larger concentric coils

[hitchhiker]

if there was a larger concentric coil would it get more depth on low mineralised ground?i was just wondering where the cut off point in size of a concentric coil where it goes in reverse as its seeing too much ground in low mineralised ground. So basically my question is whats the biggest concentric coil they could produce to gain maximun depth in mild ground? GL HH

 

[Digger]

My guess is that Minelab has determined that the 9-inch concentric coils we have are optimum for the X-TERRA. Granted, in moderate soil, larger coils will detect larger targets, deeper. But that comes with a "downside" of not being sensitive to smaller targets, such as coins. Although larger coils would cover more ground, another "downside" of having a larger concentric coil could be target separation. The "odds" of target masking by adjacent trash increases as coil size increases. JMHO HH Randy

 

[Old Longhair]

Sounds good to me Randy. I did a little math, and the total volume of soil in the detection field increases dramatically for every inch added really quickly.
As an example, the volume of a 9" hemisphere is 190.62cu.in., a 10" is 261.4cu.in., and a 15" is 874.74cu.in.

 

[hitchhiker]

Thanks for the input, i always wondered if say a 7.5khz 11inch concentric might get that bit deeper than a 7.5khz 10.5in dd coil on coins in very mild ground with little iron as a accessory coil as and when needed. But as you say the 9inch may be optimum depth for coin size targets.
The larger dd coils dont seem to get really that much more depth on coin size targets.But having said that ive only used a bigger dd coil of 7.5khz, which is fractionly deeper than the 10.5inch 7.5 khz dd coil on coins.

 

[mapper65]

My electronics degree tells me that the larger coil you make, the more loading you will have on the transceiver that it is connected to. More loading requires more power to support the larger coil which means shorter battery life. I would expect that this is another major consideration when it comes to coil design.

 

[Digger]

the more loading you will have on the transceiver that it is connected to. More loading requires more power to support the larger coil which means shorter battery life

Interesting you should mention coil size and power consumption. I was messing around with some coil comparisons over the weekend and reached a point where I could plug in a smaller coil and it would start up and work OK. But when I plugged in one of the All Terrain 15-inch coils, it would shut down before it got through the startup process. Went back to a smaller coil and it worked OK. The 15-incher....no go!
I was scratching my head when I noticed the battery indicator was "empty".
I put in a fresh set of AA's and all was well.
I guess Ohm's Law was right.
HH Randy