and capacitor tolerances. In production, when they calibrate the coils, they measure this frequency and record it in the X-Terra coil's micro-controller. When the detector starts, it talks to the micro-controller in the coil and retrieves the value of the resonant frequency (and other parameters). Therefore, it is not possible to change the frequency of the coil by just changing the information in the micro-controller. With Eureka, the tuned circuit is made out of the Tx winding inductance (which is in the coil) and several capacitors (located in the detector). This is why you can change the frequency of Eureka with the switch while using the same coil. The solution chosen for X-Terra is low power and very reliable.
Hope this explains it for you. HH Randy
X-Terra coils use tuned circuits for the transmit side, which boost the voltage across the transmit winding. They use the headphone amplifier of the codec as a transmitter. Doing this allows them to get more than 20V peak across the coil, from a supply of 3.3V. The X-Terra coil consists of the transmit winding (with inductance L, resistance R and a capacitor C), resulting in a simple series resonant LCR circuit. The resonant frequency is different from coil to coil due to the winding and capacitor tolerances. In production, when they calibrate the coils, they measure this frequency and record it in the X-Terra coil's micro-controller. When the detector starts, it talks to the micro-controller in the coil and retrieves the value of the resonant frequency (and other parameters). Therefore, it is not possible to change the frequency of the coil by just changing the information in the micro-controller. With Eureka, the tuned circuit is made out of the Tx winding inductance (which is in the coil) and several capacitors (located in the detector). This is why you can change the frequency of Eureka with the switch while using the same coil. The solution chosen for X-Terra is low power and very reliable.
Hope this explains it for you. HH Randy