DD/concentric temperature tolerances

[marcomo]

I remember reading in the past that a DD/Widescan coil cannot handle being in high temperatures as well as a concentric.

Assuming this is true, can anyone elaborate on why?

 

[Critterhunter]

Check the Etrac or Explorer forum where I responded to this.

 

[Nauti]

The problem with all coils is that when they are tuned at the factory,they are tuned at the temprature in the surrounding area at that time.So if for arguments sake the coil was tuned in an air temp of 25 degrees this will be the optimum temp for that coil to operate at full efficiency.When these coils are used in the field the surrounding temp either expands or contracts the coil windings sending them off their optimum tune.I do not know how much this effects the performance of a coil but i do not think it will make a disastrous difference in most cases.One machine that copes with this phenomonen well is the Nautilus.When you set this machine up in the field you have to balance the coil every time,thus balancing the windings to the ambient temp.This ensures that Nauti coils are operating at peak performance whatever the temp.

 

[Critterhunter]

That's all very true. I'll say (which I did in the other forum) that DD coil design seems less prone to errors in winding alignment than a concentric. They are also less picky at tuning and that's probably why more people build these at home than a concentric, along with being easier to tune using simple test equipment versus what a concentric can need. Slight changes in temperture can cause windings to move and coils to get out of alignment. This is why a coil fill false for a second when you bump it into something. I'd also be weary of white coils. Based on my experience with a 12" concentric aftermarket coil for Whites that was also colored white I think they did that to try to keep the temperture of the coil from getting too high and causing falsing. I tried two brand new ones and they would get unstable after about ten minutes in the field.

Took me a long time to put two and two together as to what was going on. Only after reading up on building my own coils did I figure that one out. Coil would work fine for about ten minutes and then go crazy despite sensitivity adjustment. Turn the detector off and on and it's still going bonkers. Throw it in the car and drive to a new location and now it works fine again. Thinking maybe it was interference at the other spot until once again about ten minutes later it goes nuts. These coils also had a "mushy" feel to them in that they weren't completely filled with epoxy. You could push down on the coil's case and it would flex. I never saw that in a coil before, and the lack of being filled with epoxy probably was what was causing the windings to shift with slight temperture changes.

 

[marcomo]

Interesting stuff that I wasn't aware of. Thanks for sharing, Critterhunter.